LeBlanc D J, Lee L N
J Bacteriol. 1982 May;150(2):835-43. doi: 10.1128/jb.150.2.835-843.1982.
Streptococcus faecalis strain JH1 harbors two conjugative plasmids: pJH1, an R plasmid mediating resistance to kanamycin, streptomycin, gentamicin, erythromycin, and tetracycline, and pJH2, a hemolysin-bacteriocin plasmid. Studies of plasmid-cured derivatives of strain JH1 and of transconjugates obtained after mixed incubation of JH1 with the plasmid-free S. faecalis strain JH2-2 revealed the presence of two tetracycline resistance determinants in strain JH1. One determinant mediated constitutive resistance to 40 micrograms of tetracycline per ml and was associated with plasmid pJH1. The second determinant, either on the chromosome of strain JH1 or on an undetectable plasmid, was inducible by tetracycline and enabled the host strain, in the absence of pJH1, to grow in the presence of 80 micrograms of tetracycline per ml. One transconjugant, strain DL172, was resistant to 80 micrograms of tetracycline per ml, sensitive to kanamycin, streptomycin, and erythromycin, and hemolytic in the presence, but not in the absence, of tetracycline. A single plasmid, pDL172, from this strain consisted of plasmid pJH2 and a 17.8-kilobase segment of DNA homologous to total cell DNA from strain JH1 but did not contain plasmid pJH1. Whether the addition of heterologous DNA to plasmid pJH2 occurred by translocation of a 17.8-kilobase tetracycline resistance transposon or by classical recombination with pJH2 has not been determined.
粪肠球菌JH1菌株含有两种接合质粒：pJH1，一种R质粒，介导对卡那霉素、链霉素、庆大霉素、红霉素和四环素的抗性；以及pJH2，一种溶血素-细菌素质粒。对JH1菌株的质粒消除衍生物以及JH1与无质粒的粪肠球菌菌株JH2-2混合培养后获得的转接合子的研究表明，JH1菌株中存在两个四环素抗性决定簇。一个决定簇介导对每毫升40微克四环素的组成型抗性，并且与质粒pJH1相关。第二个决定簇，要么在JH1菌株的染色体上，要么在一个无法检测到的质粒上，可被四环素诱导，并且在没有pJH1的情况下，使宿主菌株能够在每毫升80微克四环素的存在下生长。一个转接合子，DL172菌株，对每毫升80微克四环素具有抗性，对卡那霉素、链霉素和红霉素敏感，并且在有四环素存在时溶血，但在没有四环素时不溶血。来自该菌株的单个质粒pDL172由质粒pJH2和与JH1菌株的总细胞DNA同源的17.8千碱基DNA片段组成，但不包含质粒pJH1。向质粒pJH2中添加异源DNA是通过17.8千碱基四环素抗性转座子的易位还是通过与pJH2的经典重组发生，尚未确定。
