Identification of intermediately virulent Rhodococcus equi isolates from pigs

Area of Science:

• Veterinary Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Rhodococcus equi exhibits varying virulence, with distinct antigens associated with different pathogenicity levels in humans.
• While virulent R. equi (15-17 kDa antigens) are common in horses, the origin of intermediately virulent R. equi (20-kDa antigen) remains unclear.
• R. equi has been isolated from pig lymph nodes, prompting investigation into their role as a potential reservoir.

Purpose of the Study:

• To investigate the presence and characteristics of R. equi isolates from pig lymph nodes.
• To determine if pig R. equi isolates possess the 20-kDa antigen associated with intermediate virulence.
• To explore the association between plasmids, antigen expression, and pathogenicity in R. equi pig isolates.

Main Methods:

• Analysis of R. equi isolates from pig submaxillary lymph nodes.
• Immunoblotting using monoclonal antibodies against R. equi virulence-associated antigens.
• Plasmid profiling of R. equi isolates to assess genetic relatedness and virulence factors.

Main Results:

• The 20-kDa antigen was detected in nearly all R. equi isolates from pig lymph nodes.
• These pig isolates demonstrated intermediate virulence in mouse models.
• The 20-kDa antigen expression and mouse pathogenicity were strongly linked to five large plasmids (70-95 kb).

Conclusions:

• R. equi possessing the 20-kDa antigen are present in pig submaxillary lymph nodes.
• Pigs and their environment are suggested as a potential source for R. equi infections in humans.
• The study highlights the role of specific plasmids in the virulence of R. equi.