A pilot study comparing in vitro efficacy of topical preparations against veterinary pathogens.

Background - Topical antimicrobial agents are important for the management of cutaneous infections. For topical antimicrobial agents, in vitro efficacy data are limited. Objectives - To determine and compare the minimum bactericidal/fungicidal concentrations (MBCs/MFCs) of several topical antimicrobial agents against veterinary pathogens. Materials and methods - Two chlorhexidine, two oxychlorine based products (NaOCl & HOCl) lime sulfur (LS), manuka honey (MH) and hydrocortisone aceponate (HCA) were tested against American Type Culture Collection (ATCC) and clinical isolates: meticillin susceptible and resistant Staphylococcus pseudintermedius (MSSP), qac A/B carrying MSSP, antimicrobial susceptible and extended spectrum beta-lactamase producing Escherichia coli, multidrug-resistant Pseudomonas aeruginosa and Malassezia pachydermatis. The MBCs/MFCs were measured, where available, using a broth microdilution method; isolates were incubated for 3 and 10 min. Results - Chlorhexidine and isopropyl alcohol (Chl(1)) showed significantly lower MBCs (0.46 mg/L - 937.50 mg/L, P = 0.027) compared to chlorhexidine and climbazole (Chl(2), 58.59 mg/L-1875 mg/L). NaOCl and HOCl showed excellent antimicrobial activity with HOCl having significantly lower MBCs compared to NaOCl (0.03 mg/L1.72 mg/L and 0.03 mg/L-1.95 mg/L, respectively, P = 0.042). The detectable MBCs for LS and HCA were high, being close to the starting concentration (5,000 mg/L and 146 mg/L, respectively). The MBC/MFC for MH was not detectable. Amongst all test products there was no significant effect of contact time or isolate resistance status. Conclusions and clinical importance - Chlorhexidine, NaOCl and HOCl demonstrated low MBCs against tested organisms, suggesting potential in vivo efficacy. The selection of an appropriate antimicrobial agent, however, cannot be based exclusively upon MBC/MFC data; other factors should be considered.