Antimicrobial susceptibility testing in predicting the presence of carbapenemase genes in Enterobacteriaceae in South Africa.

Olga Perovic,Ashika Singh-Moodley

doi:10.1186/s12879-016-1858-7

Olga Perovic, Ashika Singh-Moodley

Open Access

https://doi.org/10.1186/s12879-016-1858-7

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Abstract

BackgroundCarbapenem-resistant Enterobacteriaceae (CRE) is a concern in South Africa and worldwide. It is therefore important that these organisms be accurately identified for infection prevention control purposes.MethodIn this study 1193 suspected CREs from 46 laboratories from seven provinces in South Africa were assessed to confirm the prevalence of carbapenemase genes from our referral diagnostic isolates for the period 2012 to 2015. We compared the antimicrobial susceptibility testing method used in the reference laboratory to the polymerase chain reaction (PCR) which is used as the gold standard. Organism identification and antimicrobial susceptibility testing were performed using automated systems and DNA was extracted using a crude boiling method. The presence of carbapenemase-producing genes (bla NDM, bla KPC, bla OXA-48&variants, bla GES, bla IMP and bla VIM) was screened for using a multiplex real-time PCR.ResultsSixty-eight percent (n = 812) of the isolates harboured a carbapenemase-producing gene; the three most common genes included: bla NDM, bla OXA-48&variants and bla VIM. Majority of the carbapenemase producing Enterobacteriaceae (CPE) isolates were Klebsiella species (71 %). The Microscan® Walkaway system used for the screening of carbapenemase production was 98 % sensitive with a minimal inhibitory concentration (MIC) breakpoint of less than 0.5 as susceptible for ertapenem and a low specificity (13 %).ConclusionFrom this study we can conclude that carbapenemase-producing Enterobacteriaceae is increasing in South Africa and the use of phenotypic methods for detection of CPEs showed good sensitivity but lacked specificity.

Highlights

Carbapenem-resistant Enterobacteriaceae (CRE) is a concern in South Africa and worldwide
From this study we can conclude that carbapenemase-producing Enterobacteriaceae is increasing in South Africa and the use of phenotypic methods for detection of Carbapenemase-producing Enterobacteriaceae (CPE) showed good sensitivity but lacked specificity
We evaluated one of the phenotypic methods routinely used for antimicrobial susceptibility testing (AST) to determine its efficacy and accuracy and report on its ability to screen for CREs based on confirmed CPE genes received at the reference laboratory

Summary

Introduction

Carbapenem-resistant Enterobacteriaceae (CRE) is a concern in South Africa and worldwide. Multidrug resistant organisms are a major public health concern [1, 2]. There is an increase in the global detection of antibiotic resistant Enterobacteriaceae strains with antibiotic resistance observed to beta-lactams, fluoroquinolones, aminoglycosides and polymixins [3]. Beta-lactam resistance mechanisms include outer membrane permeability changes, efflux pumps and enzymes that hydrolyse the antibiotic for example, the carbapenemases, including: the metallo-beta-lactamases (MBLs), NDM, IMP and VIM; the oxacillinases, OXA-48 and non-metallo-enzymes, Klebsiella pneumoniae carbapenemases (KPC) [3]. Carbapenemase-producing Enterobacteriaceae (CPE) are carbapenem-resistant Enterobacteriaceae (CRE) that are resistant to carbapenems due to carbapenemase production [7]. Carbapenemases are beta-lactamases [8] that hydrolyse almost all beta-lactams including the carbapenems [3, 9]. Carbapenemases were initially chromosomallymediated in a few specific species, majority are

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