Rashtchian A, Booth S J
J Bacteriol. 1981 Apr;146(1):121-7. doi: 10.1128/jb.146.1.121-127.1981.
A Bacteroides fragilis strain resistant to penicillin G, tetracycline, and clindamycin was screened for the presence of plasmid deoxyribonucleic acid (DNA). Agarose gel electrophoresis of ethanol-precipitated DNA from cleared lysates of this strain revealed two plasmid DNA bands. The molecular weights of the plasmids were estimated by their relative mobility in agarose gel and compared with standard plasmids with known molecular weights. The molecular weights were 3.40 +/- 0.20 x 10(6) and 1.95 +/- 0.05 x 10(6) for plasmids pBY1 and pBY2, respectively. Plasmid DNA purified by cesium chloride-ethidium bromide gradient centrifugation was used to transform a restriction- and modification-negative strain of Escherichia coli. Penicillin G- and tetracycline-resistant transformants were screened for the presence of plasmid DNA. A plasmid band corresponding to a molecular weight of 1.95 x 10(6) was present in all transformants tested. Curing experiments demonstrated that the plasmid, referred to as pBY22 when present in transformants, was responsible for penicillin G and tetracycline resistance. Plasmid pBY22 was mobilized and transferred to other E. coli strains by plasmid R1drd-19. Stability of pBY22 was examined in different E. coli strains and was shown to be stably maintained in both restriction-negative and restriction-positive strains. Unexpectedly, pBY2 and pBY22 were resistant to digestion by 12 different restriction endonucleases.
筛选了一株对青霉素G、四环素和克林霉素耐药的脆弱拟杆菌菌株，以检测其是否存在质粒脱氧核糖核酸（DNA）。对该菌株澄清裂解物中乙醇沉淀的DNA进行琼脂糖凝胶电泳，结果显示有两条质粒DNA条带。通过质粒在琼脂糖凝胶中的相对迁移率估算其分子量，并与已知分子量的标准质粒进行比较。质粒pBY1和pBY2的分子量分别为3.40±0.20×10⁶和1.95±0.05×10⁶。通过氯化铯-溴化乙锭梯度离心纯化的质粒DNA用于转化一株限制修饰阴性的大肠杆菌菌株。筛选对青霉素G和四环素耐药的转化子，检测其是否存在质粒DNA。在所有测试的转化子中均出现了一条分子量为1.95×10⁶的质粒条带。消除实验表明，该质粒（在转化子中称为pBY22）赋予了对青霉素G和四环素的耐药性。质粒pBY22通过质粒R1drd-19被转移到其他大肠杆菌菌株中。在不同的大肠杆菌菌株中检测了pBY22的稳定性，结果表明它在限制阴性和限制阳性菌株中均能稳定维持。出乎意料的是，pBY2和pBY22对12种不同的限制性内切酶具有抗性。
