Avaliação de heterorresistência ao imipenem em enterobactérias produtoras e não-produtoras de kpc

Abstract

The misdetection of Klebsiella pneumoniae carbapenemase (KPC) may lead to treatment failure and favour the spread of this resistance mechanism. Heteroresistance is an antimicrobial resistance in a subset of an isolate considered to be susceptible by conventional testing. The aim of this study was to evaluate the presence of heteroresistance to imipenem in KPC-producing and non-producing K. pneumoniae and E. coli. After the determination of the minimum inhibitory concentration (MIC) to imipenem by broth microdilution, each isolate with MIC lower than 4 mg L-1 was subcultured in plates containing imipenem ranging from 0.25 mg L-1 to 32 mg L-1. Isolates with growth in imipenem concentrations two fold dilutions above the original MIC were considered heteroresistant. The KPC group consisted of 10 isolates, while the non-KPC group consisted of four isolates and distinct results were observed among them: all KPC-producing isolates presented heteroresistance to imipenem, while for the KPC-non-producing isolates this phenomenon was not observed. Interestingly, we also found heteroresistance in E. coli isolates, which, to best of our knowledge, was not reported as yet. Our results indicated a possible relationship between heteroresistance and KPC production. The clinical implications of appearing of heteroresistant subpopulations remains to be investigated, considering that this phenomenon seems to be frequent in Gram-negative rods, including members, such as E. coli, in which this phenomenon is still rarely investigated.