Jacob A E, Hobbs S J
J Bacteriol. 1974 Feb;117(2):360-72. doi: 10.1128/jb.117.2.360-372.1974.
A strain of Streptococcus faecalis var. zymogenes, designated JH1, had high-level resistance to the antibiotics streptomycin, kanamycin, neomycin, erythromycin, and tetracycline. These resistances were lost en bloc from approximately 0.1% of cells grown in nutrient broth at 45 C. The frequency of resistance loss was not increased by growth in the presence of the "curing" agents acriflavine or acridine orange, but after prolonged storage in nutrient agar 17% of cells became antibiotic sensitive. Covalently closed circular deoxyribonucleic acid (DNA) molecules were isolated from the parental strain and from antibiotic-sensitive segregants by using cesium chloride-ethidium bromide gradients. DNA molecular species were identified by using neutral sucrose gradients. Strain JH1 contained two covalently closed circular DNA species of molecular weights 50 x 10(6) and 38 x 10(6). An antibiotic-sensitive segregant, strain JH1-9, had lost the larger molecular species. A second sensitive segregant, strain JH1-5, had also lost the larger molecular species but a new molecular species of approximate molecular weight 6 x 10(6) was present. The antibiotic resistances that were curable from the parental strain were transferred to antibiotic-sensitive strains of S. faecalis and to strain JH1-9, during mixed incubation in nutrient broth at 37 C. Data to be described are interpreted to suggest that the transfer is by a conjugal mechanism. Analysis of the plasmid species in recipient clones showed that all had received the plasmid of molecular weight 50 x 10(6). Strain JH1-5 was not a good recipient. Analysis of one successful recipient clone of JH1-5 revealed that it had gained the 50 x 10(6) molecular weight plasmid but lost the 6 x 10(6) molecular weight species. These data are interpreted to mean that the multiple antibiotic resistance is borne by a transferable plasmid of 50 x 10(6) molecular weight, and that in clone JH1-5 this plasmid suffered a large deletion leaving only a 6 x 10(6) remnant which was incompatible with the complete replicon.
一种粪肠球菌发酵变种，命名为JH1，对链霉素、卡那霉素、新霉素、红霉素和四环素具有高水平抗性。在45℃的营养肉汤中生长的约0.1%的细胞中，这些抗性会整体丧失。在吖啶黄素或吖啶橙等“治愈”剂存在的情况下生长，抗性丧失的频率并未增加，但在营养琼脂中长时间储存后，17%的细胞变得对抗生素敏感。通过使用氯化铯-溴化乙锭梯度从亲代菌株和抗生素敏感分离株中分离出共价闭合环状脱氧核糖核酸（DNA）分子。通过使用中性蔗糖梯度鉴定DNA分子种类。菌株JH1含有两种分子量分别为50×10⁶和38×10⁶的共价闭合环状DNA种类。一种抗生素敏感分离株JH1-9失去了较大的分子种类。另一种敏感分离株JH1-5也失去了较大的分子种类，但出现了一种分子量约为6×10⁶的新分子种类。在37℃的营养肉汤中混合培养期间，亲代菌株中可治愈的抗生素抗性被转移到粪肠球菌的抗生素敏感菌株和菌株JH1-9中。待描述的数据被解释为表明这种转移是通过接合机制进行的。对受体克隆中的质粒种类分析表明，所有克隆都获得了分子量为50×10⁶的质粒。菌株JH1-5不是一个好的受体。对JH1-5的一个成功受体克隆的分析表明，它获得了分子量为50×10⁶的质粒，但失去了分子量为6×10⁶的种类。这些数据被解释为意味着多重抗生素抗性由一个分子量为50×10⁶的可转移质粒携带，并且在克隆JH1-5中，该质粒发生了大的缺失，仅留下一个6×10⁶的残余物，它与完整的复制子不相容。
