Increased Resistance of Staphylococcus pseudintermedius to the Commonly Used Antibiotics in Canine Dermatology

Increased resistance of Staphylococcus spp. is a growing problem in veterinary medicine. This study was per formed to examine antimicrobial susceptibility of Staphylococcus pseudintermedius and other bacteria isolated from canine skin and ear infections over a 7 year period: 2000-2006. Eighty-six dogs which met predetermined inclusion criteria were examined. Bacterial isolates were examined for susceptibility to four commonly used antibiotics: cephalothin (first generation cephalosporin), amoxicillin-clavulanate, potentiated sulfonamide and enrofloxacin. The degree of susceptibility and the percentage of resistant strains of the bacteria to the antibiotics were compared between two periods: 2000-2002 and 2003-2006. Comparison between sample sites and association between susceptibility and signalment were examined. Resistance of S. pseudintermedius and Proteus spp. to cephalosporins and amoxicillin-clavulanate increased over the years and it was statistically significant for S. pseudintermedius (P=0.018). Susceptibility of S. pseudintermedius to cephalosporins and amoxicillin-clavulanate decreased over the years (P= 0.009). Susceptibility of Proteus spp. to amoxicillin-clavulanate and fluoroquinolones decreased as well ( P=0.037, P=0.055 respectively). More skin than ear isolates of S. pseudintermedius and Proteus were resistant to cephalosporins and amoxicillinclavulanate. More ear isolates of Proteus were resistant to potentiated sulfonamides (P= 0.039). All isolates of Proteus from mix breed dogs, but not from German shepherds were resistant to cephalosporins (P=0.032). This study showed an increased resistance and decreased susceptibility of two common bacteria found in dogs' skin and ear infections. These findings should encourage clinicians to submit samples for culture and susceptibility before commencing antibacterial therapy, so as to provide a more accurate therapeutic decision and avoid unnecessary antibiotic use.