Lactobacillus probiotics potential in Blastocystis infection: in vitro and in vivo studies.

Blastocystis is a widespread intestinal parasite with debated pathogenicity. Blastocystis infection often persists despite metronidazole therapy, highlighting the need for adjunctive strategies. This study evaluated the therapeutic efficacy of metronidazole, Lactobacillus probiotics, and their combination against Blastocystis infection using in vitro and in vivo models. In vitro cultures of Blastocystis were treated with metronidazole (10 µg/mL), probiotics (10⁸ CFU/mL), or both. Viability and parasite counts were assessed at 24 and 48-hours post-treatment. In vivo, infected mice received metronidazole (20 mg/kg), probiotics (10⁹ CFU/day), or both for 7 days. Parasitological, histopathological, immunohistochemical, and cytokine evaluations were conducted. At 48 h in vitro, metronidazole reduced Blastocystis count by 88.6% and viability by 91.3%; probiotics reduced count by 87.2% and viability by 90.6%. The combination achieved 94.8% and 96.8% reductions, respectively (p < 0.001). In vivo, stool cysts decreased by 86% (metronidazole), 84% (probiotics), and 98.5% (combined). Intestinal cysts decreased by 85.1%, 82.9%, and 98.5%, respectively. Histological improvements and restoration of IgA-secreting cells were most prominent in the combined group. Pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ) decreased most with combination therapy-by 66.9%, 57.8%, and 60.1%, respectively-compared to untreated controls (p < 0.001). These findings indicate that probiotics enhance the efficacy of metronidazole, supporting their role as a promising adjunctive therapy for Blastocystis infection. The combined treatment yielded the most profound parasitological, immunological, and histological improvements, supporting its potential as a superior therapeutic strategy.