Background: Gut dysbiosis and an inflamed bowel are growing concerns within mammals, including dogs. Probiotic supplements are safe and effective for restoring the natural microbial community and improving gastrointestinal health. The biofilm formation, antimicrobial activities, and immunological responses of probiotics are crucial to improving gut health and thus were analyzed in this study.

Method: We tested a commercial probiotic blend (LabMax-3), a canine kibble additive, comprising Lactobacillus acidophilus, Lacticasibacillus casei, and Enterococcus faecium, for itsability to inactivate common enteric pathogens on agar plates, itsability to form biofilms on plastics, and its epithelial cell adhesion and immunomodulatory response on the Madin--Darby Canine Kidney (MDCK) cell line.

Results: The probiotic LabMax-3 blend or individual isolates showed a strong inhibitory effect against Salmonella enterica serovar Typhimurium, Listeria monocytogenes, enterotoxigenic Escherichia coli, and Campylobacter jejuni. In contrast, heat-killed and probiotic cell-free supernatants did not show any inhibition. LabMax-3 formed a moderate biofilm compared to Staphylococcus aureus cultured for 72 h, further confirmed by microscopic imaging. LabMax-3 adhesion to the MDCK cell line (with or without lipopolysaccharide (LPS) pretreatment showed comparable adhesion (P<0.05) to Lacticasibacillus casei ATCC 334, used as a control, which was further verified by Giemsa staining. LabMax-3 also did not show any cytotoxic effects on the MDCK cell line, as measured by lactate dehydrogenase assay. The IL-10 and TNFα ratio of LabMax-3, compared to the L. casei control, showed a significant increase (P<0.05), indicating a more pronounced immunomodulatory effect. TGFβ showed no significant differences between LabMax-3 and L. casei treatment.

Conclusions: LabMax-3, a canine kibble additive, can potentially improve canine gastrointestinal health.