Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is defined by the presence of the mecA gene, which is considered to have been transferred horizontally from unknown bacterial species to S. aureus. As a candidate of evolutionary precursor of the mecA, the mecA-like gene (mecA homologue), which is ubiquitously present in Staphylococcus sciuri has been proposed. In this study, sequences of the mecA homologue in four S. sciuri strains (SCBM1–SCBM4) derived from dairy cows were determined to analyze their genetic characteristics and relatedness to mecA and the mecA homologue reported so far. The mecA-like gene sequences of the four S. sciuri strains were identical with each other and were considered to encode a product comprising 665 amino acids that is one amino acid smaller in size than products of mecA-like gene reported previously for S. sciuri strains K1, K11, and K3 (mecA1). The mecA homologue of a representative strain SCBM1 showed 79.3–79.8% sequence identity to MRSA mecA and 93.4–94.4% identity to mecA homologues reported for the three S. sciuri strains. Between S. sciuri strain SCBM1 and strains K1, K11, or K3, amino acid sequence identities in transpeptidase domain of the mecA-like gene product (98.2–98.5%) were higher than those in the transglycosylase domain (92.1–94.3%). In addition, SCBM1 showed extremely high sequence identities of hsp60, sodA, and rpoB genes (more than 98.7%) to S. sciuri strains, while showing 70.3–94.2% identity of these genes to other staphylococcal species. These findings indicated that mecA homologues in S. sciuri may be genetically more divergent than mecA in MRSA and methicillin-resistant coagulase-negative staphylococci.
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