Phenotypic characterization of sarR mutant in Staphylococcus aureus

Multiple factors of Staphylococcus aureus are involved in infection. Expression of these factors is controlled by multiple regulatory systems such as, the Sar family of transcriptional regulators. The staphylococcal specific Sar family of proteins are involved in expression of numerous target genes involving virulence, autolysis, biofilm formation, antibiotic resistance, oxidative stresses, and metabolic processes. Genetic and biochemical characterization of several sar family genes have been studied. However, less is known about the phenotypic properties of the sar family mutants, except sarA mutant in S. aureus. In this report, various studies such as phenotype microarray, autolytic, hemolytic, protease and DNase assays were performed to study the phenotypic properties of sarR mutant, a member of the sar family mutants. Phenotypic microarray for growth kinetic analysis identified eight substances (e.g., chlorhexidine, ceslodin, 3,5-dinitrobenzene, plumbagin, minocycline, dipeptide Arg-Ser, phenylarsine oxide and piperacillin), whose mode of actions were more specific towards cell wall or membrane. These findings were confirmed by various independent growth study experiments. Overall, the results from various phenotypic assays such as growth kinetics, autolysis, protease and DNase suggest that a sarR mutant strain is more sensitive to autolytic activities compared to the wild type, while less sensitive with respect to a sarA mutant strain.