摘要目的 制备氨基糖苷-3″-腺苷酰基转移酶[AAD(3″)]特异性抗血清,并探讨其在检测第1类整合子8种不同可变区启动子(PcS、PcH2、PcH1、PcW、PcS-P2、PcH2-P2、PcH1 -P2和PcW-P2)下游基因盒中aadA2基因表达水平的应用价值.方法 用聚合酶链反应(PCR)扩增aadA2基因,并克隆至表达载体pET19b中,诱导表达并纯化带组氨酸标签的重组AAD(3″)蛋白,免疫大耳白兔制备抗AAD(3″)特异性抗血清.以制备的抗AAD(3″)抗血清为一抗,用免疫印迹法(WB)检测不同可变区启动子下游基因盒中aadA2基因的翻译水平,用微量肉汤稀释法检测链霉素对含不同可变区启动子及其下游aadA2基因盒的大肠埃希菌JM109的最低抑菌浓度(MIC).结果 成功构建重组的AAD(3″)蛋白表达质粒pET1 9b-aadA2,经测序确认转化大肠埃希菌BL21( DE3)获得1株高表达可溶性重组AAD(3″)蛋白的工程菌株,发酵后用镍柱纯化获得纯度＞90％的重组AAD(3″)蛋白,免疫大耳白兔获得效价＞ 1∶100 000的抗AAD(3″)特异性抗血清.WB检测8种不同可变区启动子下游aadA2基因翻译产物AAD(3″)蛋白的表达水平,设定启动子PcW下游AAD(3″)蛋白的相对表达水平为1,重复3次测得启动子PcS、PcH2、PcH1、PcS-P2、PcH2 -P2、PcH1-P2及PcW-P2下游AAD(3″)蛋白相对表达水平依次为12.9±2.3、9.1±1.0、2.0±0.4、16.0±1.3、14.1±1.3、10.5±0.7、8.9±1.7,且不同可变区启动子下游AAD(3″)蛋白的相对表达水平差异具有统计学意义(F=32.421,P＜0.01).微量肉汤稀释法重复3次测得链霉素对含启动子PcS、PeH2、PcH1、PcS-P2、PcH2-P2、PcH1 P2、PcW、PcW-P2及其下游aadA2基因重组质粒的大肠杆菌JM109的MIC平均值依次为256、256、64、128、32、128、4、64 mg/L,表明不同可变区启动子下游aadA2基因的表达水平不同可赋予宿主细菌对链霉素产生不同水平的耐药.结论 成功纯化出可溶性重组AAD(3″)蛋白,免疫大耳白兔获得高效价的抗AAD(3″)特异性抗血清,为进一步研究整合子中整合酶基因与可变区基因盒表达之间的相互关系奠定基础.不同可变区启动子下游耐药基因盒的表达水平明显不同,赋予宿主细菌对相应抗菌药物的耐药水平明显不同,因此在对临床菌株进行第1类整合子分子流行病学调查时,应重视可变区启动子分类方面的研究.

abstractsObjective To prepare antiserum specific to aminoacy1-3″-adenylyltransferase [ AAD (3″) ],and to explore the application value of the prepared antiserum in detecting the expression levels of aadA2 gene that downstream of 8 different promoters (PcS,PcH2,PcH1,PcW,PcS-P2,PcH2-P2,PcH1P2 and PcW-P2 ) of variable regions in class 1 integron.Methods aadA2 gene was amplified by polymerase chain reaction(PCR) and cloned into the expression plasmid pET19b.After inducing,the recombined aminoacy1-3″-adenylyltransferase[ AAD(3″)] with His-tag was expressed,purified and immunized rabbits to get anti- AAD(3″) specific serum.The prepared antiserum was used to detect the translation levels of aadA2 gene that downstream of different promoters of variable regions in class 1 integron by Western blotting (WB).Broth microdilution method was used to detect the minimal inhibitory concentrations (MIC) to streptomycin in Escherichia coli JM109 with aadA2 gene downstream of different promoters of variable regions.Results Recombined AAD (3″) expression plasmid pET19b-aadA2 was constructed successfully and was verified by sequence analysis.After transformed into E.coli BL21 ( DE3 ),a resoluble recombined AAD(3″) high expression strain was obtained.After fermentation,recombined AAD(3″) was purified and immunized rabbits.The anti- AAD(3″) specific serum was obtained with titer ＞ 1∶100 000.WB was used to detect the expression levels of AAD (3″),the translation product of aadA2 gene,that downstream of 8 different promoters of variable regions.The relative expression level of AAD (3″) that downstream of PcW was assumed to be 1,then the relative expression levels of AAD(3″),which all were detected 3 times independently,that downstream of PcS,PcH2,PcH1,PcS-P2,PcH2-P2,PcH1-P2 and PcW-P2 were 12.9±2.3,9.1±1.0,2.0±0.4,16.0±1.3,14.1 ±1.3,10.5±0.7 and 8.9 ±1.7 respective.Very different expression levels of AAD (3″) that downstream of different promoters of variable regions were obtained( F =32.421,P ＜ 0.01 ).The mean values of MIC,which all were detected 3 times independently,to streptomycin in E.coli JM109 with aadA2 gene downstream of PcS,PcH2,PcH1,PcW,PcS-P2,PcH2P2,PcH1-P2 and PcW-P2 were 256,256,64,128,32,128,4 and 64 mg/L respective.These results indicated the different expression levels of aadA2 gene that downstream of different promoters of variable regions can confer their host bacteria different resistance levels to streptomycin.Conclusions Resoluble recombined AAD(3″) is purified successfully and high titer anti- AAD(3″) specific antiserum is obtained from the immunized rabbits.This laid foundation for further investigation on the correlationship between the expressions of intI1 gene and the gene cassettes within variable regions.The expression levels of antibiotic gene cassettes that downstream of different promoters of variable regions are very different,so are the very different antibiotic resistance levels of the host bacteria.Therefore more attentions should be paid to the researches on the classification of promoters of variable regions when molecular epidemiology studies on the class 1 integrons in clinical isolates were conducted.