Detection Of Drug Resistance In Streptococcus Suis And Influence Of Chinese Herbs On Its Resistance

Drug resistant isolates of Streptococcus suis (S.suis) are distributed all over the world and the resisitance rate increases day by day, which has resulted in much difficulty to prevent and treat this disease using antibiotics in clinical conditions because of drug resistance. Therefore, people have paid much attention to monitoring, analysing the mechanism, and ovecoming its drug resistance. It has been reported that Chinese herbs have bacteriostatic or bactericidal effects. Some herbs can inhibit the outflow pump system of bacteria, and some herbs can eliminate resistant plasmids of bacteria. In this study, the detection and molecular mechanism of drug resistance in S.suis from different pig farms in Changchun were conducted and the biological influence of Chinese Herbs on its resistance was studied.The drug resistance was detected in S.suis isolated from Changchun by the methods of disk diffusion, double-disk diffusion, and microdilution. The results showed that all the isolates were not resistant to B-acidamide, 5% of them showed low level of resistance to rifampin, 86%-100% of them showed high level of resistance to quinolones, chloramphenicol, tetracycline, and macrolide-Iincosamide-streptomycin B (MLSB). Most of the isolates were multiple drug resistant (MDR). Ninety percent of all the isolates were resistant to MLSB, and 95% of MLSB phenotypes were constitutively MLS resistant (CR). By statistical analysis, MIC50 and MIC90 of other five antibiotics besides (3-acidamide focused mainly on high level of resistance area(128g/ml).The ermB genes of all the isolates were amplified by PCR with the genomic and plasmid DNA as the templates. Results of ligation and sequence analysis showed that difference existed in the different strains. Compared with the sequence of Streptococcus pneumonia and Enterococcus faecalis etc. in Genebank, there was over 98% homology. Those datamanifested that MLSB resistance of S.suis isolates in Changchun resulted mainly from ermB gene which was of different origins. It is possible that ermB gene exchanged between the bacteria from human and animal.Nine herbs which showed high or middle susceptible activity to resistant S.suis were screened using the routine methods. The herb V had the lowest MIC (16 mg/ml) compared to the other twentiy-nine herbs and there was no synergistic action between the herbs and antibiotics. After the resistant strains were treated for 16-72h with the herbs which was under two-time-dilution of MICs, the MIC of MLSB maintained at 4-32g/ml within 6-12h, but recovered the initial level (128-256g/ml) after 16h. These results showed that some herbs are obviously bacteriostatic to resistant S.suis strains, and the susceptibility of the resistant strains to MLSB is associated with the time of herb treatment.