Antimicrobial activity of Lactobacillus casei on Staphylococcus pseudintermedius isolates.

Background: Antimicrobial resistance is increasing each year. For example, in 2019 it was directly responsible for an estimated >1 million deaths. Additionally, the development of new drugs is much slower, generating enormous concerns about responses to infection in the future health scenario. Therefore, probiotics have emerged as an alternative to antibiotics.

Objectives: This study aimed to isolate and identify a Lactobacillus casei from healthy canine skin and investigate its antimicrobial effect on isolates of Staphylococcus pseudintermedius originating from dogs with pyoderma.

Materials and methods: L. casei was isolated from skin samples collected with a sterile cotton swab from the inner pinnae of healthy dogs. It was then cultured, identified using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry, and tested against 30 different clinical isolates and one American Type Culture Collection strain of S. pseudintermedius using the spot-on-the-lawn technique. Its safety was assessed through a modified Kirby-Bauer disc diffusion susceptibility test.

Results: L. casei inhibited the growth of all isolates of S. pseudintermedius. The mean value of the inhibition halo of all isolates was 11.3 mm. A significant positive correlation (Pearson's linear correlation = 0.444; p = 0.014) was noted between the inhibitory halos formed by L. casei on the S. pseudintermedius isolates and the halos produced by the tested antimicrobial discs on the same isolates. The L. casei strain demonstrated sensitivity to all tested antimicrobials.

Conclusions and clinical relevance: The study indicates that using commensal bacteria from canine skin, specifically L. casei, to control bacterial infections caused by S. pseudintermedius can be a promising complementary or alternative therapy to antibiotics relevant to animal and human health.