Isolating And Identification Of Plasmid Coding Streptomycin Resistance From The Avian Escherichia Coli And Epidemiology Of The Drug Resistant Genes

I have gained one plasmids which coding streptomycin resistance through the convert experiment. Drug sensitivity tests were done to verify the transformant gained Streptmycin resistance .and PCR experiment shows that this R plasmid phore aadA1 gene onjy. Sequencing result finds that sequence of the aadA1 gene in the Rplasmid shares more than 98.2% homology with the gene aadA1 signed in GenBank .The data come up to 100% when it is translated into aa sequence.Gene coding streptomycin resistance such as aadA1,strA,strB were amplified by pojymerase chain reaction (PCR) from Avian Escherichia coli isolated from sick poultry. The primers were designed according to the sequence of aadA1,StrA,StrB gene published in GenBank . It intrests me that some strains which contain the Sr gene are sensitive to streptomycin.I suppose it is because the Sr gene have been mutanted or they exist as one intron in the chromatosome. Probabjy these strains will be turned into ones resistant to the Streptmycin not long after. Sequent result and homology anajyses prove that these three kinds of Sr gene share more than 98% homology with the sequence cited from GenBank. The percentage of aadA1 gene is 98.2%,pet of strA is 99.8%,strB is 99.9%.Wha's noteworthy is that the strB gene in the AC3 and AD5 strain are both inserted with one piece of sequence (GTTTCGC). .Most inportant of all, there exists more than one terminator following the inserted sequence. It is possibly one new reason why the Sr gene strB can not encode toinactive enzyme.