The oral microbiome is home to some of the most diverse and vital bacteria. It is important to understand how it works in its home environment and in laboratory settings to see if any discrepancies come from the different settings. It is also important to see how different bacteria interact with each other to either support or hinder different functions of all the bacteria.

Staphylococcus aureus and Staphylococcus epidermidis are among the most common causes of hospital-acquired infections5, 7, 8. Despite the advancements in modern antimicrobials, infections from these organisms can be very difficult to treat, and equally as difficult to prevent 6,7. These organisms’ abilities to form biofilms are directly related to their abilities to cause infections. In biofilms, the staphylococcal species can survive antibiotics and immune responses much better than planktonic cells7. Tolaasin—a toxin and natural biosurfactant produced by P. tolaasii—has been briefly tested against biofilm formation, and the results suggested that it could have inhibitory effects. In order to further confirm and expand upon this potentially useful data, additional testing was performed to determine the effects of tolaasin on the two organisms. In addition, laser treatment was tested on E. faecalis in order to supplement our current understanding of biofilm behavior, and provide additional data to suggest alternative agents against biofilm growth.
This thesis addresses the following questions: What are the best methods to test the effects of tolaasin, cephalexin and laser on the biofilms of S. aureus and S. epidermidis? Does tolaasin prevent or disrupt biofilm formation in S. aureus and S. epidermidis? Does tolaasin work synergistically with cephalexin to prevent biofilm growth and maturation in S. aureus and S. epidermidis? And, what effects does laser treatment have on E. faecalis biofilms? In order to answer these questions, tolaasin was isolated from P. tolaasii, and biofilms were pre-treated with tolaasin. Trials were performed with tolaasin, cephalexin, or a combination of both. The effectiveness of each treatment was determined by observing the biofilm growth. The protocols were then optimized and trials were repeated. Additionally, E. faecalis biofilms were exposed to laser treatment. Using confocal microscopy, the biofilms were observed and quantitative results were used to determine the effectiveness of the treatment. Overall, the results indicated that tolaasin has little effect on biofilm growth. However, further investigation is necessary to confirm these results due to some inconsistent data obtained over the course of the trials. Variations and improvements to the protocol are necessary to accurately determine tolaasin’s potential role in healthcare. Finally, the results of the laser trials suggest that EDTA in conjunction with laser treatment could be useful in cleaning root canals and eliminating post-procedural biofilms—thereby preventing infections.

As a major cause of nosocomial infections, biofilms such as those caused by Staphylococcus aureus and Staphylococcus epidermidis pose large concerns in the field of healthcare due to their extreme durability and resistance to treatment. While all biofilms grow similarly in a series of three stages: 1. Adhesion 2. Maturation 3. Dispersal, Staphylococcal species such as S. aureus and S. epidermidis make use of unique growth factors in order to form prolific and durable biofilms. Due to the prevalence and risks associated with bacteria, many antibacterial methods have been created to treat bacterial infections. Although many antibacterial methods exist, there is still a great need for additional and more effective methods to treat and prevent serious bacterial infections associated with biofilm growth, because incidences of bacterial infection and resistance, especially in medical settings, are on the rise. In recent research, the exotoxin tolaasin, produced by the bacterium Pseudomonas tolaasii has briefly been shown to exhibit antibacterial effects. Based on previous research and tolaasin's observed pore forming and detergent properties, it is hypothesized that tolaasin will disrupt and prevent staphylococcal biofilm growth either independently or synergistically with existing antibiotics. If this is confirmed, tolaasin may have major implications within the future of healthcare, particularly in the field of antibiotics. In order to optimally use tolaasin as an anti-biofilm agent, potential anti-biofilm applications would aim to prevent and treat biofilm infections at the most common sites of biofilm growth such as catheters, medical instruments, implanted medical devices, and surgical sites. In addition, under the assumption that tolaasin will be found effective in inhibiting biofilm growth and infection, this thesis proposes future anti-biofilm technologies that could use tolaasin as an anti-biofilm agent in order to prevent biofilms and associated infections. While there are many potential and promising ways that tolaasin could be used as an anti-biofilm agent in the future, there are still possible limitations that would need to be investigated through further research before these applications can come to fruition. Ultimately, if future research successfully determines that tolaasin can be used to make anti-biofilm technologies that are biocompatible, durable, and effective, then technologies using tolaasin as an anti-biofilm agent may more effectively ensure sterility of medical devices and prevent bacterial biofilms and infections, and may eventually save lives.