Fecal E. coli from Chickens May Pose Health Risks to Poultry and Humans

A study recently published in PLoS ONE reported the virulence of extraintestinal pathogenic Escherichia coli (ExPEC) from healthy chickens.

“This study,” the investigators wrote, “provides the strongest evidence to date that chicken feces could be a source of virulent ExPEC that are able to infect humans and poultry.”

E. coli populates the lower intestinal tract of chickens. Although primarily commensal, E. coli has pathogenic strains that cause intestinal and extraintestinal disease.

Notably, ExPEC strains contain virulence genes that enable extraintestinal disease. These strains are classified according to infection site:

• Uropathogenic E. coli (UPEC)
• Avian pathogenic E. coli (APEC)
• Sepsis-associated E. coli (SEPEC)
• Neonatal meningitis E. coli (NMEC)

ExPEC transmission between chickens increases the risk of contamination onto poultry products. This contamination, along with contamination at slaughter (eg, digestive tract rupture during processing) and cross-contamination during food preparation, increases the likelihood of ExPEC transmission to humans. To date, the frequency of ExPEC transmission to humans and subsequent disease remains unknown.

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A better understanding of health risks posed by fecal E. coli from chickens is needed to develop measures to prevent infection and food contamination, wrote the investigators.

Study Design

Investigators collected fresh fecal samples from farm-housed healthy commercial chickens in Quebec, Canada. From these samples, 304 fecal E. coli isolates were obtained. Via polymerase chain reaction (PCR), the isolates were tested for the presence of several virulence genes associated with extraintestinal E. coli infection.

PCR-positive isolates (175/304) underwent further PCR screening to determine ExPEC status (ExPEC vs non-ExPEC). Of these 175 isolates, 40 qualified as ExPEC; ExPEC isolates were primarily APEC and UPEC, with no NMEC.

Following PCR screening, investigators selected 40 ExPEC and 37 non-ExPEC isolates for additional testing.

Results

Phylogenetics

Phylogenetic analysis evaluates evolutionary relationships. E. coli has 4 phylogroups (A, B1, B2, and D). Previous studies have reported differential phylogroup distribution according to ExPEC status. In this study, ExPEC isolates were more prevalent than non-ExPEC isolates in phylogroups A and D; the opposite was true for phylogroup B1. Phylogroup B2 contained similar percentages of both isolate types.

Phenotypic Screening

The investigators screened for several virulence phenotypes. Of note, biofilm production was present in all ExPEC isolates. Also, compared with non-ExPEC isolates, ExPEC isolates had significantly greater siderophore production; siderophores are iron-chelating agents that help bacteria survive and thrive in harsh environments. Whether biofilm and siderophore production allow ExPEC to adhere to and survive on poultry products warrants further study, the investigators noted.

Virulence in Animals

The investigators used animal models of avian colibacillosis, sepsis, urinary tract infection (UTI), and meningitis. Animals were inoculated with the fecal isolates or control E. coli strains; control strains were positive or negative for the evaluated disease.

Several pertinent findings were observed:

• Avian colibacillosis model—ExPEC isolates were detected in multiple internal organs of healthy chickens, suggesting E. coli transmission between chickens in poultry farms
• Mouse sepsis model—ExPEC and non-ExPEC isolates produced significant morbidity and mortality
• Mouse ascending UTI model—ExPEC and non-ExPEC isolates had markedly high bacterial loads in the bladder, kidney, and liver
• Rat meningitis model—One ExPEC isolate had a high bacterial load in the blood and cerebrospinal fluid

Because there were no NMEC isolates, investigators used isolates positive for 1 of 2 meningitis markers in the rat meningitis model.

Bringing It Together

With their study, the investigators described the in vitro and in vivo virulence of fecal ExPEC isolates from healthy commercial chickens, highlighting the serious health risk of this bacterium. Additional studies, they noted, are needed to further understand the mechanisms of ExPEC virulence and the frequency of ExPEC transmission to humans.

Dr. JoAnna Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.