FIG. 1.

Factors influencing the control of virulence of S. aureus include quorum regulation and now the nutritional quality of the environment (for reviews and more details, see references 21 and 30). Extracellular accumulation of the AgrD-derived thiolactone-containing peptide provides a mechanism for quorum regulation of virulence. However, as shown in the study by Majerczyk et al. (16), CodY influences the expression of RNAII and RNAIII from P2 and P3, respectively, limiting in the presence of BCAA and GTP the quorum activator of virulence and its effector, RNAIII. RNAIII, when made in response to quorum accumulation or when not repressed by CodY (such as in codY mutants or parental cells with low intracellular pools of GTP and BCAA), enhances both transcription and translation of alpha-toxin and other S. aureus toxins and exoproteins and also PIA/PNAG-associated biofilm formation.