Residual antibacterial activity of canine hair treated with topical antimicrobial sprays against Staphylococcus pseudintermedius in vitro.

BACKGROUND Topical antimicrobial therapy is increasingly important in the treatment of canine pyoderma as the incidence of multidrug resistance has risen. However, little information is reported on the persistence of activity of topical antimicrobial products. OBJECTIVE To determine the residual antibacterial activity of canine hairs treated with antimicrobial sprays. ANIMALS Twelve privately owned dogs with no history of dermatological disease. METHODS Dogs were treated once with four different spray products [(A) 1% chlorhexidine digluconate, (B) 2% miconazole nitrate, 2% chlorhexidine gluconate, tromethamine USP/disodium EDTA (TrizEDTA), (C) 3% chlorhexidine gluconate, phytosphingosine salicyloyl and (D) 4% chlorhexidine gluconate, TrizEDTA] in separate 5 × 5 cm sections on the trunk. Hairs were collected via shaving before, one hour after and 2, 4, 7 and 10 days after treatment. Hairs were incubated on agar plates streaked with Staphylococcus pseudintermedius for 24 h and the bacterial growth inhibition zone around the hairs was measured. RESULTS There were significant overall treatment and day (P < 0.0001) differences in inhibition zones. The largest zones of inhibition were from hairs treated with spray B, followed by sprays D, C and A, respectively. All sprays demonstrated residual antimicrobial activity for the ten days evaluated. CONCLUSIONS AND CLINICAL SIGNIFICANCE Results suggest that the efficacy of an antimicrobial spray is dependent on both the concentration and combination of active ingredients. Several ingredient profiles appear to effectively inhibit S. pseudintermedius growth for at least 10 days, which may be beneficial in the treatment of canine pyoderma.