Increase in the frequency of community-acquired methicillin-resistant Staphylococcus aureus clones among inpatients of acute care hospitals in the Kyoto and Shiga regions, Japan.

Background: Specific epidemic clones of hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) are responsible for the worldwide spread of MRSA. However, in recent years, the isolation of community-acquired MRSA (CA-MRSA) clones has been increasing. We investigated the latest molecular epidemiology trends of HA-MRSA and CA-MRSA clones in the Kyoto and Shiga regions, Japan.

Materials And Methods: All nonduplicate MRSA isolates obtained from the clinical specimens of inpatients at four acute care hospitals in the Kyoto and Shiga regions between 2014 and 2019 were typed using the PCR-based open reading frame typing (POT) method. CA-MRSA and HA-MRSA were classified according to the POT1 values. We performed whole-genome sequencing analysis for representative isolates displaying common POT types.

Results: A total of 2413 isolates were included in the study, comprising 1730 nosocomial and 683 nonnosocomial isolates. The rates of HA-MRSA decreased from 50.2% in 2014 to 19.0% in 2019, while those of CA-MRSA increased from 44.7% to 76.4% (p < 0.001). Isolates belonging to the most common 10 POT types (CA-MRSA, n = 6; HA-MRSA, n = 4) accounted for 42% of the isolates studied and were obtained from 3 or more hospitals. Whole-genome sequencing analysis showed that the common CA-MRSA isolates with POT types 106-137-80, 106-9-80, 106-9-2, and 106-137-2, those with POT types 106-183-37 and 106-129-5, and HA-MRSA isolates with POT types 93-191-103, 93-157-127, 93-137-103, and 93-223-111 belonged to ST8-SCCmecIV, ST1-SCCmecIV, and ST764-SCCmecII, respectively.

Conclusion: A recent clonal shift from HA-MRSA to CA-MRSA occurred, and specific regional clones were prevalent among inpatients in the Kyoto and Shiga regions.