AbstractsBiology & Animal Science

Dental caries is the most prevalent infectious disease of humans and can ultimately result in destruction of affected teeth. Recent studies indicate that there is a resurgence of dental caries occurrence in both developing and developed countries. Current methods of treatment are expensive, and a cost-effective preventative would be of great value. The mutans streptococci (MS) levels present in the human oral cavity provide one measure of the current dental caries activity in the host. Important virulence factors of the MS include their ability to utilise dietary sucrose resulting in: (1) formation of extracellular polysaccharides (EPS) that facilitate their attachment and accumulation within dental plaque; (2) storage of intracellular polysaccharides (IPS) as a latent source of energy and; (3) fermentation with formation of high concentrations of lactic acid. The combination of these activities results in the creation and maintenance of a low plaque pH and subsequent demineralisation of the enamel with associated formation of carious lesions. Current prevention regimens have not adequately limited the development of dental caries. Prophylactic dosing with classical antibiotics has been investigated for the prevention of dental caries, and while this approach can achieve some reduction in both MS levels and caries development it can also seriously damage the protective normal microflora, enhancing the likelihood that opportunistic infections or resistance to medically-important antibiotics may occur. A more focused alternative to the use of classical chemotherapeutic antibiotics may be the deployment of bacteriocins (proteinaceous anti-bacterial agents) which have much narrower inhibition spectra. A potential impediment however to the use of bacteriocins is their relatively large size (most are >2000 Da) which may limit their penetration of the extracellular polysaccharide (EPS) present in the extracellular matrix of dental plaque. A primary objective of this study was to use plaque biofilm models to document the extent to which bacterially-produced EPS interferes with the activity of bacteriocins against the target cells of MS. Several in vitro models were developed and applied to assess the effect EPS has on the inhibitory activity of bacteriocins of different sizes. The enzyme dextranase was then tested for its ability to enhance the penetration of anti-MS bacteriocins within the biofilm environment. Initially, a selection of known bacteriocin-producing bacteria were tested for both their dextranase and anti-MS inhibitory activities. This screen identified Streptococcus salivarius strains JH and M18 as producers of both anti-MS and dextranase activities, with strain JH having particularly strong dextranase activity. Growth of these strains in an in vitro saliva model system enhanced the dextranase activity of both strains when compared to the levels produced in traditional growth media. Further research was undertaken to identify the cause of the enhanced dextranase activity of strain JH. Analysis of the…