Impact of sarA on Daptomycin Susceptibility of Staphylococcus aureus Biofilms In Vivo

Abstract

We used a murine model of catheter-associated biofilm formation to determine whether the mutation of the staphylococcal accessory regulator (sarA) has an impact on the susceptibility of established Staphylococcus aureus biofilms to treatment with daptomycin in vivo. The experiments were done with two clinical isolates, one of which (UAMS-1) was obtained from the bone of a patient suffering from osteomyelitis, while the other (UAMS-1625) is an isolate of the USA300 clonal lineage of community-acquired methicillin (meticillin)-resistant S. aureus. UAMS-1625 had a reduced capacity to form a biofilm in vivo compared to that of UAMS-1 (P ‫؍‬ 0.0015), but in both cases the mutation of sarA limited biofilm formation compared to that of the corresponding parent strain (P < 0.001). The mutation of sarA did not affect the daptomycin MIC for either strain, but it did result in increased susceptibility in vivo in the context of an established biofilm. Specifically, daptomycin treatment resulted in the clearance of detectable bacteria from <10% of the catheters colonized with the parent strains, while treatment with an equivalent daptomycin concentration resulted in the clearance of 46.4% of the catheters colonized with the UAMS-1 sarA mutant and 69.1% of the catheters colonized with the UAMS-1625 sarA mutant. In the absence of daptomycin treatment, mice with catheters colonized with the UAMS-1625 parent strain also developed skin lesions in the region adjacent to the implanted catheter. No such lesions were observed in any other experimental group, including untreated mice containing catheters colonized with the UAMS-1625 sarA mutant.

Effects of Low-Dose Amoxicillin on Staphylococcus aureus USA300 Biofilms

“…Three of these genes encode well-studied mediators of S. aureus biofilm formation and ␤-lactam resistance: atl (discussed above), sarA, and mecA. Mutations in sarA decrease S. aureus biofilm and increase antibiotic susceptibility both in vitro and in vivo (31,57), whereas mutations in mecA, which encodes penicillin binding protein 2a, impede resistance to ␤-lactam antibiotics (58). Several other genes identified in our screen have also been associated with biofilm formation (codY), ␤-lactam resistance (fmtC and vraR), or both processes (rsbU, rsbW, fmtA, and rsh) (4,10,16,(33)(34)(35)(36)(37)(38)(39).…”

Defining the Strain-Dependent Impact of the Staphylococcal Accessory Regulator ( sarA ) on the Alpha-Toxin Phenotype of Staphylococcus aureus

“…Based on a specific interest in musculoskeletal infection, much of our research has been directed toward defining the mechanistic basis for S. aureus biofilm formation, and these studies have led us to conclude that the staphylococcal accessory regulator (sarA) plays a primary role in this regard. Specifically, we have demonstrated that mutation of sarA in diverse clinical isolates, including those of the USA300 lineage of community-associated methicillin-resistant S. aureus (CA-MRSA), limits biofilm formation to a degree that can be correlated with increased susceptibility to functionally distinct classes of antibiotics under both in vitro and in vivo conditions (1,2,45,47,48). This suggests that sarA would be a viable target for the development of therapeutic agents capable of overcoming the intrinsic resistance of biofilm-associated infections.…”

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm

“…The limitations of the animal model include the small size, soft tissue instead of orthopaedic implantation, and limited diffusion of physiologic substances within the sequestrum of the catheter. The animal model is useful as a screening tool for antibiofilm activity in vivo [54,74,75], where the catheter serves as a sequestrum for localizing the bacterial inoculum and as a nidus for biofilm formation. Because of difficulty in applying coatings directly to the catheter, we modified the catheter-associated biofilm model by including an easily coated stainless steel wire.…”