Dubin D T, Chikramane S G, Inglis B, Matthews P R, Stewart P R
Department of Molecular Genetics and Microbiology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway 08854.
J Gen Microbiol. 1992 Jan;138(1):169-80. doi: 10.1099/00221287-138-1-169.
Methicillin-resistant (Mcr) staphylococci contain chromosomal DNA that is absent from Mcs cells. This extra DNA harbours the methicillin resistance determinant mec and often other resistance determinants. The mec region can differ substantially in structure among different isolates. We present studies on the mec region of a group of Staphylococcus aureus isolates prevalent in Australia and London. Southern hybridization analyses of a prototype Australian isolate, ANS46, and an isogenic Mcs deletion mutant, ANS62, allowed the physical map of the region to be extended to 55 kb. The DNA corresponding to the deletion, which includes mec and resistance determinants for mercury, cadmium (Cd) and tetracycline, amounted to 41 kb. It was bounded precisely at one end by the macrolides-lincosamides-streptogramin B (MLS)-resistance transposon, Tn554. Near the other end was an element with homology to Tn554, psi Tn554, which carried the Cdr determinant. The mec region of an American Mcr isolate, R35, was found to be virtually the same as that of ANS46, except that it lacked Tn554. Another class of American Mcr isolates, prevalent since 1987, differs markedly from ANS46 in mec region organization. However, this other American class also contains an insertion of Tn554 in the mec region, and the attachment site for this insertion was found to have significant homology to attachment sites for the Tn554 and psi Tn554 insertions in the mec region of the Australian strain. These results suggest possible roles of Tn554 and Tn554-like elements in the evolutionary variation of the mec region.
耐甲氧西林（Mcr）葡萄球菌含有Mcs细胞所没有的染色体DNA。这段额外的DNA携带了甲氧西林耐药决定簇mec，并且常常还带有其他耐药决定簇。不同菌株之间，mec区域的结构可能有很大差异。我们对一组在澳大利亚和伦敦流行的金黄色葡萄球菌菌株的mec区域进行了研究。对一株典型的澳大利亚菌株ANS46及其同基因Mcs缺失突变体ANS62进行的Southern杂交分析，使该区域的物理图谱扩展到了55 kb。与缺失相对应的DNA，包括mec以及汞、镉（Cd）和四环素的耐药决定簇，共计41 kb。其一端精确地以大环内酯类-林可酰胺类-链阳菌素B（MLS）耐药转座子Tn554为界。另一端附近是一个与Tn554有同源性的元件psi Tn554，它携带了Cdr决定簇。发现一株美国Mcr菌株R35的mec区域与ANS46的几乎相同，只是缺少Tn554。另一类自1987年以来流行的美国Mcr菌株，其mec区域组织与ANS46明显不同。然而，这另一类美国菌株在mec区域也有Tn554的插入，并且发现该插入的附着位点与澳大利亚菌株mec区域中Tn554和psi Tn554插入的附着位点有显著同源性。这些结果提示了Tn554和Tn554样元件在mec区域进化变异中的可能作用。
