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Effects of metal corrosion in the pump of a dialysis machine on the sterility of the terminal dialysate by spike-and-recovery testing with bacteria

Effects of metal corrosion in the pump of a dialysis machine on the sterility of the terminal... Background Dialysis units have been concerned that the corroded metal parts of pumps used in hemodialysis might not allow sterility of the pump to be ensured due to bacterial contamination, even after cleaning and disinfec‑ tion are performed after dialysis treatment. The purpose of this study was to clarify the effectiveness of the clean‑ ing/disinfection process in eliminating bacterial contamination of the dialysate in pumps with and without metal corrosion. Methods A suspension of Pseudomonas aeruginosa [10 colony‑forming unit (CFU)/mL] was introduced into pumps without or with corrosion of the metal parts, and the flow in the dialysis circuit was stopped for 6, 12, or 18 h. Then, after cleaning and disinfection of the circuit with a sodium‑hypochlorite ‑ containing reagent, the amounts of live bacteria in the terminal dialysate and on the surface of the metal parts of the pump were counted. Results Irrespective of the presence or absence of metal corrosion, bacteria were detected, even after cleaning and disinfection, on the surfaces of the pump parts that had been left in contact with the bacterial suspension for more than 12 h. However, on the surfaces of the pump parts showing metal corrosion, the bacterial numbers increased dramatically after 18 h of flow stoppage time following introduction of bacteria, and bacteria were even detected in the terminal dialysate despite cleaning/disinfection of the pump. Conclusions Corrosion of the metal parts used in pumps used for dialysis increases the risk of bacterial contamina‑ tion of not only the pump parts and flow path of the dialysis machine but also the terminal dialysate, even if cleaning/ disinfection is performed. For sterility assurance of the dialysis circuit and dialysate during routine use, it is necessary to eliminate corrosion of the metal parts of dialysis pumps during scheduled maintenance. Keywords Bacterial contamination, Sterility, Dialysate, Metal corrosion, Pseudomonas aeruginosa *Correspondence: Minoru Nakamura nakamura‑m@hus.ac.jp Full list of author information is available at the end of the article © The Author(s) 2024. 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The Creative Commons Public Domain Dedication waiver (http://creativecom‑ mons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 2 of 9 irrespective of the presence or absence of corrosion on Background the metal parts of dialysis pumps. Dialysis performed with good-quality dialysate improves The objective of this study was to evaluate the effec - various clinical conditions in dialysis patients [1, 2]. tiveness of cleaning and disinfection on the sterility of Including the international organization for standardiza- a dialysate line and terminal dialysate following expo- tion (ISO) [3], The Japanese Society for Dialysis Therapy sure of the dialysis circuit to a bacterial suspension for and the Japanese Association of Clinical Engineers have various lengths of time of flow stoppage. We propose proposed many updated guidelines for management and an appropriate cleaning and disinfection program using validation of dialysates [4–6]. To ensure the good quality a sodium-hypochlorite-containing reagent approved by of the dialysate, validation and management of the entire the manufacturer for maintaining optimal sterility of dialysate manufacturing process, including the dialysis the dialysate and pumps, on the basis of the results of water treatment system, central dialysis fluid delivery sys - simulation experiments conducted using pumps artifi - tem (CDDS), dialysis machine, and piping to drainage of cially polluted with P. aeruginosa. the dialysate, are necessary. Various cleaning and disin- fection methods have been studied, including the use of sodium hypochlorite, acetic acid, peracetic acid, and hot citric acid solution. High temperatures and high concen- Methods trations of these agents are required for high efficacy in Experimental circuit removing biofilm [7–10]. However, disinfecting CDDS The experimental circuit used to verify the relationship with hot water can be expensive. The manufacturer’s between bacterial contamination of the pump and risk instruction manuals recommend cleaning/disinfect- of contamination of the terminal dialysate simulated a ing with sodium hypochlorite, which is effective against part of the dialysis machine configuration (Fig.  1). An biofilm-forming bacteria [10]. However, prolonged use endotoxin retentive filter (ETRF; Nipro, Osaka, Japan) of sodium hypochlorite can cause metal corrosion. Pre- was installed ahead of the pump to avoid contamina- vious studies have shown that metal corrosion can lead tion from the environment. to increased bacterial contamination [11, 12]. However, The Iwaki Magnet Gear Pump MDG-R2 (Iwaki Co., there is limited research on the effectiveness of disinfec - Tokyo, Japan) was used as the degassing pump in the tion and cleaning for maintaining dialysate sterility when dialysis machine (Fig.  2). The metal parts, the front faced with different flow stoppage times and varying lev - plate and gear case, of the pump were made of stain- els of bacterial contamination in the presence or absence less steel SUS316. Unused new parts were used as parts of metal corrosion in the pump parts. without metal corrosion. Parts used routinely in an Herein, we focused on the relationship between metal ordinary clinical environment for 10  months were cor- corrosion on the metal parts and the risk of bacterial roded, and were used as parts showing metal corrosion contamination in the dialysis machines. According to a (Fig. 3). previous study, numerous bacteria were isolated from corroded metal parts of dialysis machines during clini- cal inspections, although no bacterial contamination was observed in the terminal dialysate samples [11]. We considered metal corrosion to be an important risk factor for bacterial contamination of the dialysate. When pump parts polluted artificially by immersion in water containing Pseudomonas  aeruginosa for 15  h were assembled into a pump in a CDDS line, bacte- rial contamination was found in the terminal dialysate from pumps assembled using corroded metal parts, but not in that from pumps assembled using parts without metal corrosion [12]. Based on these observations, we believe that it would be difficult to ensure adequate ste - rility of the terminal dialysate using the conventional Fig. 1 Experimental circuit. To verify the bacterial contamination cleaning and disinfection program when using dialysis level of the pump and the terminal dialysate, an ETRF was installed pumps assembled using metal parts showing corrosion. ahead of the pump to avoid contamination from the environment. That being said, it is also important