CONICET | Buscador de Institutos y Recursos Humanos

Stimulatory effect of probiotic Bacillus subtilis on innate immune response. Saball E., Salvarrey M., Spalding T., Rovetto A., and Grau R. Facultad de Ciencias Bioquímicas y Farmacéuticas - UNR. IBR-CONICET. Rosario, Argentina. Generation of a protective barrier against harmful microorganisms by colonizing and coating the intestinal mucosa as well as stimulation of non-specific immune response are implicated in probiotic effects. A new generation of probiotics is represented by human-friendly Bacillus subtilis spores. Once in the gut, spores germinate and the vegetative forms produce the probiotic effect. Therefore, it is interesting to investigate the effect of probiotic B. subtilis on (i) complement system activation (CSA) and (ii) interference with pathogen adherence. In addition, we explore the putative role of the master regulatory transcription factor Spo0A in these processes. CSA was investigated employing inhibition haemolytic assays for classical and alternative pathways and determining the activation products. In vitro experiments were performed incubating B. subtilis strains with normal human serum (A) while for in vivo experiments we analysed serum (B) and peritoneal fluid (C) of Wistar rats intraperitoneally inoculated. In all cases (A-C) Spo0A+ cells activated both pathways with inhibition percentages between 48% to 55% and presence of activation products. Bacterial Fn-binding was measured by ELISA and FITC-labelled bacteria were used for competitive binding assays. Spo0A+ cells showed a strong binding to Fn (Kd 0.26 nM) and were capable to inhibit competitively S. aureus binding. Interestingly, Spo0A- cells failed to activate complement and were unable to block the Fn-adherence of the pathogen. Overall, this investigation brings about novel results of probiotic B. subtilis on the stimulation of the innate immune response (CSA) and the key role of the regulatory protein Spo0A in this process.