RESEARCH ARTICLE Open Access Molecular characterization of multidrug-resistant extended-spectrum β-lactamase-producing Enterobacteriaceae

Background: We investigated the molecular characteristics of multidrug-resistant, extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae isolated in community settings and in hospitals in Antananarivo, Madagascar. Results: Forty-nine E. coli, K. pneumoniae, K. oxytoca and E. cloacae ESBL-producing isolates were studied. In antimicrobial susceptibility analyses, many of the isolates exhibited resistance to aminoglycosides, fluoroquinolones and trimethoprim-sulfamethoxazole. Gene amplification analysis and sequencing revealed that 75.5 % (n=37) of the isolates harbored blaCTX-M-15 and 38.7 % (n=19) harbored blaSHV-12. The non-ESBLs resistance genes detected were blaTEM-1, blaOXA-1, aac(6 0)-Ib, aac(60)-Ib-cr, tetA, sul-1, sul-2, qnrA, qnrB and catB-3. We found dfrA and aadA gene cassettes in the class 1 integron variable regions of the isolates, and the combination of dfrA17-aadA5 to be the most prevalent. All blaCTX-M-15 positive isolates also contained the ISEcp1 insertion element. Conjugation and transformation experiments indicated that 70.3 % of the antibiotic resistance genes resided on plasmids. Through a PCR based replicon typing method, plasmids carrying the blaSHV-12 or blaCTX-M-15 genes were assigned to either the IncFII replicon type or, rarely, to the HI2 replicon type. All isolates were subtyped by the rep-PCR and ERIC-PCR methods. Phylogenetic grouping and virulence genotyping of the E. coli isolates revealed that most of them belonged to grou