Changing trend in bile microbiology and antibiotic susceptibilities: over 12 years of experience

Rapidly changing medical environments may have changed the microbiology of infected bile. The aim of our study was to identify the changing trends in microorganisms in biliary infections and examine their susceptibilities against currently recommended antibiotics.

Bile cultures taken between 1998 and 2010 at Seoul National University Hospital, a tertiary medical center, were retrospectively reviewed. From 1,403 patients, 3,425 microorganisms were isolated from 2,217 cultures. The cultures were then tested to determine the types of microorganisms and their antibiotic susceptibility.

The five most frequently isolated microorganisms were Enterococcus (22.7 %) followed by Escherichia (13.2 %), Pseudomonas (10.9 %), Klebsiella (10.3 %), and Enterobacter (7.2 %). The trend in annual incidence indicated a growing emergence of Enterococcus (P < 0.001). Among Enterococcus, E. faecium acquired a dominant position (50.6 %), showing an increasing trend over the study period (P = 0.026). The incidence of vancomycin-resistant Enterococcus also showed an increasing trend (P < 0.001). Many of the commonly used antibiotics provided inadequate coverage for the more frequently encountered microorganisms. Multiple regression revealed that benign causes of obstruction and non-operative treatment harbor an increased risk for enterococcal growth (P = 0.001 and P = 0.027, respectively).

In contrast to earlier reports, we found that Enterococcus has emerged as the most frequently isolated microorganism from bile. The importance of enterococcal infection should be recognized, and currently recommended antibiotics need to be re-evaluated since in our bile cultures most provided inadequate coverage for the more frequently encountered microorganisms. The changes in the trends of microorganisms isolated from bile should be considered in cases where patients present with biliary obstruction.