Three antibiotic resistance genes, responsible for high-level kanamycin (Km), streptomycin (Sm) and erythromycin (Em) resistance among numerous streptococcal isolates of human and animal origin, may have been disseminated via a common transposon. Streptococcus faecalis strains JH1, LDR175 and LDR517 are all resistant to high levels of Km, Sm and Em. Strain JH1 was isolated from a human clinical patient, strain LDR175 from a healthy chicken, and strain LDR517 was a multiply resistant transconjugant isolate obtained from a mating between strain LDR175 and the plasmid-free recipient strain JH2-2. In strain JH1, the Km, Sm and Em resistance traits are encoded by three distinct genes carried on plasmid pJH1. Each of these genes, cloned from pJH1, hybridized only to chromosomal DNA from strains LDR175 and LDR517. A segment of DNA, greater than kilobase pairs (kbp) in size and carrying all three resistance genes, was transposable to a hemolysin-bacteriocin plasmid, pAD1, when also present in strain LDR517 or a strain harboring pJH1. Preliminary restriction endonuclease maps of the transposed DNA from pJH1 or strain LDR517 appeared identical. Three tetracycline resistance (TcR) genes, tetL, tetM, and tetN, have been identified in the genus Streptococcus. We cloned a fourth TcR gene, tetO, from a strain of Streptococcus mutans. This cloned gene did not hybridize to tetL, tetM or tetN, but did hybridize, under stringent conditions, to TcR plasmids from species of the Gram-negative intestinal pathogen, Campylobacter, and to a cloned TcR gene from a strain of Campylobacter jejuni. The TcR genes from S. mutans and C. jejuni are being sequenced for further comparative studies.
