Publication:

Comparative antagonistic activity of probiotic Lactobacillus and Bacillus strains against oral Candida isolates: insights into cell-free supernatant and viable cell-mediated interactions

Background Candida species represent a diverse group of opportunistic yeasts, including clinically important taxa with exhibiting emerging antifungal resistance, complicating the management of oral candidiasis. Probiotic Lactobacillus and Bacillus have emerged as promising adjunctive or alternative agents for controlling oral Candida through antimicrobial metabolite production and competitive interactions.

Methods The antagonistic activity of four commercial Bacillus strains (B. subtilis, B. coagulans, B. clausii, B. mesentericus) and three Lactobacillus strains (L. acidophilus, L. rhamnosus, L. reuteri) was assessed against 160 oral Candida isolates (C. albicans, C. tropicalis, Pichia kudriavzevii, C. parapsilosis). Agar overlay, agar well diffusion and spot assays were conducted to compare the inhibitory potency of viable probiotic cells and their cell-free supernatants.

Results B. coagulans and B. subtilis demonstrated the greatest inhibitory effects across multiple Candida species, followed by notable inhibition from L. acidophilus, L. rhamnosus and L. reuteri. Viable probiotic cells consistently produced zones of inhibition surpassing those observed with cell-free supernatants, highlighting the importance of direct microbial presence and contact in antagonism.

Conclusions The study establishes that probiotic antagonism against oral Candida is largely strain-specific and dependent on assay conditions, with active cellular interactions playing a crucial role. The findings support the therapeutic potential of viable Bacillus and Lactobacillus preparations as biotherapeutic agents in the prevention and management of oral candidiasis.