Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Tight regulation of Staphylococcus aureus proteases is essential for in vivo pathogenesis (#161)

Allister J. Loughran 1 , Daniel G. Meeker 1 , Karen E. Beenken 1 , Mark S. Smeltzer 1
  1. Microbiology and Immunology, University of Arkansas for Med. Sci., Little Rock, AR, United States
We previously demonstrated that mutation of the staphylococcal accessory regulator (sarA) reduces the capacity of Staphylococcus aureus to cause hematogenous osteomyelitis and that this is due to the increased production of extracellular proteases. To determine whether this is also true in acute, post-traumatic osteomyelitis, we used a murine model in which bacteria were deposited directly into a bone defect. These experiments were done with the S. aureus clinical isolate LAC, its isogenic sarA mutant, and an isogenic sarA mutant unable to produce extracellular proteases. The results confirmed that mutation of sarA limits the bone destruction that characterizes the acute phase of infection and that this is due to the increased production of extracellular proteases. They also established that these phenotypes can be correlated with cytoxicity in both established cell lines and primary bone marrow derived osteoblasts and osteoclasts. Subsequent studies confirmed that, while multiple proteases appear to be involved, aureolysin plays the most important role in defining these phenotypes. This is consistent with the observation that eliminating the production of aureolysin most closely restored the proteome of a LAC sarA mutant to that of its isogenic parent strain. These results confirm that sarA controls the production and/or accumulation of virulence factors that limit both osteoblast and osteoclast function and thereby limit bone repair and induce reactive bone formation during the acute phase of S. aureus post-traumatic osteomyelitis. Furthermore, as with hematogenous osteomyelitis, there is an important role for S. aureus secreted proteases, most notably aureolysin, in the sarA mutant phenotype. To the extent that these changes compromise the local blood supply and consequently limit the efficacy of systemic antibiotic therapy, this suggests that inhibitors of sarA expression and/or function could be used to therapeutic advantage in an orthopaedic context.