In vitro Evaluation of Candidate Bacillus Strains Against erysipelothrix rhusiopathiae from Erysipelas Outbreaks in Layer Flocks

Erysipelas is a zoonotic disease, causing acute infections in swine, poultry, and a wide variety of animals, including humans. In layers, erysipelas is considered an emerging disease characterized by hepatomegaly, splenomegaly, septicemia, and acute death. It affects flocks between 43 and 73 wk old and can result in 50% overall mortality. Layer hens possibly affected by an erysipelas outbreak were sampled in this study. Organs at necropsy showed the typical erysipelas lesions; the presence of <i>Erysipelothrix rhusiopathiae</i> was confirmed by selective plating and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The antimicrobial effect of a set of 20 proprietary <i>Bacillus</i> direct-fed microbials (DFM), individual strains and in combinations, was analyzed against confirmed <i>E. rhusiopathiae</i> isolates, by agar-well diffusion assay. Nine of the <i>Bacillus</i> strains screened in this study were found effective at inhibiting the growth of all four <i>E. rhusiopathiae</i> isolates from erysipelas cases. The findings of this study highlight the potential of using the <i>Bacillus</i> DFMs <i>in vivo</i> to evaluate their efficacy as biocontrol alternatives to reduce the growth <i>E. rhusiopathiae</i> in poultry production.