JAC Advance Access originally published online on April 7, 2006
Journal of Antimicrobial Chemotherapy 2006 57(6):1210-1214; doi:10.1093/jac/dkl127
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Phenotypic and genotypic characterization of antimicrobial resistance in Escherichia coli O111 isolates
1 Federal Institute for Risk Assessment (BfR), Diedersdorfer Weg 1 D-12277 Berlin, Germany 2 Universidade Federal de São Paulo, Escola Paulista de Medicina CEP 04023-062, São Paulo, Brazil
Received 1 December 2005; returned 31 January 2006; revised 15 March 2006; accepted 16 March 2006
*Corresponding author. Tel: +49-30-8412-2057; Fax: +49-30-8412-2000; E-mail: b.guerra{at}bfr.bund.de
Objectives: The aim of this study was to generate baseline data on the prevalence and molecular basis of antimicrobial resistance in Escherichia coli O111 isolates.
Methods: A total of 105 epidemiologically unrelated E. coli O111 isolates from humans and cattle (isolated between 1983 and 2003) were tested for susceptibility to 17 antimicrobial agents by broth microdilution. Resistant isolates were screened by molecular methods for resistance genes, class 1 and 2 integrons and mutations in the quinolone-resistance determining regions.
Results: Resistance was found in 76% of the isolates, with a prevalence of 72% for multiresistance. The most prevalent resistances were to streptomycin, sulfamethoxazole and tetracycline (72–68%), followed by spectinomycin, ampicillin and kanamycin/neomycin (39–25%). For each antimicrobial agent, the predominant resistance genes were ampicillin, blaTEM (94%); chloramphenicol, catA1 (100%); gentamicin, aac(3)-IV and aac(3)-II (50% each); kanamycin, aphA1 (100%); streptomycin, aadA1- like (66%); sulfamethoxazole, sul1 (59%); tetracycline, tet(A) (86%); and trimethoprim, dfrA1-like (83%). Class 1 integrons were found in 41% of the isolates. They carried aadA1, dfrA1-aadA1 and dfrA15-aadA1. A class 2 integron (dfrA1-sat1-aadA1) was found in one isolate. Only three isolates (3%) were resistant to nalidixic acid (reduced susceptibility to ciprofloxacin), with a single mutation in the gyrA gene.
Conclusions: E. coli O111 strains exhibit a wide repertoire of genetic elements to sustain antimicrobial pressure. Two specific antimicrobial resistance pheno/genotypes, [STR-SPT]-SUL-TET/aadA1-sul1-tet(A) and STR-SUL-TET-AMP-[KAN-NEO]/strA/B-sul2-tet(A)-blaTEM-aphA1, are predominant.
Keywords: STEC , molecular epidemiology , resistance genes , resistance determinants , integrons
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