Emerging chloramphenicol resistance in Staphylococcus lentus from mink following chloramphenicol treatment: characterisation of the resistance genes

A tota of 26 staphylococcal strains isolated from mink with uninary tract infections as well as from the environment of the mink were examined for antibiotic resistance and prevalence of plasmids mediating resistance to the antibiotics applied for prophylactic or therapeutic purposes. Chloramphenicol resistance (Cmr) which occurred in fourteen of the eighteen Staphylococcus lentus strains, but in none of the Staphylococcus intermedius and Staphylococcus xylosus strains, was shown to be mediated by small plasmids of 3.6 to 4.6 kg. On the basis of restriction endonuclease mapping and hybridisation experiments, four different types of Cmr plasmids, designated pSCS14-17, could be distinguished. All these plasmids conferred Cmr by encoding the Cm-inactivating enzyme chloramphenicol acetyltransferase (CAT). In all four types of Cmr plasmids from S. lentus, the expression of the cat genes was inducible with Cm as demonstrated by enzymatic assay and polyacrylamide gel electrophoresis.