Couto I, de Lencastre H, Severina E, Kloos W, Webster J A, Hubner R J, Sanches I S, Tomasz A
Molecular Genetics Unit, Universidade Nova de Lisboa, Oeiras, Portugal.
Microb Drug Resist. 1996 Winter;2(4):377-91. doi: 10.1089/mdr.1996.2.377.
In an effort to explore the origin and/or reservoirs of the genetic determinant(s) of methicillin resistance in Staphylococcus aureus, we examined over 200 strains representing 13 different species within the genus Staphylococcus for the presence of the mecA gene, using a DNA probe internal to this gene prepared from a methicillin-resistant strain of S. aureus. Occasional mecA- positive isolates were detected among several staphylococcal species. On the other hand, each one of the 134 isolates of Staphylococcus sciuri, a species considered taxonomically the most primitive among staphylococci and found primarily on rodents and primitive mammals, gave positive reaction with the DNA probe when tested under conditions of high stringency. About two thirds (99) of these isolates, all of which belonged to S. sciuri subspecies "sciuri," as well as 9 of the 11 species carnaticum isolates, showed only marginal, if any, resistance to methicillin (minimal inhibitory concentration of 0.75-6.0 micrograms/ml), while most of the remaining isolates that belonged to the subspecies "rodentius" (13 isolates in all) expressed antibiotic resistance with a heterogeneous phenotype similar to those seen in many methicillin-resistance strains of S. aureus In SmaI digests of chromosomal DNA isolated from such "methicillin-resistant S. aureus-like" strains, the mecA probe hybridized with DNA fragments in the range of 145-180 kb, while in subspecies "sciuri" and carnaticum isolates the mecA hybridizing fragment was located in the SmaI fragment with the highest molecular size (> or = 400 kb). A DNA probe comprising an internal sequence to the regulatory gene mecI from Staphylococcus epidermidis identified the presence of sequences with low degree of homology in isolates of the three S. sciuri subspecies. The mecA-reacting sequences in these bacteria differed from mecA of S. aureus in several respects (e.g., by the absence of a ClaI restriction site from mecA of subspecies "sciuri" and carnaticum, and in some isolates of subspecies "rodentius." The uniform presence of mecA in each one of a large number of S. sciuri strains belonging to distinct ribotypes and macrorestriction patterns and recovered over a 20-year period from a wide variety of animal sources and geographic sites suggests that mecA may be a native genetic element with an as yet unidentified physiologic function in this staphylococcal species.
为了探究金黄色葡萄球菌中耐甲氧西林遗传决定因素的起源和/或储存库，我们使用从一株耐甲氧西林金黄色葡萄球菌制备的该基因内部DNA探针，检测了代表葡萄球菌属内13个不同物种的200多株菌株中mecA基因的存在情况。在几种葡萄球菌物种中偶尔检测到mecA阳性分离株。另一方面，松鼠葡萄球菌的134株分离株中的每一株，该物种在分类学上被认为是葡萄球菌中最原始的，主要在啮齿动物和原始哺乳动物身上发现，在高严谨度条件下检测时，与DNA探针呈阳性反应。这些分离株中约三分之二（99株），均属于松鼠葡萄球菌亚种“sciuri”，以及11株康乃馨亚种分离株中的9株，对甲氧西林仅表现出微弱的耐药性（最低抑菌浓度为0.75 - 6.0微克/毫升），而其余大多数属于“啮齿动物亚种”的分离株（总共13株）表现出与许多耐甲氧西林金黄色葡萄球菌菌株相似的异质性耐药表型。在从这种“耐甲氧西林金黄色葡萄球菌样”菌株分离的染色体DNA的SmaI酶切片段中，mecA探针与145 - 180 kb范围内的DNA片段杂交，而在“sciuri”亚种和康乃馨亚种分离株中，mecA杂交片段位于分子大小最高（≥400 kb）的SmaI片段中。一个包含表皮葡萄球菌调节基因mecI内部序列的DNA探针，在三个松鼠葡萄球菌亚种的分离株中鉴定出了低同源性序列的存在。这些细菌中与mecA反应的序列在几个方面与金黄色葡萄球菌的mecA不同（例如，“sciuri”亚种和康乃馨亚种的mecA中没有ClaI限制位点，在“啮齿动物亚种”的一些分离株中也是如此）。在20年期间从广泛的动物来源和地理地点分离得到的大量属于不同核糖体分型和宏观限制模式的松鼠葡萄球菌菌株中，每一株都一致存在mecA，这表明mecA可能是该葡萄球菌物种中一种尚未确定生理功能的天然遗传元件。
