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

Abstract

1. E. coli is an opportunist pathogen of animals, including food-producing ones and humans. Chickens may be a notable source of pathogenic and antimicrobial resistant E. coli for transmission to humans.2. This study compared virulence-associated genes (VGs) and antimicrobial resistance (AMR) in avian pathogenic E. coli (APEC) and extraintestinal pathogenic E. coli (ExPEC) isolates from broiler chickens, specifically APEC isolates in liver samples (n = 78) and ExPEC or non-ExPEC isolates in litter samples (n = 34). Virulence was evaluated by PCR for feoB, hlyF, iroN, iss, iutA and ompT genes, while AMR was evaluated by using antimicrobials from seven classes and detecting bla_SHV, bla_TEM, bla_OXA, qnrB, stcM, mrc1, mrc2, sul1 and tetA 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 feoB (100%), followed by ompT (63%), iutA (60%), iss (58%) and hlyF (43%). Surprisingly, iroN, omp T and iutA 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 stcM and tetA, respectively. No isolate was positive for bla_SHV, bla_OXA, mrc1 or mrc2, 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 E. coli isolates, improving biosecurity practices in chicken flocks should be prioritised to eliminate transmission to humans through the food chain.

Keywords: APEC; E. coli; broiler; carbapenem; colistin; multidrug resistant; virulence.