Exudative epidermitis in pigs caused by toxigenic Staphylococcus chromogenes

Area of Science:

• Veterinary Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Staphylococcus chromogenes is a common skin flora in pigs, cattle, and poultry.
• It is closely related to Staphylococcus hyicus, the known cause of exudative epidermitis (EE) in pigs.
• S. chromogenes has historically been regarded as non-pathogenic to swine.

Purpose of the Study:

• To investigate the pathogenic potential of Staphylococcus chromogenes in pigs.
• To identify and characterize exfoliative toxins produced by S. chromogenes.
• To determine if S. chromogenes can induce exudative epidermitis in experimentally inoculated pigs.

Main Methods:

• Multiplex PCR was used to detect exfoliative toxins specific to S. hyicus.
• Immunoblot analysis and antibody characterization were performed on the exfoliative toxin.
• Gene sequencing of the exfoliative toxin B (exhB) gene was conducted.
• Experimental inoculation of pigs with S. chromogenes strain VA654 followed by clinical and histopathological assessment.

Main Results:

• A strain of S. chromogenes (VA654) was identified producing exfoliative toxin type B (ExhB).
• The toxin showed cross-reactivity with antibodies against S. hyicus ExhB and had an apparent molecular weight of 30 kDa.
• Sequencing revealed minor differences in the exhB gene and deduced amino acid sequence compared to S. hyicus.
• Experimentally inoculated pigs developed generalized exudative epidermitis, with S. chromogenes identified as the causative agent.

Conclusions:

• Staphylococcus chromogenes can act as a causative agent of exudative epidermitis in pigs.
• The production of exfoliative toxin B by S. chromogenes is a key factor in its pathogenicity.
• This finding challenges the previous understanding of S. chromogenes as a non-pathogenic commensal in swine.