Antimicrobial resistance mechanisms of Staphylococcus aureus

The miracle of antibiotic discovery has been threatened by the emergence of superbugs. One of those superbugs, methicillin-resistant Staphylococcus aureus (MRSA) is now responsible for more deaths per year in the United States than HIV. The added healthcare costs for fighting MRSA infections is in the billions of dollars per year worldwide. Plus, the danger of not having effective antimicrobial therapy available is imminent. This added threat by these organisms includes the emergence of vancomycin-resistant S. aureus (VRSA), among other resistant strains (such as vancomycin-intermediate S. aureus – VISA, and borderline oxacillin-resistant S. aureus – BORSA). The MRSA strains, especially, have a growing diversity in the structure of the genetic element that confers resistance; the Staphylococcal cassette Chromosome mec (SCCmec), which carries the methicillin-resistance gene, mecA. These genetic elements also frequently carry resistance genes for other antimicrobials such as aminoglycosides (gentamicin, tobramycin) erythromycin and tetracycline. Certain strains of MRSA (hospital-acquired) are likely to carry antimicrobial resistance to additional drugs, including the fluoroquinolones.