Four Community- associated MRSA isolates expressing high-level mupirocin resistance (MIC: greater then1024mg/L) were isolated from four sites of a diabetic patient and characterized for the genetic location of their resistance determinants and typed using pulsed-field gel electrophoresis (PFGE), SCCmec coagulase gene and multilocus sequence typing to ascertain their relatedness. The presence of genes for resistance to high-level mupirocin (mupA), tetracycline (tetK) and fusidic acid (far 1), Panton-Valentine leukocidin (PVL), accessory gene regulators (agr) and capsular polysaccharide (cap) were detected in PCR assays. They were resistant to kanamycin, streptomycin, tetracycline, fusidic acid and cadmium acetate. They harboured mupA, tetK, far1, PVL, agr 3 and cap8.
They had identical PFGE pattern, coagulase gene type, possessed type IV SCCmec element and belonged to sequence type 80 (ST80). In contrast, they had three different plasmid profiles consisting of (1) 28.0 and 26.0 kb, (2) 28.0, 21.0 and 4.0 kb, (3). 41.0 and 4.0 kb. Genetic studies located resistance to tetracycline, fusidic acid and cadmium acetate on the 28 kb plasmids and mupA on related non conjugative 26 kb and 21 kb plasmids. One of the 21-kb mupirocin resistance plasmids was derived from the 41 kb plasmid during transfer experiments. The emergence of high-level mupirocin resistance in ST80-SCCmec-IV MRSA clone demonstrates the increasing capacity of CA-MRSA clones to acquire resistance to multiple antibacterial agents.
The presence of different plasmid profiles in genetically identical isolates created difficulty in interpretation of typing results and highlighted the weakness of using plasmid analysis as a sole method for strain typing.
PMID: 19833783 [PubMed - as supplied by publisher]