Antimicrobial resistance and class 1 and 2 integrons among Escherichia coli isolates from poultry in Italy

A total of 329 E. coli were analyzed to determine the phenotypic and genotypic (i.e. class 1 and 2 integrons) antimicrobial resistance (AMR). Strains were collected between 2010 and 2012 in industrial poultry farms throughout Italy. One hundred and ten E. coli were from broilers, 188 from meat turkeys, and 57 from layer hens. Strains were tested by the disk diffusion method according to CLSI (2006) standard, against 21 antimicrobial drugs belonging to 8 classes: aminoglycosides (streptomycin, gentamicin, kanamycin, apramycin); cephalosporins (cephalothin, cefotaxime, ceftiofur, ceftazidime); quinolones (nalidixic acid, enrofloxacin, ciprofloxacin, norfloxacin); phenicols (chloramphenicol, florfenicol); penicillines (ampicillin, amoxicillin/clavulanic acid); tetracyclines (tetracycline, doxycycline); sulphonamides (triple sulphonamides, trimethoprim/sulfamethoxazole); polymyxins (colistin). Class 1 and class 2 integrons were detected by real-time PCR as described by Ekkapobyotin et al. (2008), slightly modified. Gene cassettes content was characterized by DNA sequencing. Phenotypic AMR results were: 91.05% of isolates resistant to tetracycline, followed by 86.63% to ampicillin, 82.41% to doxycycline, 80.49% to triple sulphonamides, 75.99% to nalidixic acid, 68.6% to streptomycin, 63.72% to trimethoprim/sulfamethoxazole, 51.98% to cephalothin, 39.94% to chloramphenicol, 35.52% to enrofloxacin, 27.05% to amoxicillin/clavulanic acid, 25.53% to norfloxacin, 25.23% to ciprofloxacin, 17.33% to kanamycin, 16.72% to gentamicin, 15.2% to ceftiofur, 9.73% to cefotaxime, 4.26% to ceftazidime, 3.34% to apramycin, 2.47% to colistin, and 1.52% to florfenicol. Three hundred and one strains showed multidrug resistance against 3 up to 7 antimicrobial classes, with 65 strains resistant to all antimicrobial classes except for polymyxins. Both class 1 and class 2 integrons were found: 38.91% of strains carried class 1 integrons, 9.42% class 2 integrons and 3.65% both classes. Gene cassettes content of class 1 integrons was: dfrA1-aadA1 (61 strains), aadA1 (37), estX (8), sat (5), dfrA12-orfF-aadA2 (4), dfrA12-aadA2 (3), dfrA7 (2), estX-aadA1 (2), dfrA17-aadA5 (1), aadA5 (1), aadA2 (1), sat2-aadA1 (1), dfrA12-orfF (1), aadA13 (1). Gene cassettes content of class 2 integrons was: drfA1-sat2-aadA1 (13 strains), dfrA1-aadA1 (10), sat2-aadA1 (8). These genes confer resistance to sulphonamides, aminoglycosides (i.e. streptomycin, streptothricin, and spectinomycin), and trimethoprim. AMR and integrons seems to be common among E. coli from poultry. Integrons may represent important contributors in the dissemination of AMR.