Evaluation of agar culture plates to efficiently identify small colony variants of methicillin-resistant Staphylococcus aureus

• Published in: Infection and drug resistance 2019-06, Vol.12, p.1743-1748
• Main Authors: Watanabe, Yuji, Oikawa, Nozomi, Hariu, Maya, Seki, Masafumi
• Format: Article
• Language: English
• Subjects: Antibacterial agents; Antibiotics; Bacteremia; Bacteria; CHROMagar; Clinical isolates; Colonies; Comparative analysis; Culture media; Cystic fibrosis; Drug resistance; Hospitals; Identification; Intravenous administration; Ions; Lung diseases; Mass spectrometry; Methicillin; Microbial drug resistance; MS-CFS; Original Research; Pathogens; Pharmaceuticals; Scientific imaging; SCV-MRSA; Sheep; sheep blood agar; Staphylococcal infections; Staphylococcus aureus; Staphylococcus aureus infections; Staphylococcus infections; Streptococcus infections; Sulfamethoxazole; Surveillance; Thymidine; thymidine-dependent MRSA; Trimethoprim; X-MRSA
• ISSN: 1178-6973; 1178-6973
• DOI: 10.2147/idr.s207057

Small-colony variants of methicillin-resistant (SCV-MRSA) recently were described as slow-growing, thymidine-dependent strains; typically, SCV-MRSA were isolated from patients receiving sulfamethoxazole-trimethoprim, but detection of these strains frequently was delayed because of their small colony size and slow growth. Bacteremia cases due to SCV-MRSA sometimes become lethal when the initiation of treatment with intravenous anti-methicillin-resistant (MRSA) drugs starts too late. Here, we evaluated the use of general MRSA-specific agar plates in Japan, including MS-CFX, X-MRSA, and CHROMagar, for the efficient detection of SCV-MRSA, including the comparative detection efficiencies of these media for stock strains and clinical isolates. Among the three MRSA-specific agar plates that were tested, X-MRSA and CHROMagar showed similar detection efficiencies for both 24 and 48 hrs culturing; in contrast, MS-CFS did not permit the detection of SCV-MRSA in stock strains. For clinical isolates of SCV-MRSA, X-MRSA plates permitted detection of the smallest and slowest-growing colonies of SCV-MRSA at 48 hrs of culturing; in contrast, CHROMagar and MS-CFX sometimes did not identify SCV-MRSA at 24 and 48 hrs. Optimization of media and incubation times will be necessary for efficient identification for SCV-MRSA, which would prevent delays in diagnosis and treatment with anti-MRSA drugs.