Class 1 and class 2 integrons in avian pathogenic Escherichia coli from poultry in Italy

The aim of this study was to investigate the occurrence of class 1 and 2 integrons in avian pathogenic Escherichia coli (APEC) from poultry in northern Italy. Strains were tested for phenotypic resistance to aminoglycosides and sulphonamides, and the association between the presence of integrons and the resistance to these antimicrobials was evaluated. A total of 299 isolates (158 from turkeys, 110 from broilers, and 31 from layer hens) were collected from 200 industrial farms. Antimicrobial susceptibility test by the disk diffusion method was performed in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines. All strains were screened for the presence of class 1 and 2 integrons by PCR and sequencing. About 55% of APEC contained integrons (class 1, 49.8%; class 2, 10.4%). Different variants of the aadA (5 variants) and the dfrA (4 variants) genes, encoding for streptomycin and trimethoprim resistance respectively, were detected in integron-positive isolates. Less common gene cassettes, such as sat, estX, and orfF, were also identified. Fifteen and 4 gene cassette arrays were found among class 1 and 2 integrons, respectively. High levels of resistance were observed for triple sulphonamides (79.3%), streptomycin (67.2%), and sulfamethoxazole combined with trimethoprim (62.2%), whereas resistance against gentamycin (16.7%), kanamycin (14.7%), and apramycin 3.0%) was low. Integron positivity was significantly higher in isolates phenotypically resistant to aminoglycosides (63.6% vs. 37.8%, P < 0.001) and sulfonamides (64.1% vs. 21.1%, P < 0.001) than in susceptible ones. Integron-borne aminoglycoside and sulfonamide resistance in APEC represents a concern for the poultry industry in Italy, since they are among the most commonly used antimicrobials in poultry therapy.