Identification of staphylococcal cassette chromosome mec encoding methicillin resistance in Staphylococcus aureus isolates at Charles Nicolle Hospital of Tunis

Abstract

Staphylococcal cassette chromosome is a mobile element that carries the gene mecA mediating the methicillin resistance in staphylococci. In Staphylococcus aureus five types of SCC mec have been described, which differs in size and genetic composition among strains. SCCmec typing of 34 non redundant methicillin-resistant S. aureus (MRSA) recovered in 2004 at Charles Nicolle Hospital of Tunis was carried out. The isolates were identified by conventional methods. Methicillin resistance was detected by oxacillin and cefoxitin disks and confirmed by mecA PCR. The SCC mec complex types were determined by using PCR which amplify a sequence overlapping the right SCC mec chromosome junction. Strains were recovered mainly from cutaneous pus (61.7%) and blood cultures (17.64%). They were isolated from different wards: medicine (53.1%) especially from dermatology (41.2%); surgery (40.6%) and pediatrics (3.1%). Only two strains were community-acquired MRSA. Two strains (5.9%) were harboring SCC mec type I; five (14.7%) SCC mec type II and 27 (79.4%) SCC mec type III. The two community-acquired MRSA were harboring type II and III SCC mec, usually found in hospital acquired MRSA. Our findings indicate that there are only three SCC mec types at Charles Nicolle Hospital. However, the existence of SCC mec types II and III in community incite us to investigate more community-acquired MRSA.