Sundström L, Vinayagamoorthy T, Sköld O
Antimicrob Agents Chemother. 1987 Jan;31(1):60-6. doi: 10.1128/AAC.31.1.60.
A novel trait for transferable resistance to high concentrations of trimethoprim was found to dominate among enterobacteria collected from different parts of Sri Lanka. Drug resistance was a result of the production of dihydrofolate reductase with a decreased sensitivity to antifolates. By characterization of the partially purified enzyme and by restriction enzyme digestion analysis, the newly found gene was shown to be distinct from the earlier known plasmid-borne resistance genes which express dihydrofolate reductases of types I, II, and III. Cloning of fragments containing the resistance gene and further restriction enzyme digestion analysis showed that this gene was inserted very close to a sulfonamide resistance gene. Evolution of trimethoprim resistance in Sri Lanka thus seems to have taken a different route from that taken in the industrialized world, where transposon Tn7 seems to dominate. The close combination of the new trimethoprim resistance gene with sulfonamide resistance on the plasmids studied would effect an efficient spread of these genes, since trimethoprim has most often been used in combination with a sulfonamide.
在从斯里兰卡不同地区收集的肠杆菌中，发现一种对高浓度甲氧苄啶具有可转移抗性的新特性占主导地位。耐药性是由于产生了对抗叶酸药物敏感性降低的二氢叶酸还原酶。通过对部分纯化酶的特性分析以及限制性内切酶消化分析，表明新发现的基因与早期已知的表达I型、II型和III型二氢叶酸还原酶的质粒介导耐药基因不同。对含有耐药基因的片段进行克隆并进一步进行限制性内切酶消化分析表明，该基因插入位置非常靠近一个磺胺耐药基因。因此，斯里兰卡甲氧苄啶耐药性的演变似乎与工业化国家不同，在工业化国家转座子Tn7似乎占主导地位。在所研究的质粒上，新的甲氧苄啶耐药基因与磺胺耐药性紧密结合，这将导致这些基因的有效传播，因为甲氧苄啶最常与磺胺类药物联合使用。
