Regulation of biofilm and antibiotic-resistance by the modulator of SarA (msa) in Staphylococcus aureus

Antony Schwartz

Abstract

Staphylococcus aureus is an important human pathogen that is the causative agent of life-threatening diseases such as endocarditis and osteomyelitis. The ability of S. aureus to thrive as a successful pathogen can be partially attributed to its ability to form biofilm. Biofilm is an extracellular polysaccharide, protein, and DNA-based slime layer that protects the bacterial community. The global regulator sarA is essential for biofilm formation. Since the modulator of sarA (msa ) gene regulates several virulence factors and is required for the full expression of sarA, the capacity of the msa mutant to form a biofilm was examined. The mutation of msa results in reduced expression of sarA, and the msa mutant formed a weak and unstable biofilm. The msa mutant is able to adhere to surfaces and begins to form biofilm, but fails to mature indicating that the defect of the msa mutant biofilm is in the accumulation stage but not in primary adhesion. This finding is significant because it identifies a new gene that plays a role in the development of biofilm. Antibiotic resistance in Staphylococcus aureus has become an issue of paramount importance as the rate of MRSA (Methicillin-Resistant Staphylococcus aureus )-related deaths have surpassed HIV-related deaths in the United States over the last decade. In this study, mutation of the msa gene leads to increased susceptibility (MIC 3 μg/ml) to oxacillin in comparison to wild type MRSA strain COL (MIC 1600 μg/ml). RT-qPCR analysis was utilized to identify the genes that were differentially expressed. Apart from the fem genes, genes such as aux14, sigB, mecA, murAB and mraY were all differentially expressed in the msa mutant in comparison to the wild type strain COL. Additional functional assays and TEM studies show that the bacterial cell wall is compromised upon mutation of msa. The results from this study collectively indicated that msa plays an important role in antibiotic resistance by regulating cell wall and cell wall-precursor synthesis. Given these results and the possibility that Msa is a membrane protein, it is possible that Msa could serve as a target for therapeutic agents designed against Staphylococcus aureus.