Abstract:
Improper monitoring of antibiotic usage has lead to the development of
antimicrobial resistance among uropathogenic Escherichia coli (UPEC). The rapid
dissemination of antibiotic-resistance is mediated by gene transfer mechanisms
involving mobile genetic elements including the recendy characterized gene
cassettes in integrons. Integrons are conserved DNA sequences associated with
multi-drug resistance. The aim of this study was to generate data on the
prevalence and molecular basis of antimicrobial resistance in UPEC in
Lebanon. The phenotypic resistance profiles of 9 currendy used antimicrobial
agents were determined using the agar diffusion test on a total 100 UPEC
isolates. Results obtained revealed that 60% of the isolates were resistant to
ampicillin, 55% to trimethoprim/ sulfamethoxazole, 53% to streptomycin and
only 5% to netilmicin. PCR assay was used to detect the presence of the class 1
integron variable region (VR) containing the gene cassettes. All VR negative
isolates showed more susceptibility towards the used antimicrobial agents
compared to the VR positive isolates. The VR positive isolates showed highest
resistance to aminoglycosides and trimethoprim/sulfamethoxazole (96.7%). VR negative islolates were mainly resistant to ampicillin (48.6%), aminoglycosides
(41%), and tetracycline (40%). The VR amplicons were then characterized by
direct partial sequencing and restriction digestion with AluI, and accordingly, 30% of the isolates were found to be positive for the Class 1 integron VR, with
a size ranging from 0.7 to 2.2 Kbp. VR positive isolates carried the genes 4frA7,
4frAI7-aadA5, 4frAl-aadA1, 4frAI2-orf5-aadA2 and blaoXA
_
30-aadAl. The
predominant resistance genes were 4frA 17 and aadA5 (47% of the isolates) for
trimethoprim/ sulfamethoxazole and streptomycin, respectively. The presence
of a gene cassette was correlated with high resistance to the corresponding
antibiotic, with 85.7% of the isolates harboring the aadA gene being resistant to
streptomycin. Five different restriction patterns were detected; all isolates with
the same class 1 integron VR amplicon size had the same restriction pattern.
Characterization of class I integrons from UPEC isolates by direct sequencing
revealed that those isolates exhibit a wide repertoire of genetic elements to
sustain antimicrobial pressure. This study provided basal information for future
pursuit and comparison especially with respect to epidemiologic distribution,
antimicrobial resistance and evolution of these important pathogens.
