Novel methicillin resistance gene mecD in clinical Macrococcus caseolyticus strains from bovine and canine sources

Methicillin-resistant Macrococcus caseolyticus strains from bovine and canine origins were found to carry a novel mecD gene conferring resistance to all classes of β-lactams including anti-MRSA cephalosporins. Association of β-lactam resistance with mecD was demonstrated by gene expression in S. aureus and deletion of the mecD -containing island in M. caseolyticus . The mecD gene was located either on an 18,134-bp M. caseolyticus resistance island (McRI mecD -1) or a 16,188-bp McRI mecD -2. Both islands were integrated at the 3′ end of the rpsI gene, carried the mecD operon ( mecD-mecR1 m -mecI m ), and genes for an integrase of the tyrosine recombinase family and a putative virulence-associated protein ( virE ). Apart from the mecD operon, that shared 66% overall nucleotide identity with the mecB operon, McRI mecD islands were unrelated to any mecB -carrying elements or staphylococcal cassette chromosome mec . Only McRI mecD -1 that is delimitated at both ends by direct repeats was capable of circular excision. The recombined excision pattern suggests site-specific activity of the integrase and allowed identification of a putative core attachment site. Detection of rpsI -associated integrases in Bacillus and S. aureus reveals a potential for broad-host range dissemination of the novel methicillin resistance gene mecD .