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口腔血链球菌是牙周主要有益菌。质粒是细菌染色体外辅助性遗传物质，可以赋予细菌不同表型。本研究目的是检测血链球菌质粒ＤＮＡ存在情况，鉴定其分子大小，初步了解血链菌质粒与耐药性的关系，为今后更深入地在分子水平研究血链菌奠定实验基础。采用碱裂解法小量、快速提取７株血链球菌质粒，λＤＮＡ／ＨｉｎｄⅢ为分子量标准，用琼脂糖凝胶电泳法分离并确定分子大小；采用纸片法测定７株血链菌对链霉素、红霉素、氯霉素、四环素等４种抗生素的耐药性。结果表明，７株血链菌中有４株存在质粒，其分子大小相同，均为２３ｋｂ。血链菌质粒与耐药性之间未发现直接联系。
Streptococcus sanguineus is the main periodontal beneficial bacteria. Plasmids are bacterial extrachromosomal genetic material that can confer different phenotypes on bacteria. The purpose of this study is to detect the presence of Streptococcus sobrinus plasmid DNA, to identify its molecular size, preliminary understanding of the relationship between Streptococcus sobrinus plasmid and drug resistance, and lay the experimental foundation for the further study of Streptococcus sobrinus at the molecular level in the future. Seven strains of Streptococcus sanguis were extracted with a small amount of alkaline lysis, and λDNA / Hind Ⅲ was used as the molecular weight standard. The molecular size was determined by agarose gel electrophoresis. Seven Streptomyces streptozotocin , Erythromycin, chloramphenicol, tetracycline and other four kinds of antibiotic resistance. The results showed that there were 4 plasmids in 7 strains of Streptococcus so the molecular size was the same, both of which were 23kb. No direct correlation was found between Streptococcus sobrinus and drug resistance.