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NJBMS - Volume 7, Issue 2, October - December 2016

Pages: 106-112
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Comparison Of Phenotypic And Genotypic Methods For The Detection Of Imipenem Resistant Enterobacteriaceae Isolates

Author: C.Anuradha, S .Mathavi, R.Indra Priyadharsini,

Category: Microbiology


INTRODUCTION : The rapid spread of metallobetalactamases (MBL) is a diagnostic challenge in clinical microbiology as there are concerns regarding the reliability of the various phenotypic detection methods.

AIMS AND OBJECTIVES : To assess the efficiency of the phenotypic assays namely the combined disc test (CDT), double disc synergy test (DDST) and the MBL E test as compared to PCR for the detection of MBLs in enterobacteriaceae.

MATERIALS AND METHODS: Two hundred and four non-repetitive enterobacteriaceae isolates from clinical samples from October 2013 to September 2014 were included in the study.Isolates that showed a resistant zone ( ≤ 19 mm ) to imipenem were screened by means of combined disc test (CDT), double disc synergy test (DDST) and E test (imipenem/imipenem+EDTA E strips, Biomeriuex). Multiplex PCR was done to confirm the presence of MBLgenes.

RESULTS : The study showed 49 isolates resistant to imipenem, of which 12 ( 24.48% ) were positive for MBL production by both combined and double disc methods; 37 ( 75.52% ) showed positivity by combined disc only and 12 ( 24.48% )isolates by double disc method only.Twelve isolates showed a MIC of ≥4µg/mLby E test .PCR detected genes in 11 isolates(22.4%) only.

CONCLUSION : Since phenotypic methods give variable results, it is not advisable to employ a single screening criterion for carbapenemase detection.Phenotypic methods though specific, do not differentiate between chromosomal and plasmid encoded genes and hence genotypic characterization ( PCR ) should be considered.

Keywords: Phenotypic methods, genotypic methods, Imipenem, Enterobacteriaceae