Evaluation in vitro of the antimicrobial activity of two topical preparations used in the management of ear infections in the dog.

Products designed for ear cleansing (i.e., Epi-Otic and Epi-Otic New Formula [NF]a) were evaluated in vitro for their ability to kill clinical isolates of Staphylococcus intermedius, Pseudomonas aeruginosa, and the yeast Malassezia pachydermatis. Dilutions of the products at 1/5 and 1/25 in distilled water were inoculated with suspensions of the organisms and held at room temperature. The mixtures were sampled at intervals between 1 and 16 minutes, and numbers of viable colony-forming units of the microorganisms were determined by culture on blood agar or modified Dixon's agar (for the yeast) using the spread-plate method. At a dilution of 1/5, both products were able to eliminate S. intermedius within 1 minute. P. aeruginosa was eliminated within 2 minutes by both products. M. pachydermatis was eliminated by Epi-Otic NF and Epi-Otic within 4 and 8 minutes, respectively. Lower activity was demonstrated following dilution at 1/25. The findings support previously published data for Epi-Otic indicating antimicrobial activity both in vitro and in vivo. The findings suggest that Epi-Otic may be useful in the control of ear infections.