Genetic organization of the downstream region of the mecA element in methicillin-resistant Staphylococcus aureus isolates carrying different polymorphisms of this region

We describe here the genetic organization of the mec element downstream of the mecA gene in 34 different methicillin-resistant Staphylococcus aureus ( MRSA) clinical isolates carrying 13 of the most frequent polymorphisms of m ecA and representing the major epidemic clones of MRSA. AII polymorphisms c arried three common genetic elements: the hypervariable region, a copy of I S431, and a unique 2-kb sequence (downstream constant segment, or dcs) for which no homologous sequences are found in data banks. Polymorphisms of the downstream region were shown to be caused by the presence of linearized pl asmids flanked by insertion sequences (pUB110 pT181, and pI258) and the aut onomous insertion sequence IS256.