Dietary Sugars, bacterial colonization and the behavior of fruit flies

Abstract

Cavity remains prevalent in young children today. One major contributor is the modern diet, specifically the large amounts of dietary sugars consumed. Another key factor is bacteria in our mouth that eat these sugars. Streptococcus mutans among other acid producing bacteria is one of the leading microbes that initiate and promote cavity (tooth decay). It metabolizes sugars to produce plaque, which can build up over time and simultaneously increase acid production that causes cavity. So studying how quickly different sugars affect Streptococcus mutans colonization is important to understand the development of cavity and its impact on host behavior. My hypothesis was that S. mutans breaks down some sugars more efficiently and as a result, can colonize more quickly with some than others and produce more acid, thus impacting host behavior.To study bacterial colonization, I used a fruit fly model because fruit flies like sugars and Streptococcus mutans can readily colonize fruit flies when is mixed with sugars. Each sugar solution was mixed with green fluorescent protein (GFP) labeled S. mutans and fed fruit flies. We then waited for 6 days to let flies eat and grow at room temperature. After this incubation period, we took flies out every 2 days to image the green color under the fluorescent microscope, which indicates S. mutans colonization. On the final day, we took all of the remaining flies, ground them up, and performed appropriate dilutions to plate and count bacterial colonies, which represents bacterial colonization of flies. Colonization of flies fed with five different sugars by S. mutans was monitored by direct imaging and counting bacterial colony forming units. Flies fed with sucrose exhibited the best colonization, while flies fed with xylitol did not show any colonization. The pH values of S. mutans cultures (pH adjusted to 7.5) fed with different sugars were monitored using a pH meter. With all sugars, the pH dropped significantly after five minutes. The pH dropped below 4.5 with sucrose that supports the best colonization. The pH dropped at an average of 2.91 during the 30 minutes testing period, suggesting sugars and bacteria fuel acid production.Furthermore, flies colonized by S. mutans fed with sucrose were monitored for their behavior (locomotion) using beam breaks and analyzed by DAMsystems308 software. Sucrose fed flies exhibited more bacterial colonization and became hyperactive. Overall the data indicated that S. mutans utilizes some dietary sugars more efficiently and as a result, can colonize better, produce more acid and become more active. Our studies demonstrated that the interactions between bacteria and sugars are important for the development of cavity and impact host behavior.