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The Journal of the Japanese Society for Clinical Microbiology |
Biblioraphy Information
| ArticleTitle |
Discrepancies between mec gene presence and antimicrobial susceptibility testing in MRSA: insights from direct inoculation on screening media |
| Language |
J |
| AuthorList |
Tatsuki Mura1), Miyako Aso1), Kazumi Kanaya1), Kae Kawamura1), Masatoshi Taga2), Yoshitsugu Iinuma1,3) |
| Affiliation |
1) Department of Clinical Laboratory, Kanazawa Medical University Hospital
2) Department of Pharmacy, Kanazawa Medical University Hospital
3) Department of Infectious Diseases, Kanazawa Medical University |
| Publication |
J.J.C.M.: 36 (1), 31-37, 2025 |
| Received |
July 5, 2025 |
| Accepted |
October 15, 2025 |
| Abstract |
This study investigated the presence of the mec gene in methicillin-resistant Staphylococcus aureus (MRSA) strains, initially identified as MRSA, that exhibited susceptibility to either cefoxitin (CFX) or oxacillin (MPIPC). From March 2019 to December 2024, 40 isolates that showed the above sensitivity results were analyzed, with 10 found to be negative for the mec gene. Upon re-testing antimicrobial susceptibility, three of these 10 mec-negative isolates were re-confirmed as MRSA and were presumed to be borderline oxacillin-resistant S. aureus (BORSA). Conversely, the remaining seven isolates were re-identified as methicillin-susceptible S. aureus (MSSA), revealing a discrepancy in the results. Our findings suggest that inferring the presence or absence of the mec gene solely from antimicrobial susceptibility test (AST) results is challenging for MRSA strains displaying susceptibility to either MPIPC or CFX. However, direct inoculation of colonies onto MRSA screening agar effectively differentiated between mec-positive and mec-negative strains. Using the PBP2' latex test also yielded correct identification. While rare discrepancies between mec gene status and AST results have been reported, their epidemiology and underlying mechanisms remain unclear. Microbiology laboratories should consider integrating MRSA screening media, PBP2a detection latex agglutination tests, and genetic testing, in addition to conventional ASTs, and define appropriate conditions for their application. |
| Keywords |
MRSA, mecA, mecC, BORSA |
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