Avian colibacillosis is an infection caused by a strain of E. coli called avian pathogenic E. coli (APEC). Specifically adapted to birds, it can cause septicemia, organ failure and death. The infection is estimated to cost the U.S. poultry industry millions of dollars a year in losses.

“The way we rear poultry can create a perfect storm of colibacillosis,” says Grayson Walker, a combined DVM and Ph.D. student in Dr. Luke Borst’s laboratory at NC State’s College of Veterinary Medicine and first author of the study. “If one egg in a hatchery is contaminated, it could spread to an entire farm.”

Walker and his colleagues observed six poultry flocks – three chicken flocks and three turkey flocks – for over a three-year period, taking post-mortem samples from birds suspected to have colibacillosis and culturing them to see which bacteria were present. They cultured both Enterococcus faecalis (EF) bacteria and APEC from many of the samples, and wanted to find out whether the presence of both bacteria increased mortality rates in birds. Enterococcus species are normally present in the gastrointestinal tracts of birds, but some strains – such as EF – have recently been associated with more serious infections in birds.

“Given the prevalence of co-isolated pathogens in post-mortem samples, we hypothesized that co-infections are more likely to result in death of the animal compared to single-species infections from which birds may be more likely to recover,” says Walker.

The researchers created an embryo infection model, in which embryos were exposed to just EF, just APEC, or both. The researchers found that co-infection with both APEC and EF resulted in a 95% mortality rate, which was three times higher than that caused by EF alone (32%) and substantially more than APEC alone (59%).

“This is a preliminary study,” says Walker. “Our next steps will involve looking more closely at synergies between these pathogens in colibacillosis. But we do know that all poultry are affected by this disease, it’s expensive for the industry, and Enterococcus could be playing a previously unknown role in its progression.”