Comparison of the in vitro antibiofilm activities of otic cleansers against canine otitis externa pathogens.

BACKGROUND

Biofilm production by canine otitis externa (COE) pathogens and resistance development to multiple antimicrobials are commonly reported problems in veterinary practice. The use of adjuvants to disrupt biofilms may be a viable adjunctive therapy.

HYPOTHESIS/

OBJECTIVES

To compare the in vitro antibiofilm activity against COE pathogens of three otic cleansers: PHMB-EDTA (poly [hexamethylene] biguanide hydrochloride and disodium edetate), N-acetylcysteine (NAC) and Triz-EDTA.

ANIMALS/ISOLATES: Thirty isolates of each species, including Staphylococcus pseudintermedius, Pseudomonas aeruginosa, Streptococcus canis, Proteus mirabilis, Escherichia coli, and Malassezia pachydermatis, were collected from COE cases and stored at -80°C until tested.

METHODS AND MATERIALS: Biofilm production was determined by Congo-red agar and microtitre plate-assay methods. Ten of the best biofilm-producing isolates per species were selected to determine minimum biofilm eradication concentration (MBEC) values. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined to compare MBEC/MIC and MBEC/MBC.

RESULTS

PHMB-EDTA possessed antibiofilm activity at low concentrations (MBEC range 3.9/2.3-500/300 μg/mL) against all tested COE pathogens. NAC demonstrated antibiofilm activity for all tested bacterial COE pathogens (MBEC range 4,925-19,700 μg/mL); however, most M. pachydermatis isolates exhibited MBEC values >20,000 μg/mL. Triz/EDTA at the highest concentration tested (3,025/19,520 μg/mL) did not demonstrate antibiofilm activity against most COE pathogens except for S. canis (94.5/610 μg/mL).

CONCLUSIONS AND CLINICAL RELEVANCE: PHMB-EDTA had intrinsic antibiofilm activity at low concentrations against all COE pathogens. Therefore, it is likely to be a very effective adjuvant when used in conjunction with other antimicrobials for the treatment of COE caused by biofilm-producing pathogens.