The role of Enterococcus spp. and multidrug-resistant bacteria causing pyogenic liver abscesses

Background: Pyogenic liver abscesses (PLA) remain a significant clinical problem. Unfortunately, little is known about current bacterial susceptibility profiles and the incidence of multidrug resistant organisms (MDROs) causing PLA in Western countries. Yet, this crucial information is pivotal to guide empirical antibiotic therapy. Aim of this study was to provide detailed characteristics of PLA with a special focus on underlying bacterial pathogens and their susceptibility to antibiotics. Methods: A retrospective study of patients diagnosed with PLA from 2009 to 2015 in a large tertiary reference center in Germany was performed in order to characterize PLA and antimicrobial susceptibility profiles of causative bacterial species. Results: Overall, 86 patients were included. The most common causes of PLA were bile duct stenosis/obstruction (31.4%) and leakage of biliary anastomosis (15.1%). Frequent predisposing diseases were malignancies (34.9%), diabetes (24.4%) and the presence of liver cirrhosis (16.3%). Of note, Enterococcus spp. were the most frequently cultured bacterial isolates (28.9%), and in 1/3 of cases vancomycin resistance was observed. In addition, a relevant frequency of gram-negative MDROs was identified. In particular, an alarming 10% and 20% of gram-negative bacteria were resistant to carbapenems and tigecycline, respectively Of note, MDRO status did not predict ICU stay or survival in multivariate regression analysis. The mortality rate in our series was 16.3%. Conclusion: Our study demonstrates an as yet underreported role of Enterococcus spp., often associated with vancomycin resistance, as well as of gram-negative MDROs causing PLA.