to develop opti - Dialysate was introduced into the circuit at a flow rate of 700 mL/min, mal cleaning and disinfection methods to prevent con- and the terminal dialysate samples were collected from the sample port distal to the pump tamination of dialysate lines and the terminal dialysate, Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 3 of 9 Fig. 2 IWAKI Magnet Gear Pump Model MDG‑R2. a Front plate, b gear case, and c rear plate Table 1 Composition of EverClean‑500 Category Property Principal component Sodium hydroxide, silicate salt, carboxylic acid metal chelating agent Liquid properties Alkaline Appearance Yellowish clear liquid Odor Odorless pH 11.8 ± 0.2 (100‑fold dilution) EverClean-500 is a detergency enhancer added to sodium hypochlorite. The disinfection fluid contains 800 ppm sodium hypochlorite and 0.2%(v/v) EverClean-500 a dialysis machine that was routinely used in a hospital Fig. 3 Metal corrosion on the used magnet gear pump parts made dialysis center (Sapporo, Japan). The bacteria were cul - by SUS 316. (a) Front plate and (b) gear case. Photos on the left tured in nutrient broth (Premedia, Kyokuto Pharmaceuti- and right represent the front and rear sides, respectively. “Used parts” cal, Tokyo, Japan). refers to parts of a pump that had been used routinely in a clinical environment for 10 months. The corrosion area of the used metal The P.  aeruginosa suspension at a final concentration 2 2 parts was 4.02 cm for the front plate, and 6.97 cm for the gear case of about 10  colony-forming unit (CFU)/mL used for the experiment was prepared using dialysate Kindaly 3E (Fuso Pharmaceutical Industry, Osaka, Japan) sterilized by filtration using a Sartorius Syringe Filter 17598 K with Spike‑and‑recovery testing of the pump and dialysis line a pore size of 0.45  μm (Sartorius Japan, Tokyo, Japan). using a bacterial suspension The contaminated dialysate was introduced into an The capacity of the cleaning/disinfection process used to ethylene-oxide-gas-sterilized dialysis machine with or assure sterility of the dialysate line and terminal dialysate without corroded metal parts, and circulated for 25 min. was examined by spike-and-recovery testing using a bac- Then, the flow in the pump was stopped, and the bacte - terial suspension. The experimental condition was set to rial suspension left in place for 6, 12, or 18 h to allow the simulate bacterial contamination of the dialysate occur- P. aeruginosa cells to adhere to the metal parts. The tem - ring after the morning pre-cleaning and the contami- perature of the dialysate was kept at 32 °C by calculating nated dialysate being left in the terminal dialysis machine the average internal temperature of 17 dialysis machines for certain lengths of time. after stoppage of the dialysate flow. The disinfection fluid The strain of P. aeruginosa used for the experiment was contains 800  ppm sodium hypochlorite and 0.2%(v/v) isolated from the surface of the corroded metal part of EverClean-500 (Amtec, Osaka, Japan), as shown in Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 4 of 9 Table 1 and Fig. 4. Thereafter, the pumps were disassem - samples. The Holm’s test was used to evaluate the differ - bled, the metal parts were removed, and specimens of the ences in the detection times of bacteria from the samples. terminal dialysate were collected. p < 0.05 was considered indicative of a statistically signifi - cant difference. Bacterial culture of the terminal dialysate The terminal dialysate was filtered through a 47  mm Results membrane filter with a pore size of 0.45  μm (Advan - Metal corrosion of used metal parts tech Toyo, Tokyo, Japan). Then, the filter was placed in The metal parts of a disassembled dialysis pump that had a nutrient agar medium (Eiken Chemical, Tokyo, Japan) been used routinely in an ordinary clinical environment and cultured at 37  °C for 48  h. The terminal dialysates for 10  months were removed. The corroded areas of the were sampled, and the live bacterial counts in the sam- metal parts were determined to be 4.02 c m on the front ples were measured. The minimum detection sensitivity plate and 6.97 cm on the gear case (Fig.  3). The area of was 0.05 CFU/mL, 0.1 CFU/mL, and 0.5 CFU/mL at 6 h, metal corrosion was larger on the gear case than on the 12 h, and 18 h of flow stoppage time, respectively. Then, front plate, because the metal-to-metal contact area is after cleaning and disinfection, the minimum detection larger in the gear case than in other metal parts of a dial- sensitivity of terminal dialysates was 0.05 CFU/mL. Nali- ysis pump. dixic acid cetrimide (NAC) ager (Eiken Chemical) was used for identifying P. aeruginosa. Recovery of the spiked bacteria in the terminal dialysate We measured the numbers of spiked bacteria in the ter- Recovery of bacteria from the metal parts of the dialysis minal dialysate before the lines were subjected to the pump cleaning and disinfection process (Fig.  5). The counts of To determine bacterial contamination of the metal parts, bacteria in the terminal dialysate increased as the flow the pump head was removed after or without being sub- stoppage time increased. The bacterial counts in the ter - jected to the cleaning/disinfection process, and incubated minal dialysate collected from the pump without corro- in fresh dialysate for 32  °C for 24  h for the enrichment sion of the metal parts were 0.003 ± 0.005, 6.4 ± 8.7, and culture. After incubation, the pump heads were disas- 97.3 ± 93.8  CFU/mL for flow stoppage times of 6, 12, sembled as aseptically as possible on a clean bench, and and 18  h, respectively. The bacterial counts in the ter - the metal parts were immersed in a sterile physiological minal dialysate collected from the pump showing cor- saline solution. The bacteria adhering to the metal parts rosion of the metal parts were 2.1 ± 6.5, 18.9 ± 13.1, and were released by ultrasonic treatment using an ultrasonic 147.1 ± 98.2  CFU/mL for flow stoppage times of 6, 12, homogenizer US-50 (Japan Precision Machinery, Tokyo, and 18  h, respectively. The results indicated that corro - Japan). The probe tips of the homogenizer were sterilized sion of the metal parts of the pump was associated with with alcohol and flame, and inserted into the dips of the an increased rate of bacterial contamination compared metal parts. Ultrasonic irradiation was performed at a with that on the metal parts of the pump not showing rated power of 50 W at 28 kHz for 5 s. The resulting dip corrosion. When the numbers of bacteria were measured fluids were cultured on nutrient agar (Eiken Chemical) after cleaning and disinfection of the dialysis circuit with at 37 °C for 48 h. The minimum detection sensitivity was a sodium-hypochlorite-containing reagent, no bacteria 1 CFU. were observed in the terminal dialysate collected after flow stoppage times of 6 and 12  h, irrespective of the Statistical analysis presence/absence of metal corrosion. However, after a Statistical analysis was performed using the Pharmaco flow stoppage time of 18  h, even after cleaning/disinfec - Basic software (Scientist, Tokyo, Japan). The Bonfer - tion, bacteria were detected in the dialysate specimens roni’s test or Wilcoxon’s test was used to evaluate the collected from the pump showing metal corrosion (one differences in the numbers of bacteria isolated from the out of six experiments), but not in dialysate specimens Fig. 4 Cleaning and disinfection program. Sodium hypochlorite solution supplemented with EverClean‑500 was used as the disinfectant, and a single pass at 800 ppm was used for the cleaning program. Then, the system was left filled overnight with the disinfectant at 60 ppm. Finally, the circuit was washed with water the following morning Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 5 of 9 Fig. 5 Eec ff ts of flow stoppage time and presence of metal corrosion on the sterility of the terminal dialysate before cleaning and disinfection. