Molecular Typing of ccrB Gene in Methicillin-resistant Staphylococcus aureus by Restriction Fragment Length Polymorphism

Abstract

Staphylococcus aureus is considered as one of the most essential bacterial pathogens in humans that can cause various infections in patients ranging from skin infections to fatal necrotizing pneumonia, bacteremia, and endocarditis (1). Methicillin-resistant S. aureus (MRSA) is one of the important pathogens that is responsible for many nosocomial infections. First, MRSA was identified only in the hospitals, but 30 years later, the first virulent MRSA was acquired from the community (2). The resistance to methicillin in S. aureus is induced by the presence of the mecA gene, encoding low-affinity penicillin-binding protein PBP2a (78 KD) (3,4). MRSA has a mobile genetic element staphylococcal cassette chromosome mec (SCCmec) carrying the mecA gene. (5-7) SCCmec elements in S. aureus are as unique genomic islands with 2 essential components (i.e., the ccr and the mec gene complexes) and J region (5,8,9). The ccr gene complex is composed of ccr genes encoding 2 sitespecific recombinases (ccrA and ccrB), and the mecA gene complex contains mecA and regulatory genes mecI and mecR. (6,10,11) Zhang et al defined 8 different types of SCCmec in the combination of ccr and mec complex. While types I-V were widespread (12), other types existed in the strains of the country from which they were originated (13,14). SCCmec exchange between species is related to the ccr gene expression (15). Several allotypes of ccr and mec gene are classified in SCCmec. The 5 allotypes of the ccr gene complex include ccrAB1, ccrAB2, ccrAB3, ccrAB4, and ccrC (16,17), and 5 classes of the mec gene complex (types I-V) were described and SCCmec type IV has 8 individual subtypes (18,19).The site-specific recombination of SCCmec is catalyzed by its encoded ccr recombinases, ccrA and ccrB for types I to IV and ccrC for type V. In addition, ccrA and ccrB belong to a family of large serine invertase and resolvases