Date of Award


Document Type

Honors Thesis

Degree Name

Bachelor of Science



Advisor/Committee Chair

Alex Valm


The gram-positive bacterium Actinomyces naeslundii is a core member of the oral microbiome and has been associated with states of health. In early human life, researchers unraveled the involvement of several different taxa of microbes present within the oral cavity in contributing to diseases including tooth destruction. Periodontitis is a prevalent oral disease that is proposed to be caused by dysbiosis, which is characterized by microbial shifts within the bacterial community resulting from changes in relative microbial abundance and spatial organization in the dental plaque microbiome, causing immense gum pain and inflammation. Corynebacterium matruchotii is also a gram-positive bacterium like Actinomyces. We hypothesize that A. naeslundii inhibits the growth of C. matruchotii due to the secretion of toxic metabolites by A. neasulundii when grown in the same colture. To test this hypothesis, we quantified the effect of A. naeslundii spent media and A. naeslundii heat-killed cells on the growth kinetics of C. matruchotii. To begin, we cultured A. neasulundii, then harvested the spent media and heat-killed the cells for the downstream experiment. We then tested different concentrations of spent media [25%, 50%, 75% ,75 %. and 100%] and heat-killed cells on C. matruchotii growth using optical densitometry. To further determine and quantify how long the C. matruchotti cells grew and the active replication occurring (by measuring nucleoids) within the cell, we performed cell plate counting to see how many colonies and cells were present in the culture at that time and then fluorescence in situ hybridization (FISH) using genus-specific Corynebacterium FISH probes and DAPI. Collectively, the experiments furnished results that revealed a significant reduction in the measured optical densities (ODs) with an escalating concentration of spent media, although with heat-killed cells, the results exhibited a decrease in OD readings as well as the spent media. In turn, the findings from the numerous experiments offer more insights into comprehending metabolic interactions that facilitate the organizational dynamics of dental plaque structure in relation to periodontitis.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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