Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Porin defects and carbapenem resistance in Klebsiella pneumoniae (#141)

Alex Agyekum 1 , Alicia Fajardo-Lubian 1 , Sally Partridge 1 , Jon Iredell 1
  1. Centre for Research Excellence in Critical Infection, Westmead Millennium Institute, Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney, Sydney, NSW, Australia
Klebsiella pneumoniae is a leading cause of hospital acquired infection such as pneumonia, they are resistant to almost all antibiotics including the carbapenems which are often regarded as antibiotic of ʽlast resortʼ in critical infections. The aim of this study was to investigate the natural MIC distribution of β-lactam resistance phenotypes and the molecular mechanisms of carbapenem resistance in Klebsiella pneumoniae in Sydney, Australia. A total of 180 clinical isolates, with relevant transmissible resistance genes (plasmid AmpC, n=28; Extended spectrum β-lactamase, n=72 or carbapenemase, n=50), were characterised. Thirty Klebsiella pneumoniae isolates with no phenotypic resistance to any antibiotics tested and none of the important β-lactam genes were also included as controls. The minimal inhibitory concentrations (MIC) of five β-lactam antibiotics (cefotaxime, ceftazidime, imipenem, meropenem and ertapenem) against these isolates were found to be normally distributed in the bacterial population, except ertapenem. We found a high prevalence of ETP non-susceptibility among the blaCTX-M isolates (20/72, 28%) and this was due to the combination of the ESBL gene with an OmpK36 defect. Sequencing of ompK36 genes and sodium dodecyl-sulphate-polyacrylamide gel electrophoresis demonstrated loss or mutations in the ompK36 gene in all isolates with reduced susceptibility to ertapenem (MIC >1 mg/l) in the absence of known “carbapenemase” genes (n=23). This means that a porin (particularly, OmpK36) -defective K. pneumoniae strain may become carbapenem non-susceptible upon acquisition of ordinary ESBL genes. For this reason, it is crucial to detect these mutations in K. pneumoniae strains to ensure the success of antimicrobial therapy.