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 10(8) 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 60s after exposure to sodium oxychlorosene; cfu/ml data were converted to log(10) 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 x 10(4), 5.63 x 10(3), 2.96 x 10(2) and 1.48 x 10(2) cfu/ml, respectively. For the 0.4% solution, the average bacterial count at 5 s was 2.12 x 10(3) 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