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. The terminal dialysates were sampled, and the live bacterial counts in the samples were measured. The minimum detection sensitivity is 0.05 CFU/mL, 0.1 CFU/mL, and 0.5 CFU/mL at 6 h, 12 h, and 18 h of flow stoppage time, respectively. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value; **p < 0.01 (Bonferroni’s test); ++ p < 0.01; and + p < 0.05. NS, not significant ( Wilcoxon’s test) collected from the pump not showing corrosion of the observed on the front plate of the pump showing metal metal parts (Fig. 6). corrosion compared with that of the pump not showing metal corrosion. Whereas no bacteria were detected on Detection of spiked bacteria on the metal parts the gear case of the pump not showing metal corrosion, of the dialysis pump bacteria were detected at 14 ± 32  CFU on the gear cases We measured the counts of live bacteria isolated from showing metal corrosion. After a flow stoppage time of the metal parts of the dialysis pumps (Fig.  7). No bacte- 18  h, even after cleaning and disinfection, live bacte- ria were observed after cleaning and disinfection on the ria were detected at 560 ± 443 and 693 ± 609  CFU from metal parts of the pump after a flow stoppage time of 6 h. the front plate and gear case of the pump without metal After a flow stoppage time of 12  h, even after cleaning corrosion, respectively. In contrast, live bacteria were and disinfection, bacteria were detected at 0.2 ± 0.4 and detected at 1004 ± 1090 and 894 ± 1037  CFU from the 0.7 ± 1.6  CFU on the front plate of the pump not show- gear case of the pumps without and with metal corro- ing and showing metal corrosion, respectively. About sion, respectively. Therefore, the count of contaminated three times more live bacteria (but not significant) were bacteria in the flow path was markedly higher after a flow Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 6 of 9 Fig. 6 Eec ff ts of flow stoppage time and presence of metal corrosion on the sterility of the terminal dialysate after cleaning and disinfection. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. Then, after cleaning and disinfection (Fig. 4), the terminal dialysates were sampled, and the live bacterial counts in the samples were measured. The minimum detection sensitivity is 0.05 CFU/mL. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value stoppage time of 18 h compared with that after 12 h, and However, bacteria were occasionally detected in the ter- the increase in count was more pronounced in the pres- minal dialysate if the flow had been stopped for 18  h or ence of corrosion of metal parts of the pump. The fre - more. quency of detection of bacteria on the metal parts was Our results suggest that the sterility of pump parts, also higher after a flow stoppage time of 18  h than that regardless of the presence or absence of metal corrosion, after a flow stoppage time of 12 h (Table 2). cannot be assured, even after cleaning and disinfection, when the flow in the pump line is stopped for more than Discussion 12  h (Fig.  6). This suggests that bacteria adhere to and To the best of our knowledge, this was the first study con - grow on the surfaces of the metal parts of the pumps. ducted to evaluate influence of metal corrosion in dialysis In particular, corrosion of metal surfaces in the pump machines on the sterility of dialysate lines and terminal was associated with an increased rate of bacterial con- dialysates by spike-and-recovery testing using bacteria. tamination of the terminal dialysate. More bacteria were The results of the study indicated that the sterility of the detected in the gear case than on the front plate because terminal dialysate can be guaranteed by conventional the gear case is located at the center of the pump, an area cleaning/disinfection with a sodium-hypochlorite-con- that is relatively poorly accessible to cleaning/disinfect- taining cleaning agent (Table  1), even if the contami- ing agents. Furthermore, the corrosion area was larger on nated dialysate is pumped on the day of treatment, if the the gear case than on the front plate (Fig.  2). In general, flow in the machine has been stopped for less than 12 h. pumps cannot be routinely disassembled for checking the Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 7 of 9 Fig. 7 Eec ff ts of flow stoppage time and presence of metal corrosion on the risk of bacterial contamination of the metal parts of the dialysis pump. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. Then, after cleaning and disinfection, as shown in Fig. 4, the pump was disassembled, the bacteria on the metal parts were released by ultrasonic exposure, and the released bacteria were counted. The minimum detection sensitivity is 1 CFU. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value. ** p < 0.01 (Bonferroni’s test). NS, not significant ( Wilcoxon’s test) sterility; therefore, the sterility of the terminal dialysate bacterial adhesion increases on the rough surfaces of cannot be assured, because the sterility of the entire the metal parts [15], elimination of metal corrosion is dialysate line cannot be checked every time. needed to suppress bacterial adhesion to the metal parts Biofilm formation is a probable mechanism of bacte - of pump. It is difficult to completely remove a biofilm rial colonization of the metal parts of a pump. It is con- after it is already formed [16]. Disassembly, cleaning, sidered to increase the risk of bacterial contamination and disinfection of the pump would be required for com- of dialysate lines. It is important to avoid biofilm forma - plete removal of the bacteria adhering to the pump. Such tion in the dialysate line to the best extent possible [13]. maintenance should be performed as aseptically as pos- Therefore, early cleaning and disinfection of the machine sible to prevent contamination from the environment. piping after treatment, and filling the stopped line with In a previous study, bacterial contamination was cleaning and disinfecting agents is important to avoid observed on the corroded metal parts of a dialysis pump bacterial