Molecular Epidemiology of Community-Associated and Hospital-associated Methicillin-resistant Staphylococcus aureus in a Japanese University Hospital

BACKGROUND: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has been reported in healthcare facilities worldwide. But details of CA-MRSA in Japanese healthcare facilities are rarely reported. The aims of this study are to know the distribution of CA-MRSA and healthcare-associated MRSA (HA-MRSA) with detailed molecular typing, and to assess the efficacy of infection control practice in a Japanese hospital. METHODS: From July to October in 2015, first MRSA isolate from each patient was collected in Juntendo University Hospital, Tokyo, Japan. MRSA strains were categorized as CA-MRSA and HA-MRSA according to the clinical definition of CDC. Detection of toxin genes and SCCmec typing were performed by PCR. Genetic relatedness among isolates was determined by pulsed-field gel electrophoresis (PFGE). Multilocus sequence typing was performed using whole genome sequencing data. RESULTS: A total of 102 MRSA strains were collected in the study period, and categorized as 34 CA-MRSA (33.3 %) and 68 HA-MRSA (66.7 %), respectively. Among the 73 strains isolated from hospitalized patients, 10 were CA-MRSA (13.7 %). Whereas among the 29 strains isolated in clinic, 5 were HA-MRSA (17.2 %). Three major types were as follows: ST8-SCCmec IV (n = 26, 25.5 %, CA: HA= 10: 16), ST5-SCCmec IIa (n = 17, 16.7 %, CA: HA= 5: 12), and ST1-SCCmec IVa (n = 13, 12.7 %, CA: HA= 6: 7). Among ST8-SCCmec IV strains, SCCmec IVl, originally reported in Japanese CA-MRSA, was found both in CA-MRSA and HA-MRSA (n = 11, 10.8 %, CA: HA= 5: 6). Only one ST772-SCCmec V strain carried Panton–Valentine leukocidin (PVL) gene. Two ST765-SCCmec IIa strains in CCU, 2 ST765-SCCmec IIa strains in a general ward, and 6 ST2764-SCCmec IVa strains in NICU showed genetic relatedness by PFGE, respectively. Especially, ST2764-SCCmec IVa was a clone originally reported as HA-MRSA in another Juntendo-affiliated hospital. CONCLUSION: CA-MRSA and HA-MRSA were comparably found both in hospital and clinic. Unique Japanese clones were found in this study, but it seemed impossible to distinguish CA-MRSA and HA-MRSA simply by ST-SCCmec typing. In contrast, transmission of MRSA rarely happened in hospital. This heterogenous population structure of MRSA suggested that conventional HA-MRSA had lost its predominance by sufficient infection control, resulting in relative increase of CA-MRSA in hospital environment. DISCLOSURES: All authors: No reported disclosures.