How long dog hair stays antibacterial after shampoo treatment

Abstract

BACKGROUND: Topical antimicrobial treatment for canine pyoderma is becoming increasingly important, but little is known about the mechanism of action and persistence of activity of antimicrobial shampoos. OBJECTIVE: To determine the residual antimicrobial activity on canine hairs treated with antimicrobial shampoos. ANIMALS: Forty-two dogs from a research institution. METHODS: Dogs were treated with six different shampoos and the combination of one shampoo and conditioner containing benzoyl peroxide, chlorhexidine in different concentrations (0.8, 2, 3 and 4%), ethyl lactate and miconazole twice weekly for 2 weeks. A shampoo vehicle without antimicrobial ingredients was used as the control. Hairs were collected immediately after and 2, 4 and 7 days after the last shampoo therapy and placed onto an agar plate streaked with Staphylococcus pseudintermedius. After incubation, the growth inhibition zone around the hair shafts was measured. RESULTS: The largest zone of inhibition of bacterial growth was seen after shampoos containing 2 and 3% chlorhexidine and the combination of chlorhexidine shampoo and conditioner. The zone of inhibition was smaller with the shampoos containing 0.8 and 4% chlorhexidine. There was no difference between the inhibition zones post-treatment with benzoyl peroxide, ethyl lactate and control. CONCLUSION AND CLINICAL IMPORTANCE: The efficacy of a shampoo is dependent not only on the concentration of the active ingredients but also on the shampoo formulation. Hair shafts treated with shampoos containing 2 and 3% chlorhexidine and the combination of shampoo and conditioner inhibited bacterial growth significantly and seem suitable to treat canine bacterial pyoderma.