growth and biofilm formation [14]. Because during clinical inspection, although no bacteria were Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 8 of 9 Table 2 Eec ff ts of flow stoppage time and the presence of Japanese Association of Clinical Engineering have not metal corrosion on number of detection times from the metal referred to the bDNA contamination [4–6]. The levels parts of bDNA in the dialysate in clinical practice are typically very low and often below the detection limit. Therefore, Metal corrosion Flow Detected Not p‑ Value stoppage times detected (12 h versus it is necessary to use a spike-and-recovery test to evalu- time (h) times 18 h) ate the removal performance of an ETRF. However, it is important to note that high levels of bDNA applied in the Absent 12 1 11 < 0.01 experiments may not accurately simulate the low levels 18 10 2 of bDNA found in dialysates in clinical practice. Despite Present 12 3 9 < 0.01 this limitation, we recommend verifying the performance 18 12 0 of an ETRF to remove bDNA by spike-and-recovery test- Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced to the ing using bDNA or bacteria. experimental circuit (Fig. 1), and stopped flow for indicated times. After the cleaning and disinfection as shown in Fig. 4, the dialysis pump was disassembled, and bacteria on 12 metal parts were released by ultrasonic Conclusions exposure. Released live bacteria were detected. **p < 0.01 (Holm’s test) Bacterial colonization rates of the metal parts were higher in pumps showing metal corrosion than in those observed in the terminal dialysate [11]. We consider the not showing corrosion. The sterility of the terminal experimental setup in the present study to be a good sim- dialysate cannot be assured, even after cleaning and dis- ulation of the situation in clinical practice. A limitation of infection, when using pumps showing corrosion of the this study was that we examined only one strain of P. aer- metal parts. Furthermore, irrespective of the presence or uginosa isolated from a hospital dialysis line. We have absence of metal corrosion, the sterility of the metal parts observed many species of glucose non-fermenting gram- of a pump cannot be assured, even after cleaning and dis- negative rods (NFGNR), so-called heterotrophic bacteria, infection, if the flow in the pump has been stopped for during clinical verifications [11]. The abilities for adhe - 12 h or more. Since metal corrosion of the pump is asso- sion, including biofilm formation, differ among bacterial ciated with an increased risk of bacterial contamination species and strains [17]. Therefore, spiking-and-recovery of the terminal dialysate even after cleaning and disinfec- experiments using other bacteria might be required in tion with a sodium-hypochlorite-containing reagent, it the future. is necessary to ensure removal of corrosion of the metal Even if live bacterial contamination is avoided by clean- parts during periodic inspections. ing and disinfection, contaminations derived from dead cells, such as endotoxin (ET) and bacterial DNA frag- ments (bDNA), could still pose a problem. ET is well Abbreviations CDDS Central dialysis fluid delivery system known as a pyrogen, which is strong inducer of inflam - CFU Colony‑forming unit matory reaction [18, 19]. bDNA also induces proinflam - ETRF Endotoxin retentive filter matory cytokines and inflammatory reactions [20, 21]. NAC Nalidixic acid cetrimide NFGNR Glucose non‑fermenting gram‑negative rods In peritoneal dialysis patients, the blood bDNA level ET Endotoxin is reported as a strong predictor of the development of bDNA Bacterial DNA fragments cardiovascular disease [22]. Contamination of dialysate PS Polysulfone PEPA Polyester polymer alloy with bDNA is known to directly affect the prognosis of dialysis patients [21, 22]. In general, an ETRF is installed Acknowledgements in dialysis machines to remove ET and bacteria in clini- The authors would like to thank Dr. Kenichi Kokubo (Kitasato University, Sagamihara, Japan), Dr. Hiroki Yabe (Seirei Christopher University, Hamamatsu, cal practice [6]. However, a report described that ET Japan), Dr. Makoto Saito (Gunma Paz University, Takasaki, Japan), and members leaks from polysulfone (PS) and polyester polymer alloy of the Department of Microbiology, Sapporo Medical University School of (PEPA) membranes with repeated cleaning and disinfec- Medicine (Sapporo, Japan) for the valuable suggestions and discussions. The authors would also like to acknowledge the technical assistance for scientific tion [23, 24]. Several reports have indicated that bDNA writing provided by tutoring program of the Japanese Society for Technology passes through dialyzers [25]. And bDNA could pass of Blood Purification. through the ETRF, and enter the bloodstream through Author contributions the dialyzer. It is important to ensure optimal sterility All authors contributed to the conception and design of the study, the critical of the dialysate before placing an ETRF. Negligible con- reading of the article for important intellectual content, and the final approval taminations of ET and bDNA should be guaranteed in of the article. MN and MO contributed to the collection and assembly of data. MN and S‑iY contributed to the analysis and interpretation of the data, and the terminal dialysate. However, there are few reports also drafting of the article. on the content of bDNA in the dialysate, and the guide- lines of the Japanese Society for Dialysis Therapy and the Funding None. Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 9 of 9 Availability of data and materials 14. Isakozawa Y, Takesawa S. A basic review of the biofilm component in the The datasets analyzed during this study are available from the corresponding dialysate plumbing system. J Kyushu Univ Health Welf. 2008;9:93–8 (in author upon reasonable request. Japanese). 15. Vanhaecke E, Remon JP, Moors N, Raes F, De Rudder D, Van Peteghem A. 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Isolation several bacteria from the corrosion confirmed pump parts in the bedside console for hemodialysis therapy. J Jpn Assoc Clin Eng Technol. 2017;61:109–15 (in Japanese). 12. Nakamura M, Okayama M, Kimura K, Shibata H, Hagiwara S, Nawa T, et al. Influence of metal pump corrosion on the contamination of terminal dialysis fluid by Pseudomonas aeruginosa. J Jpn Soc Dial Ther. 2019;52:7– 13 (in Japanese). 13. Smeets E, Kooman J, van der Sande F, Stobberingh E, Claessens P, Grave W, et al. Prevention of biofilm formation in dialysis water treatment systems. Kidney Int. 2003;63:1574–6. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Renal Replacement Therapy Springer Journals

Effects of metal corrosion in the pump of a dialysis machine on the sterility of the terminal dialysate by spike-and-recovery testing with bacteria

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Copyright © The Author(s) 2024
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2059-1381
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10.1186/s41100-024-00522-6
