Abstract
BACKGROUND & OBJECTIVES: Carbapenemase-producing Acinetobacter baumannii (CRAB) poses a continuous threat to the current antimicrobial era with its alarming spread in critical care settings. The present study was conducted to evaluate the diagnostic potential of phenotypic methods for carbapenemase [carbapenem-hydrolyzing class D β-lactamases (CHDLs) and metallo-β-lactamases (MBLs)] production, by comparing with molecular detection of genes. METHODS: One hundred and fifty clinical CRAB isolates collected between August 2013 and January 2014 were studied. Multiplex PCR was performed to identify the carbapenemases produced (class D bla(OXA-51), bla(OXA-23), bla(OXA-48,) bla(OXA-58); class B bla(VIM), bla(NDM-1), bla(IMP); class A bla(KPC)). Each isolate was evaluated for carbapenemase production by studying the pattern of imipenem hydrolysis using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). RESULTS: The most commonly encountered carbapenemase genes were bla(OXA-51)(100%), bla(OXA-23)(98%), bla(VIM)(49.3%), bla(NDM-1)(18.7%) and bla(OXA-58)(2%). MALDI-TOF MS was able to detect 30.6 per cent carbapenemases within three hours (P=0.001 for MBL and P>0.05 for CHDL) and 65.3 per cent within six hours (P=0.001 for MBL and P>0.05 for CHDL). INTERPRETATION & CONCLUSIONS: MALDI-TOF MS reliably detected carbapenemase activity within a short span of time, thus helping in tailoring patient therapy. MALDI-TOF MS, once optimized, can prove to be a useful tool for timely detection of carbapenemase production by A. baumannii and consequently in directing appropriate antimicrobial therapy.