In vitro efficacy of 0.2% and 0.4% sodium oxychlorosene against meticillin-resistant Staphylococcus pseudintermedius.

BACKGROUND: There is a need for alternative topical therapies as a consequence of the increased prevalence of meticillin-resistant Staphylococcus pseudintermedius (MRSP) skin infections in dogs. Sodium oxychlorosene has been used as a topical antibacterial agent in human medicine since 1955. OBJECTIVES: To determine whether 0.2% and 0.4% sodium oxychlorosene solutions have a bactericidal effect (>3-log reduction) on MRSP strains isolated from canine skin infections. METHODS AND MATERIALS: A genetically heterogeneous collection of MRSP isolates from dogs was assembled from laboratories across the United States. Time-kill assays were performed with 0.2% and 0.4% sodium oxychlorosene on a 0.5 McFarland standard [approximately 108 colony-forming units (cfu/ml)] suspension of each strain. The average bacterial counts (cfu/ml) of each MRSP strain then were determined at 5, 10, 20 and 60 s after exposure to sodium oxychlorosene; cfu/ml data were converted to log10 scale to calculate microbial reduction. RESULTS: The average bacterial counts following exposure to the 0.2% solution at 5, 10, 20 and 60 s were 6.94 × 104 , 5.63 × 103 , 2.96 × 102 and 1.48 × 102  cfu/ml, respectively. For the 0.4% solution, the average bacterial count at 5 s was 2.12 × 103  cfu/ml. No bacterial growth was observed for any MRSP strain by 10 s. The greatest reduction in cfu/ml occurred within 5 s following exposure to each solution 3.4-log and 4.9-log reduction for 0.2% and 0.4%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: 0.2% and 0.4% sodium oxychlorosene solutions have a bactericidal effect (>99.9% reduction) against MRSP in vitro. Further in vivo studies are necessary to determine whether it is an appropriate alternative therapy for canine pyoderma.

Pathology in Practice.

In collaboration with the American College of Veterinary Pathologists.