Clonal Diversity and Genetic Characteristics of Methicillin-Resistant Isolates from a Tertiary Care Hospital in Japan.

Molecular epidemiological characteristics were investigated for 1,041 isolates of methicillin-resistant (MRSA) collected in a tertiary care hospital in northern Japan for a 4-year period (2011-2014). Genotypes (staphylococcal cassette chromosome [SCC], sequence type, , , etc.) and the presence of drug resistance/virulence factor genes in the isolates were analyzed by multiplex/uniplex PCR, and PCR-direct sequencing as needed. Among these MRSA, predominant SCC type was IIa (87.2%), followed by IV (10.1%) and V (1.2%). The SCC IIa-MRSA belonged to coagulase genotype () IIa and ST5/ST764, which are known as major health care-associated-MRSA (HA-MRSA) in Japan (New York/Japan clone) and its variant. Panton-Valentine leucocidine (PVL) genes were detected in only five isolates (0.5%) with genotypes ST8-SCC IVa/-t008/-IIIa (USA300 clone), ST6-SCC IVb, and ST59-SCC V (Taiwanese clone). Arginine catabolic mobile element (ACME) type I and II' were identified in three and five isolates of ST8-SCC IVa and ST764-SCC IIa MRSA, respectively. PVL-/ACME- isolates were classified into various STs/clonal complexes (CCs), with CC1, CC5, CC8, CC89, and CC121 being common. It was notable that SCC IVl was the most common among SCC IV subtypes, and was carried by almost half of -IIIa isolates (47%, 34/72) without PVL genes, which represented the novel ST8 MRSA clone spreading in Japan (, "ST8/CA-MRSA/J"). Uncommon MRSA clones in Japan, ST72-SCC IV (South Korean clone), ST398 livestock-associated clone, and ST20 bovine-associated MRSA, were identified. Furthermore, we isolated PVL-negative ST8-SCC I/-IIIa and ST81-SCC V/-VIIa MRSA, which were considered presumptive novel clones. The present study revealed the genetic diversity of HA-MRSA, including potentially emerging clones of putative different origins.