Investigations into the basis of chloramphenicol and tetracycline resistance in Staphylococcus intermedius isolates from cases of pyoderma in dogs

A total of 160 Staphylococcus intermedius isolates were recovered from cases of pyoderma in 2002 and were examined for susceptibility to 13 different antimicrobial agents. Ninety per cent (144) of the isolates were resistant to tetracycline, derivatives of which have been used until recently, and 18% (29) were resistant to chloramphenicol which was banned from use 13 years ago. The presence of genes encoding chloramphenicol acetyltransferase (CAT) and tetracycline resistance (tet); tet(K), (L), (M), and (O) were determined by PCR in the 29 chloramphenicol and tetracycline resistant isolates. Seventeen (59%) isolates contained the cat gene while 12 (41%) isolates did not carry the cat gene, implying there may be other genes for chloramphenicol resistance that were not detected by the primers (primer set 1) used in this study. The tet(M) gene was found in 28 (97%) of the resistant S. intermedius isolates, but none contained the tet(O) gene. All 29 isolates carried one or two tet genes; tet(K), (L), and (M), with four different distribution patterns. New PCR products, a 1.1 kb product using primer set 1 and a 0.2 kb product using primer set 2, were cloned and sequenced. A 904 bp fragment of S. aureus plamid pS194, including sequence from the streptomycin adenyltransferase gene (804 bp), was found inserted into the terminal region of the cat gene (GenBank accession no. AY604739), whilst the sequence of 0.2 kb was previously unpublished.