| Staphylococci, Streptococci and Escherichia coli are the main pathogenic bacteria which cause of bovine mastitis, and Staphylococcus epidermidis(Se), thus is considered as opportunistic pathogenic bacteria with low pathogenic ability. So it is proved that it does not cause bovine mastitis disease outbreak. According to our previous studies, we found that Staphylococcus epidermidis biofilm can be formed in mastitis very easily. The biofilm is a repository for drug-resistant Staphylococcus aureus, which causes the increasing multi-drug resistance of bacterial. In recent years researchers have found that bacteria integron subsystem plays an important role in the formation of drug resistance by capturing exogenous genes directly through the integrase, and then becoming drug-resistance gene cassette. The expression of drug-resistant gene will result in multiple drug resistance bacteria. Research on the relationship between drug-resistance and integrons in strains has theoretical and practical value.In the present research, we first analyse drug resistance of Se which isolates from bovine clinical mastitis and integron distribution characteristic by using pharmacological and molecular biology methods, then further study the correlation between integron and drug resistance of Se. The results show that Se which was isolated from clinical resistanted to commonly used antimicrobial, the drug rate was about 16.7%～100%, and Se has multiple antibiotic resistance. And all isolates have highest drug resistance to penicillin. Through research on the bacterial integron existence characteristics we know that the detection rate of class 1 integron was 60%, the detection rate of class 2 integron was 16.7% and class 3 integron was non-existent. The detection rate of class 1 integron in Se which can formation biofilm was 71.4%, and thedetection rate of class 1 integron in Se which can not formation biofilm was 56.5%. And in Se, the resistance rates class 1 integron positive strains greater than negative strains. The results show that the presence of the largest class 1 integron in Se, and the resistance of Se have some relevance; in class 1 integron postitive Se, the gene cassette was 77.8%, and found that each drug gene cassette carrying at least two resistance genes, and aminoglycoside acetyltransferase, dihydrofolate reductase and chloramphenicol acetyltransferase were the most frequently. In Se, gene cassette positive strains resistant species of integronhigher gene cassette negative strains, which the results show that the gene cassette of integron and multi-drug resistant bacteria has a close relationship.The amount of class 1 integrase gene (intI1) expression was further studied deeply in biofilm and planktonic bacteria, and the effect of drugs on intll expression level. The results showed that the clinical strains of Se expressed intll in the state of biofilm and planktonic, in which the expression level in biofilm cells were higher than their planktonic cells. Along with the continuous increasing of biofilm, the expression quantity of intll was rising. The increasing of biofilm density could affect the integron in the frequency of capturing the resistance gene boxes and thus be conducive to the spread of drug resistant genes. Matrine on forming biofilm positive strains had higher than or equal to MIC on that of negative strains, and matrine can inhibit biofilm. intll was down-regulated expressed on mRNA level by matrine in states of biofilm and planktonic cells, and intll was down-regulated the maxium in the state of planktonic cells. Suggesting that matrine could reduce the efficiency of transferring resistant genes by integron and could prevent the bacterial from the formation of drug resistance and the spread function of drug resistant gene. However, the specific mechanisms are still need to be discussed. |
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