Welcome to the Kaspar Lab!
Exploring Microbial Interactions within the Human Oral Cavity
Coculture biofilm between Streptococcus gordonii (blue) and Streptococcus mutans (green). Extracellular polymeric substances (EPS) of the biofilm include eDNA (yellow) and glucans produced by S. mutans (red).
Microbes exist within complex communities, often referred to as a microbiome. The human oral microbiome contains over 700+ species living within different niches of the oral cavity. One of those niches are supragingival biofilms, or microbial biofilms attached to the exposed surfaces of teeth. While several species that live in these communities can promote the host’s oral health, others, such as Streptococcus mutans, convert dietary carbohydrates into acid within biofilm structures that can erode the tooth’s enamel causing tooth decay.
Trispecies biofilm of Streptococcus gordonii (blue), Streptococcus mutans (green), and Streptococcus sanguinis (red).
The goal of our research projects are to eliminate disease-associated bacteria such as Streptococcus mutans through microbial ecological engineering — utilizing antagonistic exchanges between microbes to our advantage to specifically target a pathogen of interest, leaving intact health-associated bacteria to promote microbiome homeostasis and the maintenance of the host’s oral health.
Our Latest Research
A strain of Streptococcus mitis inhibits biofilm formation of caries pathogens via abundant hydrogen peroxide production
Authors: Isabella Williams, Jacob Tuckerman, Danial Peters, Madisen Bangs, Emily Williams, Iris Shin and Justin Kaspar
Published on 25th February 2025 at Applied and Environmental Microbiology, ASM Journals
doi: 10.1128/aem.02192-24
Abstract: Commensal oral streptococci that colonize supragingival biofilms deploy mechanisms to combat competitors within their niche. Here, we determined that Streptococcus mitis more effectively inhibited biofilm formation of Streptococcus mutans compared to other oral streptococci. This phenotype was common among all isolates of S. mutans, but was specific to a single strain of S. mitis, ATCC 49456. We documented ATCC 49456 to accumulate four to five times more hydrogen peroxide (H2O2) than other Streptococcus species tested, and 5–18 times more than other S. mitis strains assayed. S. mutans biofilm formation inhibition was dependent on cell contact/proximity and reduced when grown in media containing catalase or with a S. mitis mutant of pyruvate oxidase (spxB; pox), confirming that SpxB-dependent H2O2 production was a major antagonistic factor. Addition of S. mitis within hours after S. mutans inoculation was effective at reducing biofilm biomass, but not for 24 h pre-formed biofilms in an SpxB-dependent manner. Transcriptome analysis revealed responses for both S. mitis and S. mutans, with several S. mutans differentially expressed genes following a gene expression pattern we have previously described, while others being unique to the interaction with S. mitis. Finally, we show that S. mitis also affected coculture biofilm formation of several other commensal streptococci as well as cariogenic Streptococcus sobrinus. Our study shows that strains with abundant H2O2 production are effective at inhibiting initial growth of caries pathogens like S. mutans, but are less effective at disrupting pre-formed biofilms and have the potential to influence the stability of other oral commensal strains.
Importance: Antagonistic properties displayed by oral bacteria have been sought as therapeutic approaches against dental caries pathogens like Streptococcus mutans. An emergent theme has been the ability of select strains that produce high amounts of hydrogen peroxide to effectively inhibit the growth of S. mutans within in vitro and in vivo models. Our study builds on these previous findings by determining that Streptococcus mitis ATCC 49456 is a high hydrogen peroxide producer, compared to other Streptococcus species as well as additional strains of S. mitis. In addition to S. mutans, we show that ATCC 49456 also affects biofilm formation of other oral streptococci, a non-desirable trait that should be weighed heavily for strains under consideration as probiotics. Further phenotypic characterization of strains like S. mitis ATCC 49456 in mixed-species settings will allow us to hone in on qualities that are optimal for probiotic strains that are intended to prevent the emergence of odontopathogens.
A strain of Streptococcus mitis inhibits Streptococcus mutans biofilm formation. Figure 1 from Williams et al 2025.
Kaspar Lab Spring 2025 @ The Ohio State University College of Dentistry Research Day
The Kaspar Lab at the 2025 College of Dentistry Research Day
Top: Left → Right
Robbie Bettinger, Nicole Fleming, Isabella Williams, Allen Choi, and Jacob Tuckerman
Bottom: Left → Right
Justin Kaspar, Alyssa Deever, Huizhen Lim, Hamsika Arnipalli, Sarah Klingerman, and Iris Shin
Kaspar Lab Holiday Party, Fall 2024
Left → Right
Allen Choi, Vince Kawana, Maya Patel, Sarah Klingerman, Isabella Williams, Lindsey Pia,
Iris Shin, Jacob Tuckerman, Alyssa Deever, Jacob Harris, and Robbie Bettinger
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Email: kaspar.17@osu.edu
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