title: Addition of thymidine to culture media for accurate examination of thymidine-dependent small-colony variants of methicillin-resistant Staphylococcus aureus: a pilot study.
abstract: Small-colony variants (SCVs) are slow-growing subpopulations of various auxotrophic bacterial strains. Thymidine-dependent SCVs (TD-SCVs) are unable to synthesize thymidine; hence, these variants fail to grow in a medium without thymidine. In this study, we used 10 TD-SCVs of Staphylococcus aureus, of which four strains possessed mecA. We compared the efficacy of a newly modified medium containing thymidine for the detection of TD-SCVs of methicillin-resistant S. aureus (MRSA) to the efficacy of routinely used laboratory media. We observed that none of the 10 TD-SCVs of S. aureus grew in Mueller-Hinton agar, and four TD-SCVs of MRSA failed to grow on all MRSA screening media, except for the ChromID™ MRSA medium. Laboratory tests conducted using medium with thymidine incorporated showed that thymidine did not affect the minimum inhibitory concentrations of oxacillin and cefoxitin for clinical isolates of S. aureus, and was able to detect MRSA, including TD-SCVs. These findings showed that thymidine-incorporated media are able to detect TD-SCVs of MRSA without altering the properties of other clinically isolated MRSA strains.
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Horiuchi
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan. Electronic address: ggatcc@shinshu-u.ac.jp.
authors.forename: Takehisa
authors.initials: T
authors.lastname: Matsumoto
authors.affiliation: Department of Biomedical Laboratory Sciences, School of Health Sciences, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ota
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Kasuga
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Negishi
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Yaguchi
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Mitsutoshi
authors.initials: M
authors.lastname: Sugano
authors.affiliation: Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Honda
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D002440:Cefoxitin / Q000494:pharmacology; D003470:Culture Media / Q000737:chemistry*; D006801:Humans; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000254:growth & development* / Q000302:isolation & purification* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology; D046915:Penicillin-Binding Proteins; D010865:Pilot Projects; D013203:Staphylococcal Infections / Q000382:microbiology; D013936:Thymidine / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D002440:Cefoxitin; D000362:Agar; D010068:Oxacillin; D013936:Thymidine
keywords: MRSA screening media; TD-SCVs of MRSA; Thymidine