Small antibiotic resistance plasmids in Staphylococcus intermedius.

Antibiograms and plasmid profiles were evaluated for 116 Staphylococcus intermedius isolates collected from dogs in Germany and in the USA. Of the 26 S. intermedius isolates from Germany, 9 (34.6%) carried plasmids, while 20 (22.2%) of the 90 S. intermedius isolates from the USA were found to be plasmid-positive. Eight small resistance plasmids were identified and characterized using protoplast transformations and restriction endonuclease analyses. Five plasmids (3.8 and 3.9 kb) encoded for chloramphenicol resistance, 2 plasmids (each 2.5 kb) carried determinants for macrolide-lincosamide resistance, and one plasmid (4.5 kb) conferred resistance to tetracycline. Detailed restriction maps of these plasmids were constructed and served for structural comparisons with other small resistance plasmids found in staphylococci. These comparisons implied marked structural homologies with those prototype plasmids initially characterized in S. aureus of human origin.