, 2010), and SrrAB (Yarwood et al., CH5424802 manufacturer 2001). Many of these regulators are presumed

to affect Agr expression indirectly; however, some [CodY (Majerczyk et al., 2010), SrrA (Pragman et al., 2004) and SarA (Heinrichs et al., 1996)] have been shown to directly bind to the Agr locus. It is intriguing that many of these regulators are involved in modulating metabolic adaptation to various environments (CodY, CcpA, Rsr, and SrrAB) given the apparent increase in fitness associated with USA300 (Herbert et al., 2010) (see below). Though, any one of these or other unknown regulatory systems may be responsible for enhanced Agr activity in USA300; therefore, investigations into strain-specific differences in activity among these regulators click here may prove enlightening. For instance, SarA positively affects

Agr expression (Cheung & Projan, 1994; Reyes et al., 2011), and deletion of sarA in USA300 leads to drastic reductions in Hla and PSM levels (Weiss et al., 2009; Zielinska et al., 2011). However, recently, it was demonstrated that the loss of cytolytic expoprotein expression in the ∆sarA mutant was attributed to the resulting overproduction of extracellular proteases and not because of altered exoprotein gene transcription (Zielinska et al., 2011). While trans-acting regulators may prove to be major influences on USA300 Agr activity, cis-acting polymorphisms may also be involved. RNAIII transcripts among sequenced ST8 isolates are 100% conserved, but there is a single nucleotide polymorphism (SNP) 3 bp upstream of a known AgrA binding site within the RNAIII promoter that is only found among USA300 isolates. While this is the only SNP among ST8 and ST1 clones specific to USA300, other sites of variation exist when compared to USA100 and USA200 promoter sequences. SNPs in the Hla promoter were recently shown to drive its overexpression in bovine isolates by modulating SarZ binding (Liang et al., 2011). It remains to be determined whether SNPs in the RNAIII promoter

region of USA300 isolates affect expression leading to high Agr activity. Regardless of the mechanism behind hyperactive toxin production in USA300, it is important to remember that similar high-level expression is observed in the HA-MRSA progenitor clone, USA500. Thus, while the high virulence potentials of MycoClean Mycoplasma Removal Kit USA300 and USA500 may result from overproduction of exoproteins, this phenomenon alone cannot fully explain the enormous success of USA300 in human disease. The evolutionary forces that drive diversification in S. aureus have been recently examined, in part, because of the availability of more than 15 published S. aureus genome sequences. While a significant level of divergence is achieved through acquisition of MGEs, variability within the S. aureus core genome (~ 2000 orthologous genes shared among most S. aureus strains) is primarily generated through mutation (Feil et al., 2003; Kuhn et al., 2006).