Antimicrobial activity of ear cleanser products against biofilm and planktonic phases of Staphylococcus spp. and Pseudomonas spp. isolated from canine skin and ear infections.

Abstract Background: Staphylococcus spp., and Pseudomonas spp., including multidrug resistant staphylococci are frequent isolates from canine otitis externa and atopic dermatitis. Biofilm formation by these organisms may be important in otitis chronicity. With ear cleanser products commonly used to control microbial overgrowth, it is important to measure their antibiofilm effects. Six ear cleansers (EpioticⓇ SIS, EpioticⓇ Advanced, CleanauralⓇ, Otifree, PeptivetⓇ and SonotixⓇ) were evaluated against infection isolates of Pseudomonas aeruginosa , methicillin resistant and sensitive Staphylococcus aureus and Staphylococcus pseudintermedius . Antibiofilm activity was measured colorimetrically via the presence of viable cells as detected by the reduction of a thiazolyl blue tetrazolium bromide compound (MTT). Minimum inhibitory concentration (MIC) of EpioticⓇ SIS and EpioticⓇ Advanced were measured using a broth micro-dilution assay to ascertain inhibition in planktonic phase. Results: EpioticⓇ (SIS and Advanced), CleanauralⓇ and PeptivetⓇ showed strong antibiofilm activity, with Otifree and SonotixⓇ showing moderate to low antibiofilm activity. Differences in inhibition between the methicillin resistant and sensitive staphylococcal isolates were also observed between the products with Otifree showing significantly less inhibition of the resistant isolate of S. aureus compared to the sensitive isolate. P. aeruginosa biofilms were less effectively disrupted by some ear cleansers compared to EpioticⓇ, and the MIC results indicated that less diluted solutions were required to inhibit this isolate compared to the staphylococci. Differences in the antibacterial effects between EpioticⓇ SIS and EpioticⓇ Advanced solutions could also be detected from the MIC assays suggesting differences in formulations can affect antimicrobial efficacy. Conclusions: Commonly used canine ear cleanser products showed activity against multidrug resistant and sensitive Staphylococcus spp. and P. aeruginosa isolates in both biofilm and planktonic phases. Differences between strains and cleansers were observed that should enable better targeted use of these products.