Charles I G, Harford S, Brookfield J F, Shaw W V
J Bacteriol. 1985 Oct;164(1):114-22. doi: 10.1128/jb.164.1.114-122.1985.
Proteus mirabilis PM13 is a well-characterized chloramphenicol-sensitive isolate which spontaneously gives rise to resistant colonies on solid media containing chloramphenicol (50 micrograms ml-1) at a plating efficiency of 10(-4) to 10(-5). Such chloramphenicol-resistant colonies exhibit a novel phenotype with respect to chloramphenicol resistance. When a single colony grown on chloramphenicol agar is transferred to liquid medium and grown in the absence of antibiotic for 150 generations, a population of predominantly sensitive cells arises. This mutation-reversion phenomenon has been observed in other Proteus species and Providencia strains, wherein resistance has been shown to be mediated in each case by the enzyme chloramphenicol acetyltransferase. The cat gene responsible for the phenomenon is chromosomal and can be cloned from P. mirabilis PM13 with DNA prepared from cells grown in the absence or the presence of chloramphenicol. Recombinant plasmids which confer resistance to chloramphenicol carry an 8.5-kilobase PstI fragment irrespective of the source of host DNA. The location of the cat gene within the PstI fragment was determined by Southern blotting with a cat consensus oligonucleotide corresponding to the expected amino acid sequence of the active site region of chloramphenicol acetyltransferase, and the direction of transcription was deduced from homology with the type I cat variant.
奇异变形杆菌PM13是一种特性明确的对氯霉素敏感的菌株，在含有氯霉素（50微克/毫升）的固体培养基上，它会以10⁻⁴至10⁻⁵的平板接种效率自发产生抗性菌落。这些氯霉素抗性菌落表现出一种关于氯霉素抗性的新表型。当在氯霉素琼脂上生长的单个菌落转移到液体培养基中，并在无抗生素的情况下培养150代时，会出现主要为敏感细胞的群体。这种突变 - 回复现象在其他变形杆菌属物种和普罗威登斯菌属菌株中也有观察到，其中抗性在每种情况下都已证明是由氯霉素乙酰转移酶介导的。负责这种现象的cat基因是染色体基因，可以用从在有无氯霉素条件下生长的细胞中制备的DNA从奇异变形杆菌PM13中克隆出来。赋予氯霉素抗性的重组质粒携带一个8.5千碱基对的PstI片段，与宿主DNA的来源无关。通过用与氯霉素乙酰转移酶活性位点区域预期氨基酸序列相对应的cat共有寡核苷酸进行Southern印迹分析，确定了cat基因在PstI片段中的位置，并根据与I型cat变体的同源性推断出转录方向。
