Carbapenem resistance mechanisms among blood isolates of Klebsiella pneumoniae and Escherichia coli

The purpose of this study was to characterize the different mechanisms of carbapenem resistance among blood isolates of Klebsiella pneumoniae and Escherichia coli. Meropenem resistant isolates were included. Antimicrobial susceptibility testing, phenotypic and genotypic detection of carbapenemase production were performed. Genetic relatedness of blaNDM-1 producers was determined by pulsed-filed gel electrophoresis (PFGE) typing. The relatedness of blaNDM-1 carrying plasmids was studied by plasmid restriction fragment length polymorphisms (pRFLP) and polymerase chain reaction (PCR) based replicon typing (PBRT). For the carbapenem gene negative isolates, other possible mechanism of carbapenem resistance such as role of outer membrane porin loss with ESBL or AmpC production, and efflux pumps were analyzed. Among the 162 isolates studied, 1 (0.6%) was found to be blaKPC-3 producer and 42.5% were blaNDM-1 producers. All the isolates were multidrug resistant; two isolates carried both blaNDM-1 and blaVIM-2. PFGE determined blaNDM-1 producers were non-related. The plasmids harbouring blaNDM-1belonged to two major incompatibility plasmid types, IncL/M and IncA/C. IncL/M is a novel plasmid group reported firstly from this region. A clonal outbreak of blaIMP-1 K. pneumoniae was identified during this study. This is the first report on the emergence of K. pneumoniae producing blaIMP-1 from South India and blaKPC-3 from India. The study suggest including ertapenem in the routine susceptibility screening to find the true rate of KPC producers in Indian hospitals. Colistin and tigecycline are two drugs that have activity but both have developed resistance. Selection of an appropriate initial antibiotic regimen for empiric therapy, rotation of different antibiotic classes and judicious use of antibiotics are essential.