Japanese Journal of Medical Technology
Online ISSN : 2188-5346
Print ISSN : 0915-8669
ISSN-L : 0915-8669
Technical Articles
Evaluation of two methicillin-resistant Staphylococcus aureus culture media in the detection of thymidine-dependent small colony variants of MRSA
Mitsuru NISHIOYuki MIYAKIYuriko OGAWATakato OSUGIAkira KOIKE
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2021 Volume 70 Issue 4 Pages 748-753

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Abstract

Small colony variants (SCVs) constitute a slow-growing subpopulation of bacteria with distinctive phenotypic and pathogenic traits. Phenotypically, SCVs have a typical colony morphology and unusual biochemical characteristics. Therefore, it is difficult to detect and identify SCVs. It is suggested that SCVs are not detected in the conventional screening agar for methicillin-resistant Staphylococcus aureus (MRSA). We compared growth performances of SCVs-MRSA in two culture media: CHROMagaer MRSA (CHROMagaer) and NISSUI plate X-MRSA agar (X-MRSA). We also compared the usefulness of these media with that of the medium used in a routine laboratory test. Method: (1) We examined the growth support ability by the Miles & Misra method. The strains used in the examination were isolates of three SCVs-MRSA strains and one normal MRSA strain and type strains of MRSA and MSSA. (2) For 50 clinical specimens, we compared the MRSA detectability. Result: (1) The growth support abilities of the two culture media were similar. One of the SCVs-MRSA strains required 48 h for growth in both culture media. The two other SCVs-MRSA strains showed the same growth as the normal MRSA in 24 h. (2) After 24 h of incubation, the sensitivity, specificity, positive predictive values (PPV), and negative predictive values (NPV) were all found to be 100% for the two culture media. After 48 h of incubation, the sensitivity, specificity, PPV, and NPV were 100, 91.7, 33.3, and 100 for CHROMagaer and 100, 93.8, 40.0, and 100 for X-MRSA, respectively. Conclusion: With the two culture media, the detectabilities of SCVs-MRSA and MRSA in a routine laboratory test were similar. We conclude that SCVs-MRSA can be easily detected using the two culture media.

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© 2021 Japanese Association of Medical Technologists
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