Mohsen Kalantari - Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
Hassan Sharifiyazdi - Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
Keramat Asasi - Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran
Bahman Abdi-Hachesoo - Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran

The objective was to investigate the multidrug resistance and presence of class ۱ and ۲ integrons in ۳۰۰ Escherichia coli isolates obtained from ۲۰ broiler farms during three rearing periods (one-day-old chicks, thirty-day-old chickens, and one day before slaughter) in Fars, South Iran. Results showed that ۸۱.۰۰%, ۸۲.۰۰%, and ۸۵.۰۰% of isolates were multidrug-resistant on the first day, thirty-day-old chickens, and one day before slaughter, respectively. Multidrug-resistant E. coli isolates were further examined for the presence of class ۱ and ۲ integrons using PCR assay. The existence of class ۱ integron-integrase gene (intI۱) was confirmed in ۶۸.۴۰%, ۷۲.۷۰%, and ۶۰.۹۰% of multidrug-resistant isolates from stage ۱, stage ۲, and stage ۳ of the rearing period, respectively. The frequency of class ۲ integron-integrase gene (intI۲) during the first to the third stage of sampling was ۲.۶۰%, ۲۵.۵۰%, and ۳۰.۴۰%. Also, sequence analysis of the cassette arrays within class ۱ integron revealed the presence of the genes associated with resistance for trimethoprim (dfrA), streptomycin (aadA), erythromycin (ereA), and orfF genes. The results revealed that percentages of antimicrobial resistance in E. coli isolates were significantly higher in the middle and end stages of the rearing period. In conclusion, widespread dissemination of class ۱ integrons in all three stages and rising trends of class ۲ integrons existence in E. coli isolates during the rearing period of broiler chickens could exacerbate the spread of resistance factors among bacteria in the poultry industry. Future research is needed to clarify its implication for human health.

Broilers, Escherichia coli, Gene cassettes, Integrons, Multidrug resistance