| The Streptococcicosis is the infectious disease of different types of clinical diagnosis which causes by many different groups of Streptococcus. Streptococcus suis could cause meningitis, arthritis, pneumonia, endocarditis, multiple serositis and local abscess and so on, it could also infect and be lethal to the human. It is one kind of important pathogeny of human and livestock. With the wide application of antibiotics at home and abroad, the resistance of streptococcus suis is quite serious, and presents some regional characteristics. So in the specific process of treatment, only understand the local features of drug-resistant strains and choose sensitivity drug, can obtain good therapeutic effect. The resistance of Streptococcus suis to tetracycline is increasingly serious, with which as the main effective drugs are widely used. Therefore, this experiment through the research of resistance and resistance genes at the molecular level to tetracycline, strived to provide the basis for clarifying the resistant mechanism of Streptococcus suis to tetracycline. The establishment of multiplex PCR for detection of resistant genes, made it possible to detect the resistance of Streptococcus suis to tetracycline. The aspects of the study were as follows:1. Detected the resistance of Streptococcus suis to antibiotics in different regions. Detected the resistance of 106 Streptococcus suis identified in different regions to cefepime, ceftriaxone, erythromycin, clarithromycin, levofloxacin, ofloxacin, clindamycin, tetracycline, vancomycin and chloromycetin through susceptibility test. The resistant rate of tested strains to tetracylin was 100 %; to ceftriaxone, erythromycin, clarithromycin, clindamycin there was certain resistance, and the resistant rate was 15 %~20 %. The strains kept good sensitivity to cefepime, vancomycin and chloromycetin. Multiple resistant rate was 33 %, and multiple drug-resistant phenomenon was mainly 2 multiple (17 strains, 16.1 %). Main drug-resistant strains and multiple drug-resistant strains mostly appeared in Jiangsu, Sichuan and Chongqing. This experiment provided the basis to master the resistance of Streptococcus suis in most regions of China and to find effective clinical antibiotics for treatment. 2. Provided the basis to research the resistant mechanism of Streptococcus suis to tetracycline at the molecular level. The strains were examined for their resistance to tetracycline by broth dilution method. Antibiotic resistance genes of tet(M),tet(O),tet(K),tet(L),tet(Q),tet(S),tet(T) and tet(W) were amplified by PCR, sequenced and compared. More than 99 % of the tested strains were height resistant ones, and in most regions of China the resistant phenomenon of Streptococcus suis were serious. The resistant genes of tet (M) (80.2 %), tet (O) (18.9 %) and tet (L) (14.2 %) detected in the experiment showed that the resistant mechanism of Streptococcus suis to tetracycline was mainly composed of tet (M) gene mediated ribosomes protection in our nation. Meanwhile the results showed that when tet (M), tet (O) genes existed alone, the resistance of the strains which contained tet (M) was higher than the latter ones'. Nucleotide sequence comparison showed the tet(M) and the tet(O) genes were highly identical to the published sequences(95 %~100 %, 95 %~99 %, which showed that there was a wide spread of tet gene between the same and different species of bacteria. This experiment provided the basis of the resistant mechanism of Streptococcus suis to tetracycline.3. Established multiplex PCR for detection of resistant genes Successfully. After analyzing the sequence of resistant gene tet(M) and tet(O), designed 3 pairs of specific primer in its highly conservative district and established multiplex PCR for detection of resistant genes. Applicated this method to detect the resistance of 15 strains to tetracycline, and comparied The results with susceptibility test. The results showed that this method was sensitive, specific and repeatability, and the similar rate of the two method was100 %.
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