Investigating novel therapeutic agents in the treatment of canine otitis externa caused by Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is a ubiquitous micro-organism and opportunistic pathogen frequently isolated from chronic otitis externa infections in dogs, a painful condition which is very difficult to treat, due in part to multi-drug resistance (MDR) and the production of biofilms. When medical management fails, the only course of treatment involves radical surgical intervention, which results in permanent deafness in the affected ear. P. aeruginosa is also an important human pathogen. The World Health Organisation listing some strains as a “critical” priority pathogen for which new antimicrobials are desperately needed. There is growing concern over veterinary isolates acting as a source of resistant pathogens for the human infections. However, the number of new antibiotics in development is very limited.

Therefore, identifying novel antimicrobial treatments against P. aeruginosa is important for both human and animal health.

Bacteriocins are ribosomally synthesized antimicrobial peptides (AMPs) that are produced by bacterial cells to facilitate competitive advantage in diverse populations.

This study aimed to identify canine commensal bacterial isolates that produce bacteriocins with inhibitory activity against P. aeruginosa and their biofilms. Skin swabs were obtained from 24 healthy dogs from around the nose, mouth, axillae, inguinal skin, and anus, from which 84 commensal organisms were isolated. Twenty-five P. aeruginosa samples from canine ear canals were used in this study, of which 84% were biofilm producers.

The bacteriocin investigation used deferred antagonism assays and cell-free supernatant assays to screen for inhibitory activity, which identified several test isolates that inhibited both biofilm production and overall growth. Genomic analysis identified one known bacteriocin (lichenicidin) and three potentially novel putative bacteriocins with promising inhibitory activity against sample strains. Based on the results in this study, it is likely that at least one of the bacteriocins identified is responsible for the antimicrobial activity observed in laboratory testing. Further investigation is required to confirm the potential of these bacteriocins as candidates for development of novel therapies for the treatment of P. aeruginosa canine otitis infections.