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Abstract

Background Dialysis units have been concerned that the corroded metal parts of pumps used in hemodialysis might not allow sterility of the pump to be ensured due to bacterial contamination, even after cleaning and disinfec‑ tion are performed after dialysis treatment. The purpose of this study was to clarify the effectiveness of the clean‑ ing/disinfection process in eliminating bacterial contamination of the dialysate in pumps with and without metal corrosion. Methods A suspension of Pseudomonas aeruginosa [10 colony‑forming unit (CFU)/mL] was introduced into pumps without or with corrosion of the metal parts, and the flow in the dialysis circuit was stopped for 6, 12, or 18 h. Then, after cleaning and disinfection of the circuit with a sodium‑hypochlorite ‑ containing reagent, the amounts of live bacteria in the terminal dialysate and on the surface of the metal parts of the pump were counted. Results Irrespective of the presence or absence of metal corrosion, bacteria were detected, even after cleaning and disinfection, on the surfaces of the pump parts that had been left in contact with the bacterial suspension for more than 12 h. However, on the surfaces of the pump parts showing metal corrosion, the bacterial numbers increased dramatically after 18 h of flow stoppage time following introduction of bacteria, and bacteria were even detected in the terminal dialysate despite cleaning/disinfection of the pump. Conclusions Corrosion of the metal parts used in pumps used for dialysis increases the risk of bacterial contamina‑ tion of not only the pump parts and flow path of the dialysis machine but also the terminal dialysate, even if cleaning/ disinfection is performed. For sterility assurance of the dialysis circuit and dialysate during routine use, it is necessary to eliminate corrosion of the metal parts of dialysis pumps during scheduled maintenance. Keywords Bacterial contamination, Sterility, Dialysate, Metal corrosion, Pseudomonas aeruginosa *Correspondence: Minoru Nakamura nakamura‑m@hus.ac.jp Full list of author information is available at the end of the article © The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecom‑ mons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 2 of 9 irrespective of the presence or absence of corrosion on Background the metal parts of dialysis pumps. Dialysis performed with good-quality dialysate improves The objective of this study was to evaluate the effec - various clinical conditions in dialysis patients [1, 2]. tiveness of cleaning and disinfection on the sterility of Including the international organization for standardiza- a dialysate line and terminal dialysate following expo- tion (ISO) [3], The Japanese Society for Dialysis Therapy sure of the dialysis circuit to a bacterial suspension for and the Japanese Association of Clinical Engineers have various lengths of time of flow stoppage. We propose proposed many updated guidelines for management and an appropriate cleaning and disinfection program using validation of dialysates [4–6]. To ensure the good quality a sodium-hypochlorite-containing reagent approved by of the dialysate, validation and management of the entire the manufacturer for maintaining optimal sterility of dialysate manufacturing process, including the dialysis the dialysate and pumps, on the basis of the results of water treatment system, central dialysis fluid delivery sys - simulation experiments conducted using pumps artifi - tem (CDDS), dialysis machine, and piping to drainage of cially polluted with P. aeruginosa. the dialysate, are necessary. Various cleaning and disin- fection methods have been studied, including the use of sodium hypochlorite, acetic acid, peracetic acid, and hot citric acid solution. High temperatures and high concen- Methods trations of these agents are required for high efficacy in Experimental circuit removing biofilm [7–10]. However, disinfecting CDDS The experimental circuit used to verify the relationship with hot water can be expensive. The manufacturer’s between bacterial contamination of the pump and risk instruction manuals recommend cleaning/disinfect- of contamination of the terminal dialysate simulated a ing with sodium hypochlorite, which is effective against part of the dialysis machine configuration (Fig.  1). An biofilm-forming bacteria [10]. However, prolonged use endotoxin retentive filter (ETRF; Nipro, Osaka, Japan) of sodium hypochlorite can cause metal corrosion. Pre- was installed ahead of the pump to avoid contamina- vious studies have shown that metal corrosion can lead tion from the environment. to increased bacterial contamination [11, 12]. However, The Iwaki Magnet Gear Pump MDG-R2 (Iwaki Co., there is limited research on the effectiveness of disinfec - Tokyo, Japan) was used as the degassing pump in the tion and cleaning for maintaining dialysate sterility when dialysis machine (Fig.  2). The metal parts, the front faced with different flow stoppage times and varying lev - plate and gear case, of the pump were made of stain- els of bacterial contamination in the presence or absence less steel SUS316. Unused new parts were used as parts of metal corrosion in the pump parts. without metal corrosion. Parts used routinely in an Herein, we focused on the relationship between metal ordinary clinical environment for 10  months were cor- corrosion on the metal parts and the risk of bacterial roded, and were used as parts showing metal corrosion contamination in the dialysis machines. According to a (Fig. 3). previous study, numerous bacteria were isolated from corroded metal parts of dialysis machines during clini- cal inspections, although no bacterial contamination was observed in the terminal dialysate samples [11]. We considered metal corrosion to be an important risk factor for bacterial contamination of the dialysate. When pump parts polluted artificially by immersion in water containing Pseudomonas  aeruginosa for 15  h were assembled into a pump in a CDDS line, bacte- rial contamination was found in the terminal dialysate from pumps assembled using corroded metal parts, but not in that from pumps assembled using parts without metal corrosion [12]. Based on these observations, we believe that it would be difficult to ensure adequate ste - rility of the terminal dialysate using the conventional Fig. 1 Experimental circuit. To verify the bacterial contamination cleaning and disinfection program when using dialysis level of the pump and the terminal dialysate, an ETRF was installed pumps assembled using metal parts showing corrosion. ahead of the pump to avoid contamination from the environment. That being said, it is also important to develop opti - Dialysate was introduced into the circuit at a flow rate of 700 mL/min, mal cleaning and disinfection methods to prevent con- and the terminal dialysate samples were collected from the sample port distal to the pump tamination of dialysate lines and the terminal