Pathogenic Enterococcus cecorum (EC) continues to plague the broiler industry, causing mortality from pericarditis and sepsis early in the growing period and lameness and paralysis late in the growing period.
As gut colonization is a necessary first step in EC infection, it is an attractive target for intervention. If EC can be excluded from the gut, systemic EC infection could be greatly diminished.
Research at North Carolina State University led by Mitsu Suyemoto tested the ability of recently generated, avirulent deletion mutants and commensal EC strains to disrupt gut colonization by pathogenic EC.
The project had two objectives:
1) Test the efficacy of avirulent EC deletion mutants and commensal EC strains as probiotics to competitively inhibit the early colonization of the broiler gut with pathogenic EC; and
2) Test the safety and efficacy of the EC deletion mutants as potential modified-live in ovo vaccines to protect against pathogenic EC.
Significant decrease in sepsis prevalence
Using the EC commensal strains as an orally delivered probiotic, researchers found a significant decrease in the sepsis prevalence in broilers at 2 weeks post challenge with pathogenic EC. However, this difference did not persist for the 5-week duration of the study.
The use of attenuated deletion mutants as probiotics did not disrupt long-term colonization of the gut by pathogenic EC, as no decrease in sepsis prevalence was seen at week 5 among treatment groups.
To mimic a natural infection more closely, researchers developed a new challenge protocol by decreasing the challenge dose 100-fold and only challenging a small number of birds per pen.
These changes were made to expand the sensitivity of the challenge model in detecting the efficacy of interventions designed to decrease pathogenic EC morbidity and mortality.
When tested as in ovo vaccines, neither the commensals nor the deletion mutants were effective in decreasing sepsis in the early life period, with no decrease in sepsis found among the treatment groups.
Safety concerns raised
In addition, safety concerns were raised with the use of the deletion mutants with one reverting to a virulent phenotype even though it was repeatedly shown to be completely avirulent in both the embryo lethality assay and bird challenge model.
This study found that oral inoculation of newly hatched chicks with commensal EC significantly decreased the sepsis prevalence at 2 weeks post challenge. Further investigation is needed to see if this effect could be extended for longer in the grow-out period, possibly through continuous feeding or water delivery.
Changes to EC challenge models should be considered in future work and may enable the discovery of successful interventions to decrease the morbidity and mortality of pathogenic EC infection. Additionally, caution should be used when testing even attenuated deletion mutants of EC as modified-live vaccines as reversion to virulence is possible.
The research was made possible in part by an endowing Foundation gift from Wayne-Sanderson Farms and proceeds from the International Poultry Expo, part of the International Production & Processing Expo (IPPE). The research is part of the USPOULTRY’s comprehensive research program encompassing all phases of poultry and egg production and processing.
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