Comparative analysis of USA300 virulence determinants in a rabbit model of skin and soft tissue infection

Abstract

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are frequently associated with strains harboring genes encoding Panton-Valentine leukocidin (PVL). The role of PVL in the success of the epidemic CA-MRSA strain USA300 remains unknown. Here we developed a skin and soft tissue infection model in rabbits to test the hypothesis that PVL contributes to USA300 pathogenesis and compare it with well-established virulence determinants: alpha-hemolysin (Hla), phenol-soluble modulin-alpha peptides (PSMα), and accessory gene regulator (Agr). The data indicate that Hla, PSMα, and Agr contribute to the pathogenesis of USA300 skin infections in rabbits, whereas a role for PVL could not be detected.

Figure 1.

Pathology of rabbit skin abscesses caused by USA300 (LAC). USA300 abscesses 2 days (A–C), 6 days (D–F), or 14 days (G–I) post infection as indicated. A, D, and G, gross skin pathology. Note that hair was removed prior to inoculation. B, E, and H, representative histopathological sections of a typical rabbit skin abscess at 2, 6, and 14 days post infection as indicated. Original magnification is ×20. C, F, and I, increased magnification of an area of each abscess center at 2, 6, and 14 days post infection. Original magnification is ×1000.

Figure 2.

Contribution of selected USA300 molecules to the formation of rabbit abscesses. A, Average abscess volume for rabbits infected with USA300 (LAC) wild-type or isogenic gene deletion strains as indicated. Results are the mean of 10 abscesses from 5 animals (2 per rabbit). B, USA300 CFUs recovered from rabbit abscesses on day 6 post infection. Each symbol represents data from 1 abscess and the line indicates the mean. C, average abscess volume for rabbits used in B. Data are from rabbit abscess experiments distinct from those shown in A. For A–C, *P < .05 vs LAC wild-type using a 1-way analysis of variation (ANOVA) and Dunnett test to correct for multiple comparisons. Asterisks in A are matched by color to the appropriate mutant strain. CFUs, colony-forming units.