Abstract
BackgroundThe frequency of transfer of genes encoding resistance to antimicrobial agents was determined by conjugation in ESBL-producing and/or fluoroquinolone or aminoglycoside resistant Enterobacteriaceae clinical isolates at a tertiary care center in Lebanon. In addition, the role of tra genes encoding transferases in mediating conjugation was assessed.MethodsConjugation experiments were done on 53 ESBL-producing and/or fluoroquinolone resistant E. coli and K. pneumoniae and ESBL-producing S. sonnei isolates. Antimicrobial susceptibility testing on parent and transconjugant isolates, and PCR amplifications on plasmid extracts of the resistance-encoding genes: blaCTX-M-15 with the ISEcp1 insertion sequence, the aac(6')-lb-cr and qnrS genes, as well as tra encoding transferases genes were done. Random amplified polymorphic DNA (RAPD) analysis was performed to demonstrate whether conjugative isolates are clonal and whether they are linked epidemiologically to a particular source.ResultsAntimicrobial susceptibility testing on transconjugants revealed that 26 out of 53 (49%) ESBL-producing Enterobacteriaceae were able to transfer antimicrobial resistance to the recipients. Transfer of high-level resistance to the transconjugants encoded by the blaCTX-M-15 gene downstream the ISEcp1 insertion sequence against 3rd generation cephalosporins, and of low-level resistance against ciprofloxacin, and variable levels of resistance against aminoglycosides encoded by aac(6')-lb-cr gene, were observed in transconjugants. tra encoding transferase genes were detected exclusively in conjugative isolates.ConclusionIn conclusion, the frequency of transfer of antimicrobial resistance in non clonal Enterobacteriaceae at the tertiary care center by conjugation was 49%. Conjugation occurred in isolates expressing the tra encoding transferase genes. Multiple conjugative strains harboring the plasmid encoded antimicrobial resistant genes were circulating in the medical center. Molecular epidemiology analysis showed that conjugative isolates are neither clonal nor linked to a particular site and transfer of antimicrobial resistance is by horizontal transfer of plasmids.
Highlights
The frequency of transfer of genes encoding resistance to antimicrobial agents was determined by conjugation in Extended-spectrum b-lactamases (ESBL)-producing and/or fluoroquinolone or aminoglycoside resistant Enterobacteriaceae clinical isolates at a tertiary care center in Lebanon
This plasmid was found to harbor in addition to the blaCTX-M-15 gene, the aminoglycoside modifying enzyme encoding gene, aac (6′)-lb-cr, which confers resistance to two unrelated antimicrobial agent classes, the aminoglycosides and the fluoroquinolones, by acetylating these drugs
In this study, we determined the frequency and mode of transfer of resistance to antimicrobial agents by conjugation, among a number of multi-drug resistant Enterobacteriaceae isolates. These are all ESBL producing and/ or fluoroquinolone and aminoglycoside resistant. Most of these isolates harbor the pC15-1a plasmid, that carries the blaCTX-M-15 gene in addition to the aminoglycoside modifying enzyme aac(6′)lb-cr gene which confers some resistance to the fluoroquinolone ciprofloxacin as demonstrated in a previous study [8]
Summary
The frequency of transfer of genes encoding resistance to antimicrobial agents was determined by conjugation in ESBL-producing and/or fluoroquinolone or aminoglycoside resistant Enterobacteriaceae clinical isolates at a tertiary care center in Lebanon. PC15-1a, one of the plasmids responsible for the spread of the blaCTX-M-15 gene, was found associated with the Canadian outbreak, and its complete sequence was reported by Boyd et al [4]. This plasmid was found to harbor in addition to the blaCTX-M-15 gene, the aminoglycoside modifying enzyme encoding gene, aac (6′)-lb-cr, which confers resistance to two unrelated antimicrobial agent classes, the aminoglycosides and the fluoroquinolones, by acetylating these drugs. In addition the role of plasmid mediated tra genes encoding transferase proteins was assessed
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