An outbreak of ertapenem resistant, carbapenemase-negative and porin-deficient ESBL-producing Klebsiella pneumoniae complex

Introduction: Carbapenem-resistant Klebsiella pneumoniae is an emerging healthcare-associated pathogen with dynamic molecular epidemiology. This study presents a retrospective analysis of the distribution and antibiotic resistance patterns of ertapenem-resistant ESBL-producing K. pneumoniae strains recovered during an outbreak from 2012 to 2014 in a Croatian University hospital. Methods We aimed to estimate genetic relatedness of clinical isolates and underlying mechanisms that conferred the ertapenem- resistant phenotype. Results: Expression analysis of genes involved in the antibiotic resistance showed reduced expression of major non-selective porin channel OmpK35. Reduced expression of OmpK36 porin channel in isolates resistant to at least one more carbapenem, apart from the ertapenem, was found to a lesser degree. Pulsed-field gel electrophoresis analysis of genomic DNA revealed that almost all isolates belonged to the same genetic clone. Conclusions: Caution regarding ertapenem- resistant, carbapenemase-negative porin- deficient mutants of K. pneumoniae is required as they are widespread, and under selective pressure this could result in a local clonal outbreak.