Extracellular Glycoside Hydrolase Activities in the Human Oral Cavity

Abstract

ABSTRACTCarbohydrate availability shifts when bacteria attach to a surface and form biofilm. When salivary planktonic bacteria form an oral biofilm, a variety of polysaccharides and glycoproteins are the primary carbon sources; however, simple sugar availabilities are limited due to low diffusion from saliva to biofilm. We hypothesized that bacterial glycoside hydrolase (GH) activities would be higher in a biofilm than in saliva in order to maintain metabolism in a low-sugar, high-glycoprotein environment. Salivary bacteria from 13 healthy individuals were used to growin vitrobiofilm using two separate media, one with sucrose and the other limiting carbon sources to a complex carbohydrate. All six GHs measured were higherin vitrowhen grown in the medium with complex carbohydrate as the sole carbon source. We then collected saliva and overnight dental plaque samples from the same individuals and measuredex vivoactivities for the same six enzymes to determine how oral microbial utilization of glycoconjugates shifts between the planktonic phase in saliva and the biofilm phase in overnight dental plaque. Overall higher GH activities were observed in plaque samples, in agreement within vitroobservation. A similar pattern was observed in GH activity profiles betweenin vitroandex vivodata. 16S rRNA gene analysis showed that plaque samples had a higher abundance of microorganisms with larger number of GH gene sequences. These results suggest differences in sugar catabolism between the oral bacteria located in the biofilm and those in saliva.