| Research Abstract |
We have determined entire nucleotide sequences of SCCmecs in three MRSA strains, CA05 and 8/6-3P which were isolated from Chicago Children's Hospital, U.S.A, and 81/108 which was isolated form an outpatient in Japan. The SCCmecs of all three strains carried type-2 ccr A, B genes, and class B mec gene complex composed of IS1272-ΔmecRI-mecA-IS431. The J-regions of three SCCmecs(the region except ccr gene complex and mec gene complex in SCCmec) were not identical and differed from previously reported three SCCmecs(type-I, II, and III). Therefore, we have designated the SCCmec of CA05 as typeIVa, that of 8/6-3P as typeIVb, and 81/108 as typeIVc respectively. By PCR experiment, we found that three methicilin-susceptible type strains, S. hominis, S. arlettae, and S. arincularis, carried ccr genes. We selected a strain, S. hominis GIFU12263, determined the nucleotide sequence around ccr gene of the strain, and identified an unique structure designated SCC_<12263>. We consider that SCC_<12263> is an active primordial mobile genetic element for the Staphylococcal Cassette Chromosome mec (SCCmec). We have cloned ccrA1 and ccrB1 genes from S. hominis GIFU12263 as well as ccrA2 and ccrB2 genes from CA05 and 81/108. Those orfs were found to catalyze precise excision of the SCCmec from the methicillin-resistant staphylococci Type-I and Type-IV SCCmec could be transduced from MRSA into MSSA. However, conjugative transfer of SCCmec was not proved yet.
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