Phenotypic and genotypic characterization of carbapenem resistance mechanisms in Klebsiella pneumoniae from blood culture specimens: A study from North India.

BACKGROUND: Emergence of carbapenem resistance among Enterobacteriaceae in different geographical regions is of great concern as these bacteria are easily transmissible among patients. Carbapenem-resistance in Enterobacteriaceae is due to production of carbapenemases of various classes and hyper production of the ESBLs (Extended spectrum beta lactamases) and Amp C beta lactamases with reduced cell wall permeability mechanisms. Phenotypic detection and differentiation is important for proper infection control and appropriate patient management. This study was done to know the prescence of various beta lactamases and carbapenemases with other mechanisms of resistance in Klebsiella pneumoniae isolates.

MATERIALS AND METHODS: 50 non-duplicate carbapenem resistant isolates of Klebsiella pneumoniae from blood culture specimens were included and various mechanisms of resistance were studied based on phenotypic and genotypic methods.

RESULTS: Out of 50 isolates, 39 (78%) of K. pneumoniae isolates were Extended Spectrum Beta Lactamase (ESBL) producers based on CLSI guidelines. All 50 showed positive Modified Hodge Test (MHT) and 32 showed Metallo Beta Lactamase (MBL) by Combined Disc Test (CDT). Four isolates showed AmpC production with porin loss. None of the isolates showed Class A KPC production by CDT. In our study all the 10 isolates evaluated by genotypic technique produced CTX-M group 1 enzyme by multiplex PCR. Seven out of 10 strains which showed positive MBL results were positive for NDM.

CONCLUSIONS: Carbapenems are often considered last resort antibiotics in the treatment of infections due to multidrug-resistant organisms. It is therefore mandatory to maintain the clinical efficacy of carbapenems by early detection of various enzymes. For routine clinical laboratories both phenotypic and genotypic tests need to be followed to detect various mechanisms of carbapenem resistance and this is of epidemiological relevance also.