Comparison of pathogenicity factors of avian pathogenic and extraintestinal pathogenic isolates originating from broiler chickens.

1. is an opportunist pathogen of animals, including food-producing ones and humans. Chickens may be a notable source of pathogenic and antimicrobial resistant for transmission to humans.2. This study compared virulence-associated genes (VGs) and antimicrobial resistance (AMR) in avian pathogenic (APEC) and extraintestinal pathogenic E. coli (ExPEC) isolates from broiler chickens, specifically APEC isolates in liver samples ( = 78) and ExPEC or non-ExPEC isolates in litter samples ( = 34). Virulence was evaluated by PCR for and genes, while AMR was evaluated by using antimicrobials from seven classes and detecting and genes.3. The APEC isolates were found in 100% of livers, while ExPEC and non-ExPEC isolates were found in 44% and 56% of the litter samples. The predominant VG was (100%), followed by (63%), (60%), (58%) and (43%). Surprisingly, and had higher prevalences in APEC isolates (85%, 96% and 96%, respectively) than in ExPEC isolates (73%, 87% and 73%, respectively) and non-ExPEC isolates (0% for all). The presence of all VG in 33% of isolates indicated high pathogenicity.4. The isolates were phenotypically resistant to ampicillin (93%), ceftazidime (72%) and nalidixic acid (82%). All APEC and ExPEC isolates (100%) were multidrug resistant (MDR), while 63% of non-ExPEC isolates were MDR. Genotypic AMR testing revealed that 53% and 52% of all isolates had and , respectively. No isolate was positive for or , which suggested the benefits of colistin for treating carbapenem-resistant enteric pathogens, due to the high resistance detected to meropenem (47%).5. Given the potential pathogenicity of isolates, improving biosecurity practices in chicken flocks should be prioritised to eliminate transmission to humans through the food chain.