Date of Completion

Spring 5-1-2016

Thesis Advisor(s)

Patricia Rossi

Honors Major

Molecular and Cell Biology


Bacteriology | Oral Biology and Oral Pathology


The overgrowth and disequilibrium of pathogenic microorganism species both native and non-native to the oral cavity can manifest into a variety of different oral diseases, pathologies, and afflictions in humans, including dental caries, gingivitis, pharyngitis, halitosis, and oral candidiasis. Two bacterial strains with clinically-significant probiotic applications in curtailing the pathogenic bacterial growth involved in these conditions are Streptococcus salivarius strain K12 and Streptococcus salivarius strain M18. To summarize the most up-to-date in vitro, in vivo, and clinical research findings, administration of these S. salivarius strains typically in the form of probiotic lozenges results in colonization, reduction in inflammatory measures, and marked alterations to physical structure & gene expression of the oral epithelial cells of the pharynx, tongue, and buccal membrane. While K12 and M18’s reduction of pharyngitis and halitosis has been largely attributed to bacteriocin production, the probiotic strains utilize different modes of action to reduce other oral pathologies. The prevention of dental caries, gingivitis and oral candidiasis appears to be ultimately influenced by K12 and M18’s production of dextranase & urease, reduction of inflammatory cytokines, and direct physical attachment to pathogens, respectively. In addition to conferring several oral health benefits, these S. salivarius strains have been proven extremely safe for human consumption in clinical trials and have the potential for universal application as an alternative treatment to antibiotics in the aforesaid oral pathologies.