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Title: Absence of human innate immune evasion complex in LA-MRSA ST5 strains isolated from pigs, swine facilities, and humans with swine contact

item HAU, SAMANTHA - Iowa State University
item FRANA, IMOTHY - Iowa State University
item DAVIES, PETER - University Of Minnesota
item SUN, JISUN - University Of Minnesota
item Nicholson, Tracy

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2015
Publication Date: 11/2/2015
Citation: Hau, S., Frana, I., Davies, P.R., Sun, J., Nicholson, T.L. 2015. Absence of human innate immune evasion complex in LA-MRSA ST5 strains isolated from pigs, swine facilities, and humans with swine contact. 4th ASM-ESCMID Conference on Methicillin-resistant Staphylococci in Animals: Veterinary and Public Health Implications. Abstract No. 29.

Interpretive Summary:

Technical Abstract: Background: Since its first ties to swine, livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has raised public health concerns because livestock may be the largest reservoir of MRSA outside the hospital setting. In contrast to Europe and Asia, where the primary sequence type (ST) of swine associated LA-MRSA are ST398 and ST9 respectively, US strains are more diverse with ST5, ST398, and ST9 being isolated. The presence of ST5 MRSA in swine increases concern because, unlike ST398 and ST9, ST5 MRSA is among the most prevalent lineages causing human disease. A primary factor contributing to the clinical impact of ST5 MRSA is the capacity to acquire mobile genetic elements carrying virulence factors and resistance genes. Previous reports establishing the absence of most virulence genes in swine associated ST398 isolates and the lack of disease reports in humans occupationally exposed to swine carrying ST5 MRSA, suggests virulence factors contributing to human disease may also be uncommon in swine associated ST5 strains. Materials: ST5 isolates collected from swine, swine facilities, and humans with short- and long-term swine contact were PCR screened for the presence of human-specific virulence factors carried by beta-hemolysin converting bacteriophages including: staphylococcal complement inhibitor, chemotaxis inhibitory protein, staphylokinase, enterotoxin A, and enterotoxin P. PCR evaluation of the beta-hemolysin gene was used to determine if the gene was intact. Results: All LA-MRSA ST5 isolates screened lacked the virulence factors found in beta-hemolysin converting bacteriophages. An intact beta-hemolysin gene was also found in all isolates indicating the absence of beta-hemolysin converting bacteriophages in these isolates. Conclusion: The absence of beta-hemolysin-converting bacteriophages and their associated human specific virulence factors is consistent with the hypothesis that LA-MRSA strains that are adapted to swine have a reduced capacity to cause significant disease in immunocompetent humans.