The R-factors of multiple antibiotic resistant faecal coliforms isolated from a domestic dog

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Abstract
The antibiotic resistant fecal flora of a domestic dog with an acute enteric infection was examined. The flora exhibited overall resistance to a wide variety of antibiotics. Following restoration of the animal to normal health, overall resistance to ampicillin (Ap), tetracycline (Tc), chloramphenicol (Cm) and streptomycin (Sm) was lost, although low numbers of bacteria resistant to these 4 antimicrobial agents could still be isolated up to 1 yr later. Of 11 strains purified for further study, all were positively identified as Escherichia coli and were resistant to various combinations of the above antibiotics and to kanamycin (Km). Each strain harbored 1-5 plasmids, although only 4 proved capable of transferring antibiotic resistance to E. coli K-12. One strain harbored 2 conjugal plasmids, pNJ101 (60 medadaltons [Md]) and pNJ102 (133 Md), which coded for resistance to Cm, Tc, Ap and Cm, Tc, Km, respectively. A 3rd plasmid, pNJ103 (29 Md) was cryptic. The possession of both plasmids pNJ101 and pNJ102 appeared unstable since variants harboring 1 or the other plamsid arose.