Genomic Islands in Staphylococcus

Staphylococci are Gram-positive bacteria that have successfully evolved from a normal flora with limited threats to potentially life-threatening pathogens, particularly, Staphylococcus aureus. Species of staphylococci have adapted to survive under selective pressure mainly due to their ability to acquire mobile genetic elements (MGEs). Methicillin-resistant S. aureus is a common example of this successful evolution not only in hospital setting but also in the community. Recent literature supports that Coagulase-negative staphylococci including S. epidermidis are the reservoir for resistance as well as virulence-associated determinants for S. aureus. A wide range of MGEs are present in Staphylococci including genomic islands (GI), with staphylococcal chromosome cassette (SCCmec) as an example of the most common GI of medical importance, found in 15-20% of the S. aureus. The SCCmec are mobile entities that have been classified, so far into 14 types. Other GIs with similar characteristics to the SCC element is the Arginine Catabolic Mobile Element (ACME) and Copper and Mercury Resistance (COMER) that form a composite island with SCCmec IV, which have been first described in S. aureus USA-300 and in S. epidermidis as well. Other MGEs, include Insertion sequences and Transposons, plasmids, Integrative and conjugative elements (ICEs), and bacteriophages. MGEs have a significant survival advantage over their host species as these carry a wide variety of genes that confer resistance to antibiotics, heavy metals, and biocides.