Resumo

Introduction: Food-producing animals could serve as important reservoirs of ESBL-producing bacteria. Objective: This study evaluated the phenotype and genotype of bla_CTX-M-2 in Escherichia coli isolated from chickens. Material and methods: Two-hundred cloacal swabs were collected from broiler chickens in two poultry farms from Sao Paulo State, Brazil. Samples were selected in MacConkey agar with cefotaxime and ceftazidime (1µg/mL, each). E. coli isolates were identified and confirmed by the API 20E test (BioMérieux, France). ESBL-producers were investigated by double disk synergism using cefotaxime and ceftazidime plus amoxicillin/clavulanic acid. PCR and sequencing were performed to detect bla_CTX-M-2 genes. Genomic relationship was evaluated by pulsed-field gel electrophoresis (PFGE) after enzymatic digestion with XbaI enzyme and the isolates were considered from the same cluster when the genomic similarity was greater than to 85%. Replicons of the major plasmid incompatibility groups (Inc) among Enterobacteriaceae were investigated and characterized following the PCR-based replicon typing scheme. Localization of the bla_CTX-M-2 was investigated using PFGE after DNA digestion with S1 and I-Ceu-I enzymes, followed by the Southern blot and hybridization with the bla_CTX-M-2 probe, Inc plasmid probes and the E. coli 16S rRNA specific probe. Results and discussion: Nineteen ESBL-producing E. coli were detected, harboring the bla_CTX-M-2 gene. Six isolates from farm 1 were classified in four different clusters (A, B, C and D). On farm 2, 13 isolates were separated in two clusters (E and F). All 19 E. coli isolates presented the replicons F, B/O, K, I1 and FIB. There was no hybridization with Inc plasmid probes, however co-hybridization of bla_CTX-M-2 and E. coli 16S rRNA probes occurred and revealed the insertion of this resistance gene in the chromosome of the ESBL-producing isolates. The continuous use of cephalosporins on poultry farms may influence on the insertion of bla_CTX-M-2 into bacterial chromosome. This hypothesis is supported due to different pulsotypes found in two farms. CONCLUSION: This study characterized and identified rare insertion of bla_CTX-M-2 resistance gene into the bacterial chromosome.