Antibiotico-resistenza e integroni di classe 1 e 2 in ceppi di Escherichia coli isolati da specie avicole commerciali

A total of 355 E. coli were analyzed to determine the phenotypic and genotypic (i.e. class 1 and 2 integrons) antimicrobial resistance (AMR). Strains were tested by the disk diffusion method according to CLSI (2006) standard against 21 antimicrobial drugs belonging to 8 classes. Class 1 and class 2 integrons were detected by PCR as described by Lévesque et al. (1995) and White (2001), slightly modified. Gene cassettes content was characterized by DNA sequencing. Phenotypic AMR results were: 90.4% of isolates resistant to tetracycline, followed by 85.9% to ampicillin, 80.6% to doxycycline, 80.3% to triple sulphonamides, 74.4% to nalidixic acid, 67% to streptomycin, 63.9% to trimethoprim/sulfamethoxazole, 50.1% to cephalothin, 40.3% to chloramphenicol, 31% to enrofloxacin, 25.1% to amoxicillin/clavulanic acid, 24.5% to norfloxacin, 23.9% to ciprofloxacin, 16.9% to kanamycin, 16.1% to gentamicin, 15.2% to ceftiofur, 9% to cefotaxime, 5.1% to ceftazidime, 3.4% to apramycin, 2.8% to colistin, and 1.4% to florfenicol. Both class 1 and class 2 integrons were found: 36% of strains carried class 1 integrons, 9% class 2 integrons and 3.4% both classes. Gene cassettes were mainly aadA, sat, dfrA and their variants, alone or in combination; whereas orfF and estX genes were more rarely detected. These genes confer resistance to aminoglycosides (i.e. streptomycin, streptothricin, and spectinomycin) and trimethoprim. AMR and integrons seems to be common among E. coli from poultry. Integrons represent important contributors in the dissemination of AMR.