Tait S, Amyes S G
Department of Medical Microbiology, University of Edinburgh Medical School, Scotland.
Epidemiol Infect. 1994 Oct;113(2):247-58. doi: 10.1017/s0950268800051670.
A high incidence of resistance to trimethoprim has been shown in the normal faecal flora in a population in south India. The dihydrofolate reductase (dhfr) genes mediating transferable resistance to trimethoprim have been identified. Unusually, in this study, the dhfrV was shown to be the predominant resistance gene (dhfrV 50% of transconjugants, dhfrIa 30%), the dhfrIb was also detected being distinguished from the dhfrV by an oligo-probe. However, when non-transferable resistance was considered, the dhfrIa was the most prevalent of the dhfrs identified. All those plasmids harbouring the dhfrIa were shown to possess Tn7. All the plasmids that probed positive for the dhfrV and the dhfrIb were shown to be associated with the integrase of the Tn21-like transposons, but 8 of the dhfrV genes were not associated with the Tn21 resolvase. The dhfrIV was shown to be present in all seven plasmids that produced low level trimethoprim-resistance. The dhfrV, first characterized in Sri Lanka, would seem to have a local distribution in this region of Asia but is distinguishable from the dhfrIb only by the use of an oligo-probe.
在印度南部人群的正常粪便菌群中，已显示出对甲氧苄啶的高耐药率。介导对甲氧苄啶可转移耐药性的二氢叶酸还原酶（dhfr）基因已被鉴定。在本研究中不同寻常的是，dhfrV被证明是主要的耐药基因（dhfrV占转接合子的50%，dhfrIa占30%），还检测到了dhfrIb，它可通过寡核苷酸探针与dhfrV区分开来。然而，当考虑非可转移耐药性时，dhfrIa是所鉴定的dhfr中最普遍的。所有携带dhfrIa的质粒都显示含有Tn7。所有对dhfrV和dhfrIb检测呈阳性的质粒都显示与Tn21样转座子的整合酶相关，但8个dhfrV基因与Tn21解离酶无关。dhfrIV在所有产生低水平甲氧苄啶耐药性的7个质粒中均被显示存在。dhfrV最初在斯里兰卡被鉴定，似乎在亚洲这个地区有局部分布，但仅通过使用寡核苷酸探针才能与dhfrIb区分开来。
