Embryo Lethality Assay for Evaluating Virulence of Isolates from Bacterial Chondronecrosis with Osteomyelitis in Broilers

Abstract

We used an embryo lethality assay (ELA) to assess virulence for different isolates from cases of bacterial chondronecrosis with osteomyelitis (BCO) in broilers. ELA has been used to measure virulence and lethal dosage of Enterococcus faecalis and Enterococcus cecorum. We hypothesized that ELA could substitute for more laborious and costly assessments of BCO isolate pathogenicity using live birds. We evaluated two different levels of bacteria injected into eggs from layer and commercial broiler embryos. Significant findings include a) Escherichia coli from neighboring farms operated by the same integrator had very different embryo lethality, b) isolate Staphylococcus agnetis 908 had low virulence in ELA, even though this isolate can induce more than 50% BCO lameness, c) Enterococcus cecorum 1415 also had low pathogenicity; even though it was recovered from severe bilateral tibial dyschondroplasia, d) human and chicken isolates of S. aureus had significant pathogenicity, e) virulence for some isolates was highly variable possibly corresponding with quality of the embryos/fertile eggs used, and f) ELA pathogenicity was much lower for our BCO isolates than previous reports which may reflect maternal environment. Overall, ELA virulence and BCO virulence are not always concordant indicating that that ELA may not be an effective measure for assessing virulence with respect to BCO.

Different virulence levels of Enterococcus cecorum strains in experimentally infected meat-type chickens

“…Nevertheless, it has been recently discussed whether embryo lethality assays are reliable tools to determine EC pathogenicity. In a recent study, an EC strain isolated from severe bone lesions had low pathogenicity in an embryo lethality assay, leading to the conclusion that those assays are not the most representative measures to determine EC pathogenicity [28]. Our findings strengthen this hypothesis.…”

“…Embryo lethality assays have also been used to characterize the virulence of EC strains. Extraintestinal EC isolates seem to cause higher embryo lethality rates and are therefore thought to be more virulent than intestinal strains [21,[26][27][28]. Nonetheless, until now, there is no experimental evidence that some strains are more virulent than others in broiler chicks in the first weeks of life.…”

Lameness caused by Staphylococcus aureus in poultry: A review

“…Their results showed that the causative agents of lameness due to bacterial chondronecrosis and osteomyelitis lesions can significantly differ in specific farms. Moreover, genotyping demonstrated that the genomes of S. aureus in this study were significantly related to isolates obtained from European chickens (25).…”

“…In another study, Ekesi (2020) analyzed the genomes of bacteria isolated from the lameness outbreak in boiler farms in Arkansas, USA (25). Simon and colleagues isolated several distinct bacterial species from chondronecrosis and osteomyelitis lesions.…”