The staphylococci

The staphylococci are opportunistic pathogens and a major cause of hospital- and community-acquired infections ranging in severity from minor skin infections to widespread life-threatening infections. The occurrence of highly virulent community-acquired Staphylococcus aureus (CASA) and continued progression of resistance to multiple antimicrobials, including vancomycin, marks a re-emergence of the staphylococci as serious health care threat. Multiple genomes of the two major staphylococcal pathogens, S. aureus and Staphylococcus epidermidis, have been sequenced (genomes of seven S. aureus isolates and two S. epidermidis isolates). Comparative analysis of these genomes has shown that they are syntenic along their length and share a core set of genes with roles in metabolism and general housekeeping functions. Nonsyntenic regions contain species-specific genes and pathogenicity genomic islands, including bacteriophages, which are the primary source of variations in pathogenicity and resistance. Overall differences in pathogenicity between the two species can be attributed to genome islands in S. aureus, which encode exotoxins, leukocidins, and leukotoxins not found in S. epidermidis. Gene transfer among staphylococci and with other low GC gram-positive bacteria has contributed to the evolution of resistance and virulence and is likely playing a role in the emergence of increasingly virulent members of the staphylococcal family.

Keywords: Staphylococcus aureus; Staphylococcus epidermidis gene transfer; virulence; resistance