Hososaka Yasuko, Hanaki Hideaki, Endo Harumi, Suzuki Yumiko, Nagasawa Zenzo, Otsuka Yoshihito, Nakae Taiji, Sunakawa Keisuke
Kitasato Research Center for Anti-infection Drugs, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan.
J Infect Chemother. 2007 Apr;13(2):79-86. doi: 10.1007/s10156-006-0502-7. Epub 2007 May 8.
Methicillin-resistant Staphylococcus aureus (MRSA) has been defined as S. aureus having the mecA gene or showing a minimum inhibitory concentration (MIC) of oxacillin higher than 4 mg/l. However, some clinical isolates are mecA-positive and oxacillin-susceptible. Therefore, we surveyed the occurrence of S. aureus having the mecA gene and an MIC of oxacillin of less than 2 mg/l (oxacillin-susceptible MRSA; OS-MRSA) in a total of 480 strains of S. aureus collected from 11 hospitals in different location in Japan isolated from 2003 through 2005. We found 6 strains matching the criteria for OS-MRSA. All 6 strains were staphylococcal cassette chromosome (SCC) mec-positive, without exception, and 4 strains showed the SCCmec type III-variant, which is unique in Japan. These OS-MRSAs were least resistant to oxacillin among the MRSAs tested and they were within the susceptible range to seven other beta-lactam antibiotics tested. Thus, OS-MRSA may become a high-resistant MRSA upon the treatment of patients with beta-lactam antibiotics. To characterize whether these OS-MRSAs were hospital-acquired or community-acquired MRSAs, we tested for the presence of the genes encoding toxins. Genes encoding hemolysin, exfoliative toxin, enterotoxin, toxic shock syndrome toxin-1, and Panton-Valentine leukocidin were found in 6, 4, 0, 0, and 0 strains, respectively. These results revealed that OS-MRSAs could be classified as a new type of MRSA that exhibits properties distinguishable from either hospital- or community-acquired MRSA. Coagulase typing of the OS-MRSAs supported the above conclusion. In this study, the occurrence of OS-MRSA at a certain frequency was noted; precautions are called for in the classification of oxacillin-resistant S. aureus and in the treatment of OS-MRSA infection.
耐甲氧西林金黄色葡萄球菌（MRSA）被定义为具有mecA基因或对苯唑西林的最低抑菌浓度（MIC）高于4mg/L的金黄色葡萄球菌。然而，一些临床分离株mecA呈阳性但对苯唑西林敏感。因此，我们对2003年至2005年从日本不同地区的11家医院收集的总共480株金黄色葡萄球菌中具有mecA基因且苯唑西林MIC小于2mg/L（苯唑西林敏感的MRSA；OS-MRSA）的金黄色葡萄球菌的出现情况进行了调查。我们发现6株符合OS-MRSA标准。所有6株均无一例外为葡萄球菌盒式染色体（SCC）mec阳性，4株显示SCCmec III型变体，这在日本是独特的。这些OS-MRSA在测试的MRSA中对苯唑西林的耐药性最低，并且对测试的其他七种β-内酰胺类抗生素处于敏感范围内。因此，在用β-内酰胺类抗生素治疗患者时，OS-MRSA可能会变成高耐药性MRSA。为了确定这些OS-MRSA是医院获得性还是社区获得性MRSA，我们检测了编码毒素的基因的存在情况。分别在6株、4株、0株、0株和0株中发现了编码溶血素、剥脱毒素、肠毒素、中毒性休克综合征毒素-1和杀白细胞素的基因。这些结果表明，OS-MRSA可被归类为一种新型的MRSA，其表现出与医院获得性或社区获得性MRSA不同的特性。OS-MRSA的凝固酶分型支持了上述结论。在本研究中，注意到OS-MRSA以一定频率出现；在耐苯唑西林金黄色葡萄球菌的分类以及OS-MRSA感染的治疗中需要采取预防措施。
