Dairy Propionibacteria: Probiotic Properties and Their Molecular Bases

Dairy propionibacteria are commonly ingested through the consumption of raw milk cheeses or Swiss type cheeses in which they are added as starter cultures. Some strains of the species Propionibacterium freudenreichii or their culture media have been commercialized in multi-strain probiotic preparations or to supply bioactive substances such as short chain fatty acids, bifidogenic molecules and vitamins, respectively. In recent years, many more mechanisms of action of dairy propionibacteria as probiotics for different novel applications were discovered and are summarized in this descriptive review. Strains of P. freudenreichii mitigated inflammatory bowel diseases (IBDs), mucositis and prevented necrotizing enterocolitis (NEC) in preterm newborns. Moreover, these bacteria exerted immunomodulation, particularly in food allergy, anti-obesity, anti-diabetic, anti-cancerogenic effects, inhibition of osteoclastogenesis in rheumatoid arthritis, and infection mitigation in animal models. Most of the observed effects were mediated by cell surface proteins or extracellular vesicle (EV) proteins such as the surface layer (S-layer) protein SlpB, DlaT and GroEL. Based on the available information, these bacteria do not present safety issues but investigations on the presence of transferable antibiotic resistance traits should be specifically assessed both phenotypically and genotypically. In most possible applications the confirmation of beneficial effects in clinical trials still need to be carried out to allow their use as health promoting agents.