Molecular Characterization and Antibiotic Resistance of Avian Pathogenic Escherichia coli (APEC) Isolates from Broiler Chickens in Algeria

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis, a disease responsible for high morbidity and mortality in commercial poultry flocks, leading to devastating economic losses to the poultry industry worldwide. APEC may also act as a source of virulence and antibiotic resistance genes that can be transferred to other Escherichia coli pathotypes. Therefore, this study aimed to determine the serotypes, phylogenetic background, virulence genes, and antibiotic resistance profiles of APEC in Algeria. A total of 98 APEC strains were isolated from chicken samples with characteristic colibacillosis signs between 2019 and 2020. O-serotyping identified O157 (20.41%) and O78 (11.22%) as the predominant serotypes. The isolates were classified into groups B1 (43.87%), C (29.59%), A (12.24%), E (7.14%), F (5.10%), and B2 (2.04%). Virulence gene analysis revealed that among the 31 genes investigated, a high occurrence of mat, crlA (100% each), yijP (98.98%), fimC, ibeB, ompA (97.96% each), iucD (89.80%), iroN (81.63%), iss (80.61%), and eae (79.59%) was observed. The highest resistance rates were found for ampicillin (97.96%), amoxicillin–clavulanic acid (96.94%), nalidixic acid (94.90%), tetracycline (90.82%), and ciprofloxacin (79.59%). Additionally, 92.86% of APEC isolates were resistant to three or more antibiotics, reflecting extensive antimicrobial use in Algerian poultry farms and highlighting a major challenge for both animal health management and potential zoonotic transmission. Our data provide valuable insights into the characteristics of the APEC populations in broiler chickens in Algeria. This may assist in understanding APEC pathogenesis and in developing effective control strategies.