Resumen

Background: Emergence of extended-spectrum β-lactamases (ESBLs) in Shigella species imparting resistance to third-generation cephalosporins is a growing concern worldwide. The aim of this study is to molecularly characterize the newly emerging beta-lactam resistant Shigella sonnei, specifically ESBLs in Lebanon, and compare them to beta-lactam sensitive isolates. Methodology: We compared five beta-lactam-resistant S. sonnei isolates to six isolates susceptible to beta-lactams. Presence of ESBLs was established by the combination disk method. PCR amplification and sequence analysis of the beta-lactamase-encoding genes, along with other antimicrobial resistance genes, were performed. The localization of beta-lactamase genes was established by conjugation experiments. Beta-lactamase gene transcription levels were determined by real-time RT-PCR. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE). Results: Four of five beta-lactam resistant isolates were extended spectrum beta-lactamase producers. These harbored the bla-_CTX-M-15 gene borne on a 70 Kb plasmid and class 2 integron genes on their chromosomes. The bla-_CTX-M-15 gene was flanked by an insertion element ISEcp1. A chromosomal bla-_TEM-1 gene was detected in one beta-lactam resistant Shigella isolate and two of the ESBL producing isolates. The bla-_CTX-M-15 gene transcription levels were increased in EBSL isolates exposed to subinhibitory concentrations of ceftazidime. PFGE analysis revealed that the four bla-_CTX-M-15 positive isolates were nonclonal but two of them shared genotypes with -lactam susceptible isolates. Conclusion: Dissemination of broad-spectrum beta-lactam resistance in Shigella sonnei is mediated by bla-_CTX-M-15 through horizontal plasmid transfer rather than by clonal spread of the resistant isolates. Expression of this gene is further induced in the presence of ceftazidime.

Palabras clave: Shigella sonnei extended spectrum beta-lactamase CTX-M-15 pulsed field gel electrophoresis gene expression.

2009-12-08   |   1,056 visitas   |   Evalua este artículo 0 valoraciones

Vol. 3 Núm.4. Abril 2009 Pags. 300-305. J Infect Developing Countries 2009; 3(4)