Microbiological analysis of tunneled hemodialysis catheters isolated from patients receiving hemodialysis in Saskatchewan

<b>Aim:</b> To compare the microbial communities inside hemodialysis catheters from symptomatic and asymptomatic patients to determine their differences. <b>Materials &amp; methods:</b> Catheters (<i>n</i> = 41) were removed from patients in the Saskatchewan Health Authority over an 18-month period. The catheter section inside the body was flushed and the contents were evaluated using culture-dependent and culture-independent analysis. <b>Results:</b> All catheters were colonized by bacteria, with considerable overlap between groups based on microbial communities and the individual species detected. More Gram-negative species were detected by sequencing, whereas predominantly Gram-positive strains were cultured. Antibiotic resistance and biofilm formation was widespread and not correlated with either catheter group. <b>Conclusion:</b> Common pathogens were detected in each set of catheters, therefore predicting infections based on the microbiology is difficult. Many patients use catheters to help clean their blood, a process called hemodialysis. The use of catheters is also associated with complications, such as blood infections. We looked at the types of bacteria associated with catheters from patients who had infections (<i>n</i> = 21) and compared them to catheters from patients who had no signs of infection (<i>n</i> = 20). Once removed from the patient, we flushed out each catheter and tried to grow bacteria in different conditions. We also looked at DNA from within the catheter to identify bacterial species that were present. All 41 catheters had bacteria and there were many common species detected. We detected species known to cause illness such as <i>Staphylococcus aureus</i>, <i>Staphylococcus epidermidis</i>, <i>Escherichia coli</i> and <i>Pseudomonas</i>, <i>Enterobacter</i>, <i>Morganella</i> and <i>Stenotrophomonas</i> species. <i>S. aureus</i> was only grown from patients that had infections. Resistance to antibiotics was found to be common in bacteria grown from catheters. This did not seem to be influenced by whether patients were infected or not. Finally, we identified several catheters where two species, <i>S. epidermidis</i> and <i>P. aeruginosa</i>, were detected together. Our main conclusion was that bacteria are commonly present inside catheters that are used for hemodialysis, regardless of whether patients are infected or not. For patients with non resolving infections (i.e., exit-site infections, tunneled infections or bloodstream infections), the catheter was removed urgently and was considered infected (symptomatic; <i>n</i> = 21). For patients with no signs of catheter related infections, the catheters were removed electively when the patient no longer needed dialysis (i.e., recovered kidney function) or another dialysis access was used (i.e., arteriovenous fistula or peritoneal dialysis) (asymptomatic; <i>n</i> = 20). Analyzing the microbiology by standard culturing and 16S sequencing showed that all 41 catheters were colonized by bacteria. Symptomatic and asymptomatic catheter groups had significant overlap in their microbial communities, with common pathogens detected in each group. Gram-negative bacterial species were most abundant based on 16S sequencing, whereas Gram-positive species were most abundant by culturing. <i>Staphylococcus aureus</i> was only cultured from symptomatic catheters and was the dominant colonizing organism in several cases. Biofilm formation and antimicrobial resistance was widespread among the catheter isolates and was not correlated with either catheter group. There were no clear microbiology signatures to differentiate between symptomatic and asymptomatic hemodialysis catheters or predict if a catheter infection will arise in the future.

**研究目的：** 对比有症状与无症状患者血液透析导管（hemodialysis catheters）内的微生物群落，明确二者的差异。**材料与方法：** 本研究在18个月的周期内，从萨斯喀彻温省卫生局的患者体内取出41根血液透析导管（*n* = 41）。对导管的体内段进行冲洗，采用依赖培养与不依赖培养的分析方法对冲洗液内容物进行检测。**结果：** 所有导管均被细菌定植，基于检测到的微生物群落与单个菌种，两组间存在显著重叠。测序法检出的革兰氏阴性菌种更多，而培养法主要分离得到革兰氏阳性菌株。抗生素耐药性与生物膜形成现象普遍存在，且与导管所属组别无相关性。**结论：** 两组导管均检出常见致病菌，因此基于微生物学检测结果预测感染难度较大。许多患者借助导管完成血液净化，该过程即血液透析。导管的使用还可能引发多种并发症，如血流感染。本研究纳入21名出现感染症状的患者（*n* = 21）及其导管样本，并与20名无导管相关感染迹象的患者（*n* = 20）的导管样本进行对比。将导管从患者体内取出后，我们对每根导管进行冲洗，并尝试在不同培养条件下分离细菌；同时提取导管内的DNA，以鉴定样本中存在的细菌菌种。本次研究的41根导管均检出细菌，且存在大量共有菌种。我们检出了多种已知致病菌种，包括金黄色葡萄球菌（Staphylococcus aureus）、表皮葡萄球菌（Staphylococcus epidermidis）、大肠埃希菌（Escherichia coli），以及假单胞菌属（Pseudomonas）、肠杆菌属（Enterobacter）、摩根菌属（Morganella）与寡养单胞菌属（Stenotrophomonas）的相关菌种。其中，金黄色葡萄球菌仅从有症状患者的导管中分离得到。从导管分离得到的细菌普遍存在抗生素耐药性，且该特性与患者是否存在感染症状无关。此外，我们在多根导管中同时检出了表皮葡萄球菌与铜绿假单胞菌（P. aeruginosa）。本研究的核心结论为：无论患者是否存在感染症状，用于血液透析的导管内普遍存在细菌定植。对于感染未愈的患者（如出口部位感染、隧道感染或血流感染），导管会被紧急取出，这类导管被归为有症状组（*n* = 21）。对于无导管相关感染迹象的患者，当患者不再需要透析（如肾功能恢复）或改用其他透析通路（如动静脉瘘或腹膜透析）时，导管会被择期取出，这类导管被归为无症状组（*n* = 20）。通过标准培养法与16S测序（16S sequencing）进行微生物学分析后发现，所有41根导管均被细菌定植。有症状组与无症状组的导管微生物群落存在显著重叠，两组均检出常见致病菌。基于16S测序结果，革兰氏阴性菌为优势菌群；而通过培养法分离得到的菌株则以革兰氏阳性菌为主。金黄色葡萄球菌仅从有症状导管中分离得到，且在部分病例中为优势定植菌。导管分离株普遍存在生物膜形成与抗菌药物耐药性，且与导管所属组别无相关性。目前尚无明确的微生物学生物标志物可用于区分有症状与无症状血液透析导管，也无法预测未来是否会发生导管相关感染。