Preparation and primary application of antiserum to aminoacy1-3″-adenylyltransferase in integron / 中华检验医学杂志

ABSTRACT

ObjectiveTo 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.MethodsaadA2 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.ResultsRecombined 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.