Probiotic Engraftment and Suppression of Canine Otitis Externa Pathogens by Probiotic Ear Drops

Lactobacillaceae have shown promise with their potential to outcompete pathogens and restore a healthy microbial balance in otitis externa (OE).

This study aimed to evaluate the presence of viable Lactobacillaceae over time and in vitro ability to inhibit growth of common OE pathogens.

Fifteen healthy dogs were enrolled and randomised into five groups (n = 3 per group) to receive six probiotic ear drops containing live Lactiplantibacillus plantarum YUN-V2.0 and Lacticaseibacillus rhamnosus YUN-S1.0.

Ear swabs were taken 24, 48, 72, 96 h and 7 days post single application for culturing. For pathogen inhibition, clinical isolates of Pseudomonas aeruginosa, Staphylococcus pseudintermedius and Malassezia pachydermatis were tested against the probiotic ear drop and antimicrobial disks of florfenicol 30 μg, gentamicin 30 μg, marbofloxacin 5 μg, miconazole 10 μg, neomycin 120 μg and terbinafine 1.5 μg.

A relatively basal low abundance of commensal and Lactobacillaceae micro-organisms was detected (1.34 × 10³ colony-forming units [cfu]/mL). At 24 h post-application, Lactobacillaceae increased significantly (2.3 × 10⁶ cfu/mL; p < 0.001), and remained above 10⁵ cfu/mL at 1 week post-application (1.6 × 10⁵ cfu/mL). Lactobacilli demonstrated better growth inhibition of P. aeruginosa than gentamicin and marbofloxacin, and of S. pseudintermedius than gentamicin, neomycin and marbofloxacin. For M. pachydermatis similar growth inhibition versus miconazole and terbinafine was observed.

These results suggest that probiotic strains exhibit excellent retention and can inhibit the growth of S. pseudintermedius, P. aeruginosa, and M. pachydermatis.