Yamashita K, Takarada Y, Li L, Otsuka N, Kagawa S, Matsuoka A
Clinical Laboratory, Hyogo College of Medicine, Nishinomiya.
Rinsho Byori. 1994 Oct;42(10):1069-76.
Methicillin resistance in S. aureus is primarily due to the presence of the mec A gene. However, in addition to mec, the phenotypic expression of methicillin resistance requires the presence of an additional gene(s), fem A which is chromosomally encoded. Previous studies suggest an increase in the biochemical function of fem A gene products due to base substitutions in the region upstream of the fem A gene and in its coding frame. The partial nucleotide sequences of fem A regions in reference and clinical strains of S.aureus were therefore analyzed by PCR-direct solid-phase sequencing and suitable DNA probes. Amplified target DNAs of 251, 330 and 271 bp were resolved on ethidium bromide-stained gels and hybridized with DNA probes conjugated to alkaline phosphatase. In ATCC 12600 strain, a palindromic sequence was conserved in the region upstream of fem A. However, it was destroyed by the occurrence of mutations in other reference, and clinical strains tested regardless of whether they are methicillin-susceptible or resistant. Furthermore, in the coding frame of fem A, two missense mutations were present in MSSA and MRSA without any regularity. These findings suggest that mutations in the fem A region may not be a single factor essential for regulation of methicillin resistance, although fem A probably functions cooperatively with mec A.
金黄色葡萄球菌对甲氧西林的耐药性主要归因于mec A基因的存在。然而，除了mec基因外，甲氧西林耐药性的表型表达还需要存在另一个基因fem A，该基因由染色体编码。先前的研究表明，由于fem A基因上游区域及其编码框架中的碱基替换，fem A基因产物的生化功能增强。因此，通过PCR直接固相测序和合适的DNA探针分析了金黄色葡萄球菌参考菌株和临床菌株中fem A区域的部分核苷酸序列。扩增得到的251、330和271 bp的目标DNA在溴化乙锭染色的凝胶上进行分离，并与碱性磷酸酶偶联的DNA探针杂交。在ATCC 12600菌株中，fem A上游区域的一个回文序列是保守的。然而，在其他测试的参考菌株和临床菌株中，无论它们对甲氧西林敏感还是耐药，该序列都因突变而被破坏。此外，在fem A的编码框架中，甲氧西林敏感金黄色葡萄球菌（MSSA）和耐甲氧西林金黄色葡萄球菌（MRSA）中存在两个错义突变，且无任何规律。这些发现表明，fem A区域的突变可能不是调节甲氧西林耐药性的唯一关键因素，尽管fem A可能与mec A协同发挥作用。
