Mobile genetic elements of Staphylococcus aureus

Abstract

Bacteria such as Staphylococcus aureus are successful as commensal organisms or pathogens in part because they adapt rapidly to selective pressures imparted by the human host. Mobile genetic elements (MGEs) play a central role in this adaptation process and are a means to transfer genetic information (DNA) among and within bacterial species. Importantly, MGEs encode putative virulence factors and molecules that confer resistance to antibiotics, including the gene that confers resistance to beta-lactam antibiotics in methicillin-resistant S. aureus (MRSA). Inasmuch as MRSA infections are a significant problem worldwide and continue to emerge in epidemic waves, there has been significant effort to improve diagnostic assays and to develop new antimicrobial agents for treatment of disease. Our understanding of S. aureus MGEs and the molecules they encode has played an important role toward these ends and has provided detailed insight into the evolution of antimicrobial resistance mechanisms and virulence.

Fig. 1

Horizontal and vertical gene transfer

Fig. 2

Acquisition of MGEs by S. aureus. 1 Incorporation of plasmids or plasmid elements into genomic DNA. 2 Plasmids can be maintained as free circular DNA. 3 Suicide plasmid. 4 Transfer of a transposon or an insertion sequence between plasmid and genomic DNA. 5 Transfer of a transposon or an insertion sequence between plasmids within the cell. 6 Transfer of a transposon or an insertion sequence from genomic DNA to another plasmid

Fig. 3

Linear schematic of the USA300 genome (strain FPR3757) and its major MGEs. a Genome. SCC_mecIVa encodes methicillin resistance. νSAα encodes lpl, ssl and νSAβ encodes lukDE, spl, bsa. SaPI5 encodes seq2 and sek2, φSA2USA300 encodes lukS/F-PV, and φSA3USA300 encodes sak and chip. b Plasmids of FPR3757. pUSA03 contains genes encoding resistance to mupirocin (ileS) and MLS_B (ermC). pUSA02 encodes resistance to tetracycline (tetK). pUSA01 is a cryptic plasmid

Fig. 4

Comparison of S. aureus SCCmec types. Class A SCCmec contains a complete mecA regulon (mec1-mecR1-mecA). Class B and class C SCCmec contain regulatory genes that are disrupted by IS, IS1272-ΔmecR1-mecA and IS431-ΔmecR1-mecA, respectively. Tn554 encodes erythromycin (ermA) and streptomycin/spectinomycin resistance (aad9 or spc); copA encodes a putative copper-transport ATPase; hsdR, hsdM, and hsdS encode a partial restriction-modification system (RM) type I; Tn4001 encodes an aminoglycoside resistance operon (aacA-aphD); plasmid pT181 encodes tetracycline resistance (tet); ΨTn554 encodes cadmium resistance (cadB, cadC); and plasmid pUB110 encodes bleomycin (ble) and tobramycin resistance (ant4′). pls Plasmin‐sensitive surface protein