Abstract
Background/Objectives: Infections caused by multidrug-resistant methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains are becoming increasingly common in veterinary medicine. Depending on which tet genes are present, MRSP isolates may exhibit resistance to all tetracyclines or resistance to tetracycline and doxycycline with susceptibility to minocycline. As minocycline may be a potential treatment option, our study aimed to verify this hypothesis. We have compared phenotypic resistance to tetracyclines with the presence of the tet(K), tet(L), tet(M), and tet(O) genes and conducted the molecular characterization of 50 clinical MRSP isolates of canine origin. Methods: The presence of the tet genes was determined by PCR. Molecular characterization included multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. Results: Among the 50 examined clinical MRSP isolates, sequence type ST71 with the SCCmec II-III cassette was predominant (n = 27; 54%). Among these isolates, the tet genes were either absent or present only as the tet(K) gene, resulting in susceptibility to all tetracyclines, tetracycline and doxycycline resistance, and minocycline susceptibility. In contrast, isolates carrying the SCCmec type V cassette (n = 20; 40%) were resistant to all tetracyclines tested and belonged to ST551, ST2851 (new), ST2869 (new) and ST672. These genotypes were most often characterized by the presence of a single tet(M) gene; two genes, tet(M) and tet(K); or three genes, tet(M), tet(K) and tet(O). Notably, 28 out of 50 isolates (56%) showed minocycline susceptibility, and 19 (38%) were minocycline-susceptible and resistant to tetracycline and doxycycline. Conclusions: The obtained results indicate that genotype ST551 and its related ST2851 carry the SCCmec type V and typically contain two or even three tet genes with the tet(M) gene, which confers resistance to all tetracyclines, including minocycline. These genotypes are becoming more common in Poland, and thus, minocycline may be unsuitable for the treatment of MRSP infections in our geographical region. However, in other countries, distinct MRSP genotypes exhibiting minocycline susceptibility may predominate, such as those belonging to clonal complex 71 and carrying the SCCmec type II-III cassette. In the case of such strains, minocycline may be a therapeutic option. Therefore, it is advisable to monitor the spread of MRSP clones carrying different tet genes and exhibiting varying minocycline resistance profiles.