dialysate, Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 3 of 9 Fig. 2 IWAKI Magnet Gear Pump Model MDG‑R2. a Front plate, b gear case, and c rear plate Table 1 Composition of EverClean‑500 Category Property Principal component Sodium hydroxide, silicate salt, carboxylic acid metal chelating agent Liquid properties Alkaline Appearance Yellowish clear liquid Odor Odorless pH 11.8 ± 0.2 (100‑fold dilution) EverClean-500 is a detergency enhancer added to sodium hypochlorite. The disinfection fluid contains 800 ppm sodium hypochlorite and 0.2%(v/v) EverClean-500 a dialysis machine that was routinely used in a hospital Fig. 3 Metal corrosion on the used magnet gear pump parts made dialysis center (Sapporo, Japan). The bacteria were cul - by SUS 316. (a) Front plate and (b) gear case. Photos on the left tured in nutrient broth (Premedia, Kyokuto Pharmaceuti- and right represent the front and rear sides, respectively. “Used parts” cal, Tokyo, Japan). refers to parts of a pump that had been used routinely in a clinical environment for 10 months. The corrosion area of the used metal The P.  aeruginosa suspension at a final concentration 2 2 parts was 4.02 cm for the front plate, and 6.97 cm for the gear case of about 10  colony-forming unit (CFU)/mL used for the experiment was prepared using dialysate Kindaly 3E (Fuso Pharmaceutical Industry, Osaka, Japan) sterilized by filtration using a Sartorius Syringe Filter 17598 K with Spike‑and‑recovery testing of the pump and dialysis line a pore size of 0.45  μm (Sartorius Japan, Tokyo, Japan). using a bacterial suspension The contaminated dialysate was introduced into an The capacity of the cleaning/disinfection process used to ethylene-oxide-gas-sterilized dialysis machine with or assure sterility of the dialysate line and terminal dialysate without corroded metal parts, and circulated for 25 min. was examined by spike-and-recovery testing using a bac- Then, the flow in the pump was stopped, and the bacte - terial suspension. The experimental condition was set to rial suspension left in place for 6, 12, or 18 h to allow the simulate bacterial contamination of the dialysate occur- P. aeruginosa cells to adhere to the metal parts. The tem - ring after the morning pre-cleaning and the contami- perature of the dialysate was kept at 32 °C by calculating nated dialysate being left in the terminal dialysis machine the average internal temperature of 17 dialysis machines for certain lengths of time. after stoppage of the dialysate flow. The disinfection fluid The strain of P. aeruginosa used for the experiment was contains 800  ppm sodium hypochlorite and 0.2%(v/v) isolated from the surface of the corroded metal part of EverClean-500 (Amtec, Osaka, Japan), as shown in Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 4 of 9 Table 1 and Fig. 4. Thereafter, the pumps were disassem - samples. The Holm’s test was used to evaluate the differ - bled, the metal parts were removed, and specimens of the ences in the detection times of bacteria from the samples. terminal dialysate were collected. p < 0.05 was considered indicative of a statistically signifi - cant difference. Bacterial culture of the terminal dialysate The terminal dialysate was filtered through a 47  mm Results membrane filter with a pore size of 0.45  μm (Advan - Metal corrosion of used metal parts tech Toyo, Tokyo, Japan). Then, the filter was placed in The metal parts of a disassembled dialysis pump that had a nutrient agar medium (Eiken Chemical, Tokyo, Japan) been used routinely in an ordinary clinical environment and cultured at 37  °C for 48  h. The terminal dialysates for 10  months were removed. The corroded areas of the were sampled, and the live bacterial counts in the sam- metal parts were determined to be 4.02 c m on the front ples were measured. The minimum detection sensitivity plate and 6.97 cm on the gear case (Fig.  3). The area of was 0.05 CFU/mL, 0.1 CFU/mL, and 0.5 CFU/mL at 6 h, metal corrosion was larger on the gear case than on the 12 h, and 18 h of flow stoppage time, respectively. Then, front plate, because the metal-to-metal contact area is after cleaning and disinfection, the minimum detection larger in the gear case than in other metal parts of a dial- sensitivity of terminal dialysates was 0.05 CFU/mL. Nali- ysis pump. dixic acid cetrimide (NAC) ager (Eiken Chemical) was used for identifying P. aeruginosa. Recovery of the spiked bacteria in the terminal dialysate We measured the numbers of spiked bacteria in the ter- Recovery of bacteria from the metal parts of the dialysis minal dialysate before the lines were subjected to the pump cleaning and disinfection process (Fig.  5). The counts of To determine bacterial contamination of the metal parts, bacteria in the terminal dialysate increased as the flow the pump head was removed after or without being sub- stoppage time increased. The bacterial counts in the ter - jected to the cleaning/disinfection process, and incubated minal dialysate collected from the pump without corro- in fresh dialysate for 32  °C for 24  h for the enrichment sion of the metal parts were 0.003 ± 0.005, 6.4 ± 8.7, and culture. After incubation, the pump heads were disas- 97.3 ± 93.8  CFU/mL for flow stoppage times of 6, 12, sembled as aseptically as possible on a clean bench, and and 18  h, respectively. The bacterial counts in the ter - the metal parts were immersed in a sterile physiological minal dialysate collected from the pump showing cor- saline solution. The bacteria adhering to the metal parts rosion of the metal parts were 2.1 ± 6.5, 18.9 ± 13.1, and were released by ultrasonic treatment using an ultrasonic 147.1 ± 98.2  CFU/mL for flow stoppage times of 6, 12, homogenizer US-50 (Japan Precision Machinery, Tokyo, and 18  h, respectively. The results indicated that corro - Japan). The probe tips of the homogenizer were sterilized sion of the metal parts of the pump was associated with with alcohol and flame, and inserted into the dips of the an increased rate of bacterial contamination compared metal parts. Ultrasonic irradiation was performed at a with that on the metal parts of the pump not showing rated power of 50 W at 28 kHz for 5 s. The resulting dip corrosion. When the numbers of bacteria were measured fluids were cultured on nutrient agar (Eiken Chemical) after cleaning and disinfection of the dialysis circuit with at 37 °C for 48 h. The minimum detection sensitivity was a sodium-hypochlorite-containing reagent, no bacteria 1 CFU. were observed in the terminal dialysate collected after flow stoppage times of 6 and 12  h, irrespective of the Statistical analysis presence/absence of metal corrosion. However, after a Statistical analysis was performed using the Pharmaco flow stoppage time of 18  h, even after cleaning/disinfec - Basic software (Scientist, Tokyo, Japan). The Bonfer - tion, bacteria were detected in the dialysate specimens roni’s test or Wilcoxon’s test was used to evaluate the collected from the pump showing metal corrosion (one differences in the numbers of bacteria isolated from the out of six experiments), but not in dialysate specimens Fig. 4 Cleaning and disinfection program. Sodium hypochlorite solution supplemented with EverClean‑500 was used as the disinfectant, and a single pass at 800 ppm was used for the cleaning program. Then, the system was left filled overnight with the disinfectant at 60 ppm. Finally, the circuit was washed with water the following morning Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 5 of 9 Fig. 5 Eec ff ts of flow stoppage time and presence of metal corrosion on the sterility of the terminal dialysate before cleaning and disinfection. