Blanc D S, Wenger A, Bille J
Hospital Preventive Medicine, Institute of Microbiology, University Hospital of Lausanne (CHUV), Lausanne, Switzerland.
J Clin Microbiol. 2003 Aug;41(8):3499-502. doi: 10.1128/JCM.41.8.3499-3502.2003.
A novel medium, Oxacillin Resistant Screening Agar (ORSA) medium, was evaluated for the screening of specimens for methicillin-resistant Staphylococcus aureus (MRSA) in the hospital setting. Screening swabs (swabs of the nose, throat, perineum, and infected sites) were inoculated onto the new ORSA medium and into an enrichment broth (Muller-Hinton broth supplemented with NaCl and oxacillin). After 24 h of incubation, the enrichment broth was subcultured onto one ORSA plate and one lipovitellin Chapman salt agar plate. The sensitivities for the detection of MRSA were calculated for each medium alone and for the media in combination. A low sensitivity (74%) was obtained when ORSA medium was used alone as a primary culture, whereas the sensitivity was 88% when a single selective enrichment broth was used. Among the 414 blue colonies observed on ORSA plates, only 47% were found to be MRSA, 40% were coagulase-negative staphylococci, 7% were Enterococcus species, and 2% were methicillin-sensitive S. aureus. The optimal incubation time for the ORSA plates was evaluated. On primary culture, 38% of the blue MRSA colonies were visible only after 48 h of incubation (no blue colonies were not seen after 24 h of incubation), whereas 94% of the colonies were already visible at 24 h when ORSA plates were used for subcultures. In conclusion, the advantage of the novel ORSA medium is the ease of recognition of mannitol-fermenting bacteria, but further identification tests are needed to confirm the identification of S. aureus. An enrichment broth is still needed to ensure a good sensitivity for the recovery of MRSA, and an incubation time of 48 h is required for primary culture on ORSA medium.
一种新型培养基——耐苯唑西林筛选琼脂（ORSA）培养基，在医院环境中用于筛选耐甲氧西林金黄色葡萄球菌（MRSA）标本的评估。将筛选拭子（鼻、咽、会阴及感染部位的拭子）接种到新的ORSA培养基上，并接种到增菌肉汤（添加氯化钠和苯唑西林的穆勒-欣顿肉汤）中。培养24小时后，将增菌肉汤转种到一块ORSA平板和一块卵黄磷壁酸查普曼盐琼脂平板上。分别计算每种培养基单独使用以及联合使用时检测MRSA的敏感性。单独使用ORSA培养基作为初代培养时敏感性较低（74%），而使用单一选择性增菌肉汤时敏感性为88%。在ORSA平板上观察到的414个蓝色菌落中，仅47%被发现为MRSA，40%为凝固酶阴性葡萄球菌，7%为肠球菌属，2%为甲氧西林敏感金黄色葡萄球菌。对ORSA平板的最佳培养时间进行了评估。在初代培养时，38%的蓝色MRSA菌落在培养48小时后才可见（培养24小时后未见蓝色菌落），而当ORSA平板用于转种培养时，94%的菌落在24小时时已经可见。总之，新型ORSA培养基的优点是易于识别甘露醇发酵菌，但需要进一步的鉴定试验来确认金黄色葡萄球菌的鉴定。仍需要增菌肉汤以确保对MRSA的回收具有良好的敏感性，并且在ORSA培养基上进行初代培养需要48小时的培养时间。
