Abstract
Biofilms are microbial communities that can attach to biotic or abiotic surfaces and are formed as a result of coordinated gene expression of the individual cells via quorum sensing. Biofilm-forming organisms are specifically problematic in the medical field due to their increased resistance to antibiotic treatment. An increase of antibiotic resistance in clinically-relevant strains of bacteria, as well as a decrease in the discovery of new antibiotics have compounded to create a growing infectious disease crisis. Therefore, scientists have turned towards evaluating the clinical application of natural antibacterial agents. Since ancient times, both honey and ginger have been used to treat wounds from infections, however, the antibacterial components of honey and ginger are not fully understood, making them difficult to be applied medically. We tested the compounds Methylglyoxal (MGO), found in New Zealand manuka honey, and Zingerone, found in dry ginger root, as each has been observed to prevent biofilms of both Gram-negative and Gram-positive bacteria. Quorum sensing has been shown to be involved in the control of biofilm formation and production of virulence and colonization factors in a variety of organisms of medical importance. Cell-to-cell signaling is also involved in biofilm dispersion, which is of general and medical interest. The focus of my study was to observe whether or not these compounds prevent biofilms of Bacillus subtilis by disrupting the ComQXPA quorum sensing system, through the use of biofilm and quorum sensing assays. In the biofilm assay, MGO was not effective at reducing biofilm formation in B. subtilis. Zingerone treatment, on the other hand, resulted in a statistically-significant reduction of biofilm formation in this species. Next, a reporter strain was used in a colorimetric assay to measure quorum sensing in the presence and absence of zingerone treatment. Bacteria cultured in the presence of zingerone displayed a statistically-significant decrease in quorum sensing compared to controls. Surprisingly, this effect was also observed when the reporter strain was combined with a hyper-biofilm forming mutant that constitutively overproduces autoinducer signals. Together, these results demonstrate that zingerone can reduce biofilm formation in B. subtilis and that it does so at least in part by blocking quorum sensing between cells. Therefore, zingerone is a potentially promising alternative for antibiotics, or can be used in tandem with antibiotics for both preventing and treating infections caused by biofilm-forming bacteria.