Heaton M P, Handwerger S
Laboratory of Microbiology, Rockefeller University, New York, New York 10021, USA.
Microb Drug Resist. 1995 Summer;1(2):177-83. doi: 10.1089/mdr.1995.1.177.
Recent epidemiological evidence suggests that horizontal gene transfer may be an important mechanism for dissemination of vancomycin resistance. A filter mating survey of 21 VanA Enterococcus faecium isolates from The New York Hospital showed that 14 of these isolates transferred vancomycin resistance (Vmr) to the plasmid-free reference strain Enterococcus faecalis JH2-2. One isolate, E. faecium R7, was selected for further study based on its ability to transfer Vmr to strain JH2-2 in liquid culture. Analysis of the plasmid content of transconjugants revealed three general classes. The predominant class (28 of 47 transconjugants) contained two separate plasmids: pHKK702 and pHKK703. pHKK702 is a 41-kb plasmid that contains an element indistinguishable from the Vmr transposon Tn1546 and an element that hybridizes with an ermB probe from the Staphylococcus aureus erythromycin resistance transposon Tn551. pHKK703 is a 55-kb plasmid that hybridizes with probes for the sex pheromone response genes prgA, prgB, and prgX derived from the E. faecalis plasmid pCF10. The second group of transconjugants (18 of 47) contained various recombinant forms of pHKK702 and pHKK703, whereas a third transconjugant class contained only pHKK702 (1 of 47). Transconjugants that contained both pHKK702 and pHKK703 were able to efficiently transfer Vmr to recipient strains in broth or on filters. However, no transfer of Vmr was detected using the donor containing only pHKK702. The transfer of Vmr from the recombination-deficient derivative of E. faecalis JH2-2 [strain UV202(pHKK702, pHKK703)] was reduced 600-fold compared to that of JH2-2(pHKK702, pHKK703). We propose that pHKK703 functions as an E. faecium sex pheromone response plasmid that conjugatively mobilizes pHKK702, and that a major pathway for this mobilization may require donor-mediated recombination proficiency. This report provides the first example in which a plasmid containing a Tn1546-related element is conjugatively mobilized.
近期的流行病学证据表明，水平基因转移可能是万古霉素耐药性传播的一个重要机制。对纽约医院分离出的21株VanA粪肠球菌进行的滤膜交配试验表明，其中14株分离株将万古霉素耐药性（Vmr）转移至无质粒的参考菌株粪肠球菌JH2-2。基于其在液体培养中能够将Vmr转移至菌株JH2-2的能力，选择了一株分离株，即粪肠球菌R7进行进一步研究。对转接合子的质粒含量分析揭示出三种一般类型。主要类型（47个转接合子中的28个）含有两个独立的质粒：pHKK702和pHKK703。pHKK702是一个41 kb的质粒，含有一个与Vmr转座子Tn1546无法区分的元件以及一个与来自金黄色葡萄球菌红霉素耐药转座子Tn551的ermB探针杂交的元件。pHKK703是一个55 kb的质粒，与源自粪肠球菌质粒pCF10的性信息素反应基因prgA、prgB和prgX的探针杂交。第二组转接合子（47个中的18个）含有pHKK702和pHKK703的各种重组形式，而第三类转接合子仅含有pHKK702（47个中的1个）。同时含有pHKK702和pHKK703的转接合子能够在肉汤或滤膜上有效地将Vmr转移至受体菌株。然而，使用仅含有pHKK702的供体未检测到Vmr的转移。与JH2-2(pHKK702, pHKK703)相比，来自粪肠球菌JH2-2的重组缺陷衍生物[菌株UV202(pHKK702, pHKK703)]的Vmr转移减少了600倍。我们提出，pHKK703作为粪肠球菌性信息素反应质粒发挥作用，通过接合作用使pHKK702移动，并且这种移动的主要途径可能需要供体介导的重组能力。本报告提供了含有Tn1546相关元件的质粒通过接合作用移动的首个实例。
