Genetic and Molecular Mechanisms Associated with Antibiotic Resistance in Methicillin Resistant Staphylococcus aureus (MRSA): A Review

Abstract

Methicillin Resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. It is still one of the major problems of drug resistance and it should be a frequent and an important human pathogen both in community and in hospital. Methicillin - resistant Staphylococcus aureus (MRSA) has been known among the most important and intimidating bacteria involved in hospital infections in humans. MRSA resistance to methicillin has been attributed to a number of mechanisms, but the chief factor is reckon as its ability to produce specific binding protein 2a (PBP-2a) which renders β - lactamase resistant penicillins ineffective including all other β- lactam drugs. The Penicillin Binding Protein 2 has shown a usual low binding affinity for almost all beta - lactam antibiotics as compared to native PBPs. The Penicillin Binding Protein 2a (PBP2a) is coded and induced by the mec A gene a part of Staphylococcal cassette chromosome (SCCmec). The SCCmec is known to be present in MRSA but not in the MSSA strains. SCCmec is shown to be located in exactly the same region between spa and purA in the S. aureus chromosome. Another chromosomal gene called femA, working with mecA gene is required for the expression of MRSA and this gene is found to be absent in other Staphylococcus species giving S. aureus special feature to differentiate from other Staphylococci. Apart from mec A gene, a number of environmental and genetic factors have also shown to influence the methicillin resistance. The paper review the genetic and molecular mechanisms associated with beta - lactam antibiotics in MRSA.