一株磺胺二甲嘧啶抗性菌的筛选及抗性机制研究

为研究地下水中磺胺类抗性菌的抗性特征与抗性机制，在调研北京市东南发展区地下水受抗生素污染情况基础上，从中筛得一株磺胺二甲嘧啶（SMZ）抗性菌SMZ-R9，经形态学观察、生理生化试验及16S rRNA基因测序分析，鉴定为乳酸不动杆菌（Acinetobacter lactucae）.使用荧光定量PCR与普通PCR定量以及定性检测抗性基因（ARGs），发现菌株SMZ-R9同时携带3种磺胺ARGs（sul1、sul2、sul3）、1种甲氧苄啶ARGs（dfrA1）以及Int1基因；通过对基因序列进行同源性比对及KEGG功能注释，发现sul2、dfrA1基因为编码二氢蝶呤合成酶（DHPs）与二氢叶酸还原酶（DHFR）的核酸序列，表达产物分别催化叶酸合成的上游与下游途径，共同介导菌株SMZ-R9的SAs抗性.可见，通过对ARGs编码蛋白的功能注释与分析，可为微生物的抗生素抗性机制在基因水平的研究提供理论依据. 

Screening and Resistance Mechanism of Sulfamethazine-Resistant Strain

In order to study the resistance characteristics and mechanism of sulfanilamide resistant bacteria in groundwater, this paper screened a sulfamethazine (SMZ) resistant strain SMZ-R9 based on the investigation of groundwater contaminated by antibiotics in the southeast development area of Beijing, which was identified as Acinetobacter lactucae by morphological observation, physiological and biochemical experiments and 16S rRNA gene sequencing analysis. Then the resistance genes (ARGs) were detected quantitatively and qualitatively by fluorescence quantitative PCR and conventional PCR, and it was found that SMZ-R9 carried three sulfanilamide ARGs (sul1, sul2, sul3), one trimethoprim ARGs (dfrA1) and Int1 genes. By homology comparison and KEGG functional annotation, it was found that sul2 and dfrA1 genes were the nucleic acid sequences encoding dihydrotrexate synthase (DHPs) and dihydrofolate reductase (DHFR). The expression products catalyzed the upstream and downstream pathways of folate synthesis, respectively, and jointly mediated the SAs resistance of SMZ-R9. In conclusion, the functional annotation and analysis of ARGs-encoded proteins can provide a theoretical basis for the study of antibiotic resistance mechanisms of microorganisms at the gene level.