Staphylococcal Cassette Chromosome mec (SCC mec ) Typing of Methicillin-Resistant Staphylococcus aureus Strains Isolated in 11 Asian Countries: a Proposal for a New Nomenclature for SCC mec Elements

Abstract

ABSTRACT A description of staphylococcal cassette chromosome mec (SCC mec ) elements carried by 615 methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in 11 Asian countries is reported, and a novel nomenclatural system based on their structures is proposed. The 615 strains were classified as type 3A (370 strains), type 2A (207 strains), type 2B (32 strains), type 1B (1 strain), and nontypeable (5 strains). The previously reported type III SCC mec (DDBJ/EMBL/GenBank accession no. AB037671) carried by the MRSA strain 85/2082 was ascertained to be composed of two SCC elements, type 3A SCC mec and SCC mercury . PCR analysis indicated that 310 of 370 type 3A SCC mec strains carried both SCC elements. These strains were prevalent in eight countries: Thailand, Sri Lanka, Indonesia, Vietnam, Philippines, Saudi Arabia, India, and Singapore. The remaining 60 type 3A SCC mec strains differed with respect to the left extremity polymorphism or to the presence of ccrC . Among these, two were identified as carrying only type 3A SCC mec elements, but their left extremities differed. Type 2A SCC mec strains predominated in Korea and Japan, although the frequency of the presence of ant ( 4 ′)-1 gene downstream of mecA varied (53% for Korean strains; 93% for Japanese strains). Various SCC mec elements were identified in the tested strains, and limited numbers were identified by their multilocus sequence typing genotypes. These data suggest that numerous MRSA clones are disseminated in Asian hospitals, and these consist of minor clones that are presumed to have arisen locally and major clones that are presumed to have been introduced from other countries.