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. The terminal dialysates were sampled, and the live bacterial counts in the samples were measured. The minimum detection sensitivity is 0.05 CFU/mL, 0.1 CFU/mL, and 0.5 CFU/mL at 6 h, 12 h, and 18 h of flow stoppage time, respectively. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value; **p < 0.01 (Bonferroni’s test); ++ p < 0.01; and + p < 0.05. NS, not significant ( Wilcoxon’s test) collected from the pump not showing corrosion of the observed on the front plate of the pump showing metal metal parts (Fig. 6). corrosion compared with that of the pump not showing metal corrosion. Whereas no bacteria were detected on Detection of spiked bacteria on the metal parts the gear case of the pump not showing metal corrosion, of the dialysis pump bacteria were detected at 14 ± 32  CFU on the gear cases We measured the counts of live bacteria isolated from showing metal corrosion. After a flow stoppage time of the metal parts of the dialysis pumps (Fig.  7). No bacte- 18  h, even after cleaning and disinfection, live bacte- ria were observed after cleaning and disinfection on the ria were detected at 560 ± 443 and 693 ± 609  CFU from metal parts of the pump after a flow stoppage time of 6 h. the front plate and gear case of the pump without metal After a flow stoppage time of 12  h, even after cleaning corrosion, respectively. In contrast, live bacteria were and disinfection, bacteria were detected at 0.2 ± 0.4 and detected at 1004 ± 1090 and 894 ± 1037  CFU from the 0.7 ± 1.6  CFU on the front plate of the pump not show- gear case of the pumps without and with metal corro- ing and showing metal corrosion, respectively. About sion, respectively. Therefore, the count of contaminated three times more live bacteria (but not significant) were bacteria in the flow path was markedly higher after a flow Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 6 of 9 Fig. 6 Eec ff ts of flow stoppage time and presence of metal corrosion on the sterility of the terminal dialysate after cleaning and disinfection. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. Then, after cleaning and disinfection (Fig. 4), the terminal dialysates were sampled, and the live bacterial counts in the samples were measured. The minimum detection sensitivity is 0.05 CFU/mL. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value stoppage time of 18 h compared with that after 12 h, and However, bacteria were occasionally detected in the ter- the increase in count was more pronounced in the pres- minal dialysate if the flow had been stopped for 18  h or ence of corrosion of metal parts of the pump. The fre - more. quency of detection of bacteria on the metal parts was Our results suggest that the sterility of pump parts, also higher after a flow stoppage time of 18  h than that regardless of the presence or absence of metal corrosion, after a flow stoppage time of 12 h (Table 2). cannot be assured, even after cleaning and disinfection, when the flow in the pump line is stopped for more than Discussion 12  h (Fig.  6). This suggests that bacteria adhere to and To the best of our knowledge, this was the first study con - grow on the surfaces of the metal parts of the pumps. ducted to evaluate influence of metal corrosion in dialysis In particular, corrosion of metal surfaces in the pump machines on the sterility of dialysate lines and terminal was associated with an increased rate of bacterial con- dialysates by spike-and-recovery testing using bacteria. tamination of the terminal dialysate. More bacteria were The results of the study indicated that the sterility of the detected in the gear case than on the front plate because terminal dialysate can be guaranteed by conventional the gear case is located at the center of the pump, an area cleaning/disinfection with a sodium-hypochlorite-con- that is relatively poorly accessible to cleaning/disinfect- taining cleaning agent (Table  1), even if the contami- ing agents. Furthermore, the corrosion area was larger on nated dialysate is pumped on the day of treatment, if the the gear case than on the front plate (Fig.  2). In general, flow in the machine has been stopped for less than 12 h. pumps cannot be routinely disassembled for checking the Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 7 of 9 Fig. 7 Eec ff ts of flow stoppage time and presence of metal corrosion on the risk of bacterial contamination of the metal parts of the dialysis pump. Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced into the experimental circuit (Fig. 1), and the circuit flow was stopped for the indicated periods. Then, after cleaning and disinfection, as shown in Fig. 4, the pump was disassembled, the bacteria on the metal parts were released by ultrasonic exposure, and the released bacteria were counted. The minimum detection sensitivity is 1 CFU. ● indicates not detected; ○ indicates detected; and the dashed lines indicate mean value. ** p < 0.01 (Bonferroni’s test). NS, not significant ( Wilcoxon’s test) sterility; therefore, the sterility of the terminal dialysate bacterial adhesion increases on the rough surfaces of cannot be assured, because the sterility of the entire the metal parts [15], elimination of metal corrosion is dialysate line cannot be checked every time. needed to suppress bacterial adhesion to the metal parts Biofilm formation is a probable mechanism of bacte - of pump. It is difficult to completely remove a biofilm rial colonization of the metal parts of a pump. It is con- after it is already formed [16]. Disassembly, cleaning, sidered to increase the risk of bacterial contamination and disinfection of the pump would be required for com- of dialysate lines. It is important to avoid biofilm forma - plete removal of the bacteria adhering to the pump. Such tion in the dialysate line to the best extent possible [13]. maintenance should be performed as aseptically as pos- Therefore, early cleaning and disinfection of the machine sible to prevent contamination from the environment. piping after treatment, and filling the stopped line with In a previous study, bacterial contamination was cleaning and disinfecting agents is important to avoid observed on the corroded metal parts of a dialysis pump bacterial growth and biofilm formation [14]. Because during clinical inspection, although no bacteria were Nakamura et al. Renal Replacement Therapy (2024) 10:6 