Epidemiology and Resistance Patterns of Bacterial and Fungal Colonization of Biliary Plastic Stents: A Prospective Cohort Study

Abstract

Background: Plastic stents used for the treatment of biliary obstruction will become occluded over time due to microbial colonization and formation of biofilms. Treatment of stent-associated cholangitis is often not effective because of inappropriate use of antimicrobial agents or antimicrobial resistance. We aimed to assess the current bacterial and fungal etiology of stent-associated biofilms, with particular emphasis on antimicrobial resistance.

Methods: Patients with biliary strictures requiring endoscopic stent placement were prospectively enrolled. After the retrieval of stents, biofilms were disrupted by sonication, microorganisms were cultured, and isolates were identified by matrix-associated laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and/or biochemical typing. Finally, minimum inhibitory concentrations (MICs) were determined for various antimicrobial agents. Selected stents were further analyzed by fluorescence in situ hybridization (FISH).

Results: Among 120 patients (62.5% males, median age 64 years) with biliary strictures (35% malignant, 65% benign), 113 double pigtail polyurethane and 100 straight polyethylene stents were analyzed after a median indwelling time of 63 days (range, 1-1274 days). The stent occlusion rate was 11.5% and 13%, respectively, being associated with a significantly increased risk of cholangitis (38.5% vs. 9.1%, P<0.001). Ninety-five different bacterial and 13 fungal species were detected; polymicrobial colonization predominated (95.8% vs. 4.2%, P<0.001). Enterococci (79.3%), Enterobacteriaceae (73.7%), and Candida spp. (55.9%) were the leading pathogens. Candida species were more frequent in patients previously receiving prolonged antibiotic therapy (63% vs. 46.7%, P = 0.023). Vancomycin-resistant enterococci accounted for 13.7%, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae with co-resistance to ciprofloxacin accounted for 13.9%, and azole-resistant Candida spp. accounted for 32.9% of the respective isolates.

Conclusions: Enterococci and Candida species play an important role in the microbial colonization of biliary stents. Therefore, empirical antimicrobial treatment of stent-associated cholangitis should be guided toward enterococci, Enterobacteriaceae, streptococci, anaerobes, and Candida. To determine causative pathogens, an accurate microbiological analysis of the extracted stent(s) may be helpful.

Fig 1. Endoscopic extraction of occluded biliary polyethylene stents (double stenting in a 52 year-old patient with biliary stenosis due to chronic pancreatitis).

Fig 2. Presence of biofilm formation on a biliary polyethylene stent in a 62-year-old liver transplant recipient with anastomotic bile duct stenosis, visualized by fluorescence in situ hybridization (FISH).

Using cultures, Enteroccus faecalis and Escherichia coli were detected.

Fig 3. Overview of microbiological results of cultures from sonicated stent fluids.

Polymicrobial colonization of biliary stents (95.8%) was significantly more common than single microbial colonization (4.2%, P <0.001) was.

Fig 4. Scatter plot of stent duration in place (in days) vs. number of detected microorganisms.

Fig 5. Stent duration in place (in days) versus microbiological isolates from sonicated stent fluids, grouped by predominant enterococci, Enterobacteriaceae, Candida spp., and streptococci.

Fig 6. Distribution of bacterial and fungal species depending on the use of antibiotics.

Stent colonization differed significantly with respect to the proportion of Candida species (46.7% vs. 63%, P = 0.023) in patients receiving prolonged antibiotic therapy.

Fig 7. In vitro antibiotic susceptibilities of bacterial and fungal isolates, grouped by Enterococcus faecalis, Enterococcus faecium, streptococci, Escherichia coli, Candida albicans, and non-albicans Candida (NAC) species.

Minimum inhibitory concentrations (MICs) were determined employing Industrial Organization for Standardization (ISO) 20766–1 or E-test, and the results were interpreted according to current European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints (www.eucast.org, 2015 edition).