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Updated: Dec 2, 2025
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Clinical characteristics and molecular analysis of USA300 and ST 764 methicillin-resistant Staphylococcus aureus
Shinji Ogihara1, Osamu Inoue2, Takaya Yamagami3
1Department of Clinical Laboratory, University of Yamanashi Hospital, 1110, Shimokato, Chuo-shi, Yamanashi, 409-3898, Japan; Division of Infection Control and Prevention, University of Yamanashi Hospital, 1110, Shimokato, Chuo-shi, Yamanashi, 409-3898, Japan; Department of Clinical and Laboratory Medicine, Faculty of Medicine, University of Yamanashi, 1110, Shimokato, Chuo-shi, Yamanashi, 409-3898, Japan.
Introduction:
USA300 is the most common community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strain. Sequence type (ST) 764 MRSA is a new local variant of the ST 5 lineage. The objective of this study was to determine the clinical characteristics of USA300 and ST 764 infections among outpatients in Japan.
Methods:
We obtained MRSA isolates from 132 outpatients who visited our hospital from January 2016 to December 2017 and compared USA300 infection group to ST 764 infection group. Molecular analysis, including that of various toxins and other virulence factors, of the MRSA isolates were performed. In particular, we investigated the relationships among PCR-based open reading frame typing (POT) scores, MRSA clones, and virulence factors.
Results:
Twenty-seven USA300 isolates (20.5%) and 16 ST 764 isolates (12.1%) were identified. Although USA300 and ST 764 had lower rates of risk factors, their infection rates were higher. USA300-infected patients had higher rates of deep skin and soft tissue infections compared with the non-USA300 CA-MRSA-infected patients. Notably, the USA300 and ST 764 isolates had unique POT scores.
Conclusions:
Our results indicated that USA300 MRSA was spreading in an area 120 km west of Tokyo, Japan. We observed multiple cases of ST 764 MRSA infection, raising concerns about the antimicrobial resistance of ST 764, as it limits the choices of antibiotics to treat infection. The POT score can predict the presence of toxins and virulence factors, as well as the clone identity of MRSA with high accuracy.