Page 8 of 9 Table 2 Eec ff ts of flow stoppage time and the presence of Japanese Association of Clinical Engineering have not metal corrosion on number of detection times from the metal referred to the bDNA contamination [4–6]. The levels parts of bDNA in the dialysate in clinical practice are typically very low and often below the detection limit. Therefore, Metal corrosion Flow Detected Not p‑ Value stoppage times detected (12 h versus it is necessary to use a spike-and-recovery test to evalu- time (h) times 18 h) ate the removal performance of an ETRF. However, it is important to note that high levels of bDNA applied in the Absent 12 1 11 < 0.01 experiments may not accurately simulate the low levels 18 10 2 of bDNA found in dialysates in clinical practice. Despite Present 12 3 9 < 0.01 this limitation, we recommend verifying the performance 18 12 0 of an ETRF to remove bDNA by spike-and-recovery test- Dialysate spiked with P. aeruginosa (10 CFU/mL) was introduced to the ing using bDNA or bacteria. experimental circuit (Fig. 1), and stopped flow for indicated times. After the cleaning and disinfection as shown in Fig. 4, the dialysis pump was disassembled, and bacteria on 12 metal parts were released by ultrasonic Conclusions exposure. Released live bacteria were detected. **p < 0.01 (Holm’s test) Bacterial colonization rates of the metal parts were higher in pumps showing metal corrosion than in those observed in the terminal dialysate [11]. We consider the not showing corrosion. The sterility of the terminal experimental setup in the present study to be a good sim- dialysate cannot be assured, even after cleaning and dis- ulation of the situation in clinical practice. A limitation of infection, when using pumps showing corrosion of the this study was that we examined only one strain of P. aer- metal parts. Furthermore, irrespective of the presence or uginosa isolated from a hospital dialysis line. We have absence of metal corrosion, the sterility of the metal parts observed many species of glucose non-fermenting gram- of a pump cannot be assured, even after cleaning and dis- negative rods (NFGNR), so-called heterotrophic bacteria, infection, if the flow in the pump has been stopped for during clinical verifications [11]. The abilities for adhe - 12 h or more. Since metal corrosion of the pump is asso- sion, including biofilm formation, differ among bacterial ciated with an increased risk of bacterial contamination species and strains [17]. Therefore, spiking-and-recovery of the terminal dialysate even after cleaning and disinfec- experiments using other bacteria might be required in tion with a sodium-hypochlorite-containing reagent, it the future. is necessary to ensure removal of corrosion of the metal Even if live bacterial contamination is avoided by clean- parts during periodic inspections. ing and disinfection, contaminations derived from dead cells, such as endotoxin (ET) and bacterial DNA frag- ments (bDNA), could still pose a problem. ET is well Abbreviations CDDS Central dialysis fluid delivery system known as a pyrogen, which is strong inducer of inflam - CFU Colony‑forming unit matory reaction [18, 19]. bDNA also induces proinflam - ETRF Endotoxin retentive filter matory cytokines and inflammatory reactions [20, 21]. NAC Nalidixic acid cetrimide NFGNR Glucose non‑fermenting gram‑negative rods In peritoneal dialysis patients, the blood bDNA level ET Endotoxin is reported as a strong predictor of the development of bDNA Bacterial DNA fragments cardiovascular disease [22]. Contamination of dialysate PS Polysulfone PEPA Polyester polymer alloy with bDNA is known to directly affect the prognosis of dialysis patients [21, 22]. In general, an ETRF is installed Acknowledgements in dialysis machines to remove ET and bacteria in clini- The authors would like to thank Dr. Kenichi Kokubo (Kitasato University, Sagamihara, Japan), Dr. Hiroki Yabe (Seirei Christopher University, Hamamatsu, cal practice [6]. However, a report described that ET Japan), Dr. Makoto Saito (Gunma Paz University, Takasaki, Japan), and members leaks from polysulfone (PS) and polyester polymer alloy of the Department of Microbiology, Sapporo Medical University School of (PEPA) membranes with repeated cleaning and disinfec- Medicine (Sapporo, Japan) for the valuable suggestions and discussions. The authors would also like to acknowledge the technical assistance for scientific tion [23, 24]. Several reports have indicated that bDNA writing provided by tutoring program of the Japanese Society for Technology passes through dialyzers [25]. And bDNA could pass of Blood Purification. through the ETRF, and enter the bloodstream through Author contributions the dialyzer. It is important to ensure optimal sterility All authors contributed to the conception and design of the study, the critical of the dialysate before placing an ETRF. Negligible con- reading of the article for important intellectual content, and the final approval taminations of ET and bDNA should be guaranteed in of the article. MN and MO contributed to the collection and assembly of data. MN and S‑iY contributed to the analysis and interpretation of the data, and the terminal dialysate. However, there are few reports also drafting of the article. on the content of bDNA in the dialysate, and the guide- lines of the Japanese Society for Dialysis Therapy and the Funding None. Nak amura et al. Renal Replacement Therapy (2024) 10:6 Page 9 of 9 Availability of data and materials 14. Isakozawa Y, Takesawa S. A basic review of the biofilm component in the The datasets analyzed during this study are available from the corresponding dialysate plumbing system. J Kyushu Univ Health Welf. 2008;9:93–8 (in author upon reasonable request. Japanese). 15. Vanhaecke E, Remon JP, Moors N, Raes F, De Rudder D, Van Peteghem A. Kinetics of Pseudomonas aeruginosa adhesion to 304 and 316‑L stain‑ Declarations less steel: role of cell surface hydrophobicity. Appl Environ Microbiol. 1990;56:788–95. Ethics approval and consent to participate 16. Cappelli G, Ballestri M, Perrone S, Ciuffreda A, Inguaggiato P, Albertazzi Not applicable. A. Biofilms invade nephrology: effects in hemodialysis. Blood Purif. 2000;18:224–30. Consent for publication 17. Matsuoka T. Biology of biofilms. Microbes Environ. 1999;14:163–72. Not applicable. 18. Michie HR, Manogue KR, Spriggs DR, Revhaug A, O’Dwyer S, Dinarello CA, et al. Detection of circulating tumor necrosis factor after endotoxin Competing interests administration. N Engl J Med. 1988;318:1481–6. The authors declare that they have no competing interests. 19. Giovanni P, Giuseppe G, Loreto G, Francesco PS. Clinical relevance of production in hemodialysis. Kidney Int. 2000;58(Suppl. 76):S104–11. Author details 20. 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Journal

Renal Replacement TherapySpringer Journals

Published: Feb 2, 2024

Keywords: Bacterial contamination; Sterility; Dialysate; Metal corrosion; Pseudomonas aeruginosa

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