Hypermucoviscosity, rmpA, and aerobactin are associated with community-acquired Klebsiella pneumoniae bacteremic isolates causing liver abscess in Singapore

Introduction: This retrospective study investigated the clinical etiology of community-acquired bacteremic Klebsiella pneumoniae infections, and characterized laboratory and genetic markers which may be associated with primary liver abscess (PLA). Methods: Community-onset K. pneumoniae bacteremic episodes from 2010 to 2011 were identified from the laboratory information system. Isolates were retrieved for susceptibility testing, hypermucoviscosity testing, PCR-based serotyping (K1, K2 and K5) and PCR detection of virulence genes (rmpA, ails, kfu and aerobactin). Clinical data collected from electronic medical records included primary and secondary diagnoses, co-existing morbidities, antibiotic therapy, and in-patient mortality. Results: 129 bacteremic episodes were identified. The most common primary infections were pneumonia (n = 24, 18.6%), primary liver abscess (n = 21, 16.3%) and urinary tract infections (n = 21, 16.3%). Hypermucoviscosity was present in 55 isolates (42.6%). The most commonly detected virulence genes were aerobactin (n = 63, 48.8%) and rmpA (n = 59, 45.7%). Isolates causing liver abscess were significantly associated with a positive string test, rmpA, aerobactin gene, and capsular serotype K1 (all p < 0.01), but not with capsular serotype K2, K5, kfu, or allS genes. The absence of a positive string test, rmpA, or aerobactin genes had a 97.3%-100% negative predictive value for PLA. The positive predictive values of the string test, rmpA, aerobactin genes, and serotype K1 for PLA ranged from 31.7% to 35.6%. Conclusion: In our study population, pneumonia and PLA were the most common sources of community-acquired bacteremia. Hypermucoviscosity, rmpA, aerobactin, and serotype K1 could be useful laboratory markers to alert clinicians to arrange abdominal imaging to detect liver abscess. Copyright (C) 2017, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC.