ABSTRACT
BACKGROUND: Antimicrobial resistance may be overestimated in bacterial isolates from clinical samples because veterinarians often submit samples in cases of treatment failure or recurrent cases, which are more frequently associated with resistant strains. HYPOTHESIS/OBJECTIVES: To assess to what extent the prevalence of antimicrobial resistance in Staphylococcus pseudintermedius isolated from first-time superficial pyoderma differs from canine skin isolates from clinical samples with unknown clinical background. ANIMALS: Two study groups were enrolled in Denmark between March 2012 and October 2013: 57 dogs with first-time superficial pyoderma and no prior antimicrobial treatment (Group A); and 289 different dogs for which skin specimens were submitted for culture during the study (Group B). METHODS: One S. pseudintermedius isolate from each dog was confirmed by MALDI-TOF mass spectrometry and tested for antimicrobial susceptibility by broth microdilution. Resistance levels in the two groups were compared by Fisher's exact test. RESULTS: Clindamycin resistance was less frequent in Group A (14%) than in Group B (27%) (P = 0.02). Similar trends were observed for amoxicillin-clavulanic acid (1.8 versus 4.8%), chloramphenicol (8.8 versus 14.5%), enrofloxacin (1.8 versus 3.5%), oxacillin (1.8 versus 4.8%) and trimethoprim/sulfamethoxazole (3.5 versus 5.9%). Oxacillin resistance was significantly associated with resistance to six of seven non-ß-lactams. CONCLUSIONS AND CLINICAL IMPORTANCE: The prevalence of lincosamide resistance is markedly influenced by patients' clinical and antimicrobial treatment history. To limit selection of multidrug-resistant bacteria, lincosamides are appropriate empirical choices for treatment of first-time superficial pyoderma even though resistance is not infrequent. Culture and susceptibility testing are, however, recommended for all pyoderma patients.