Investigating the Zoonotic Potential of Avian Pathogenic E. coli Isolates

Abstract

Escherichia coli, a facultative anaerobe is a gram-negative bacteria which normally inhabits the gut microflora. E. coli is very diverse in nature and mainly act as commensal bacteria that do not cause disease, but these bacteria can become pathogenic after acquiring virulence genes by horizontal gene transfer. Pathogenic E. coli can be of two types that are extraintestinal pathogenic Escherichia coli (ExPEC) or non-extraintestinal pathogenic Escherichia coli (ExPEC). Extra intestinal pathogenic E. coli cause disease outside the intestine. ExPEC are very diverse in nature and cause different types of infection in humans, dairy, and poultry for instance UTI, Colibacillosis and Mastitis respectively. E. coli strains have a zoonotic risk because some of the ExPEC isolates from liver of colibacillosis infected chicken have similarities with human ExPEC, that is they have several virulence and antimicrobial resistance genes in common. Humans may acquire these genes through a variety of interactions, including as personal contact with infected birds or through the food chain. However, nothing is known about the precise rate at which handling or consumption of ExPEC-contaminated food leads to intestinal colonisation and, eventually, extraintestinal infection from a poultry source. Examining the zoonotic potential of ExPEC isolates bearing the sub pathotype Avian pathogenic E. coli, or APEC, is the goal of the research that has been done. The evaluation of avian pathogenic E. coli isolates that cause colibacillosis in poultry, as well as the possibility that E. coli strains extracted from the liver of infected chickens can induce disease in chick models of avian colibacillosis and two mouse models of ExPEC related infections, such as human sepsis and urinary tract infections, are the main foci of this research. Through whole genome sequencing (WGS), 139 E. coli from liver source were categorized into ExPEC and non-ExPEC strains through screening for virulence associated genes. Based on this screening 54 out of 139 isolates were designated a ExPEC. Out of these 54, most of them belonged to APEC (45%). Among these isolates, the prevalent Sequence types were ST-131, ST-155, and ST-69. ST-69 is concerned with zoonotic infections and ST-155 is concerned with bloodstream infections. O131 and O2 were the prevalent serotypes. The bulk of the isolates from ExPEC belonged to phylogroups B1, D, and B2. Phylogroups B2 and D are very common phylogroups where zoonotic infections are concerned. The identified strains underwent screening to determine if they carried any common VAGS (virulence associated genes) or antimicrobial resistance genes, which can spread horizontally to other bacteria and eventually to humans. Almost 99% of the ExPEC isolates contained virulence associated genes that were associated with causing zoonotic infections. ExPEC isolates from avian source resembled human ExPEC isolates causing illnesses in humans and chicken through experimental animal infection models. ExPEC isolates from liver sources were able to cause colibacillosis in chicken and showed intermediate to high pathogenicity. ExPEC isolates also caused UTI infection and lethal sepsis in mice models. 2 of the ExPEC isolates that caused colibacillosis in chick model, caused lethal sepsis in mice and enormous bacterial counts in mice. Both of these strains belonged to phylogroup D and ST-69 which were proven to have a zoonotic lineage. These findings suggest that E. coli isolates from liver source harbor virulence genes that can be transferred to humans and can pose a severe threat to human health.