Incidence of Enterococcus faecalis and Escherichia coli coinfection in nonviable embryonated broiler chicken eggs

    

Hatchability rates in the US broiler industry have been declining since 2014. The average weekly hatchability rate in the US in 2023 has been approximately 80.7%, a decrease of more than 4% since 2014. Published studies of nonviable embryos in Canada indicated that Enterococcus faecalis and Escherichia coli are frequently recovered from nonviable embryos and that infection by one or both bacteria may be contributing to the declining hatchability rates observed. E. faecalis and E. coli are ubiquitous in the poultry production environment and both are thought to be normal commensals of the poultry gastrointestinal microbiota. Although both bacteria can become opportunistic poultry pathogens, they are frequently recovered in high abundance from the intestinal tract of normal, healthy birds within a day of hatching, resulting in uncertainties around their role in the declining hatchability rates. To better understand this issue and the potential role of co-infection of embryonated eggs with E. faecalis and E. coli on decreasing hatchability rates in the US, we conducted a survey of nonviable broiler eggs to determine the prevalence of these bacteria in the samples. A total of 405 hatch residue samples were collected from eggs that had evidence of early embryonic mortality from 6 different hatcheries. Samples were collected by opening eggs aseptically and swabbing the yolk area, followed by standard microbiological methods to determine the presence of E. faecalis and E. coli. The prevalence of each bacteria recovered alone was compared against the prevalence of co-infection using one-way ANOVA. The prevalence of E. faecalis alone was 54 (13%), which was similar to the prevalence of E. coli alone at 53 (13%) (p> 0.5). However, co-infection with both bacteria was significantly more prevalent than either bacterium alone (p< 0.0001), with 174 samples (43%) positive for both bacteria. The remaining 124 samples (31%) were negative for both bacterial species. These results suggest that E. faecalis and E. coli may contribute to the decline in hatchability rates and that co-infection with E. faecalis and E. coli may enhance virulence of each bacterium leading to early embryonic mortality.

Key Words: Enterococcus faecalis, E. coli, Hatchability.