STAPHYLOCOCCAL ACCESSORY REGULATOR (SAR) IN CONJUNCTION WITH AGR CONTRIBUTES TO STAPHYLOCOCCUS-AUREUS VIRULENCE IN ENDOPHTHALMITIS

Previous studies showed that an agr mutant strain of Staphylococcus au reus was partially attenuated in virulence compared to a parental stra in in experimental endophthalmitis. Tile purpose of this study was to determine whether the sar locus, either alone or through interactions with agr, contributes to the regulation of virulence in S. aureus endo phthalmitis. Experimental endophthalmitis was established by the midvi treous injection of approximately 30 CFU of S. aureus RN6390 or the is ogenic attenuated strains RN6311 (agr mutant), ALC136 (sar mutant), an d ALC135 (agr sal double mutant). Unexpectedly, the rate of reduction in electroretinographic B-wave amplitude in eyes infected with strain ALC136 (sal mutant) was not significantly different from the parental strain on postinfection day (PID) 5 (10% retention). In contrast, ALC1 35 (agr snr double mutant)infected eyes retained 73% of preoperative B -wave amplitude on PID 5. Therefore, unlike a,or; a mutation in the sa r locus alone does not alter the overall virulence of wild-type S. aur eus in experimental endophthalmitis. However, the combined effect of i nsertional mutations in both the snr. and agr global regulators leads to near-complete attenuation of virulence.