Genetic studies of kanamycin resistance in Campylobacter jejuni

Campylobacter jejuni 3H40 and 4B20 harbored 59-kilobase (kb) self-transmissible plasmids encoding resistance to kanamycin and tetracycline. Although the two antibiotic resistances were more frequently inherited together, some transconjugants and ethidium bromide segregants which were resistant to only one of these antibiotics were recovered. The kanamycin-susceptible, tetracycline-resistant segregants carried plasmids 4 kb smaller than the 59-kb plasmids of their parents, whereas the kanamycin-resistant, tetracycline-susceptible segregants contained no detectable plasmid DNA. Restriction endonuclease maps of deleted forms of the 59-kb plasmids revealed that deletions and rearrangements of 4-kb lengths of DNA were associated with loss of kanamycin resistance. Translocation of the kanamycin resistance determinant between plasmid and chromosomal DNA was demonstrated. Such phenomena have not been previously described in C. jejuni spp. and are consistent with the interpretation that the kanamycin resistance determinant is encoded by a translocatable element.