Methicillin-resistant Staphylococcus aureus: The Deadly Superbug

Methicillin-resistant Staphylococcus aureus (MRSA), often referred to as the "deadly superbug" by the media, is currently a major epidemiological threat on a global scale. The adaptability of S. aureus to antibiotics led to the emergence of MRSA in 1961 in a hospital ward in the United Kingdom. S. aureus developed resistance to β-lactam antibiotics through the acquisition of the mecA gene, which is situated on a mobile genetic element known as staphylococcal cassette chromsome mec (SCCmec). The mecA gene encodes penicillin-binding protein 2a (PBP2a), which has a significantly reduced affinity for β-lactam antibiotics, thereby conferring β-lactam resistance. Although the first MRSA clones were hospital-associated (HA-MRSA), communityassociated MRSA (CA-MRSA) clones are now increasingly found throughout the world, affecting normally healthy individuals. MRSA accounts for greater than 50-80% of S. aureus isolates. The global emergence of MRSA has raised concern among public health officials. In fact, in year 2005, Centers for Disease Control and Prevention (CDC) estimated that the number of MRSA fatalities in the United States surpassed the number of deaths from AIDS and hurricane Katrina combined. Several preventative measures have been suggested, including: covering wounds, maintaining good personal hygiene, and avoiding sharing personal items that could facilitate the transmission of MRSA bacteria. As MRSA continues to affect individuals worldwide, it is essential that further research be conducted on the epidemiology of this deadly superbug. Although progress has been made, our current knowledge of the pathogenesis and the molecular evolution of MRSA and the number of available treatments for MRSA infections are limited. This review describes our current understanding of the key determinants of multidrug resistance, worldwide dissemination, and modes of transmission of MRSA bacteria. Also, this review highlights some of the most recent research findings, which could lead to the development of novel anti-MRSA therapeutics. In addition, some of the challenges that researchers currently face are also discussed. INTRODUCTION Staphylococcus aureus, discovered in the 1880s, is a major human pathogen that is commonly carried on the skin or nose of 20 to 30% of the healthy human population. Also known as “the golden staph,” S. aureus is a facultative anaerobic and gram-positive coccus characteristically identified by notable round, golden-yellow colonies. S. aureus is one of the most common causes of skin infections in the United States, and it has been shown to cause a wide range of illnesses, ranging from pimples and boils to bloodstream infections and pneumonia (Deurenberg, R. and Stobberingh, E., 2008; Gantz, N. et al., 2003). The remarkable success of S. aureus as a human pathogen could be attributed largely to its ability to develop antimicrobial resistance. Just two years after the introduction of penicillin for medical use, in 1942, the first penicillin-resistant S. aureus isolate was observed in a hospital. Since 1960, approximately 80% of all S. aureus strains have been found to exhibit penicillin-resistance (Deurenberg, R. and Stobberingh, E., 2008).