Professor, Department of Oral Biology
213A Foster Hall
Buffalo, NY 14214
Dr. Ruhl's scientific interest encompasses the general area of oral infection and immunity with major emphasis on the adhesin-mediated interactions of oral bacteria with host salivary or cellular receptors.
Saliva is acknowledged as a major contributor to oral health. Among many other protective functions in the human mouth, saliva helps to maintain an ecological balance within the diverse oral biofilm microbiota through fostering colonization by harmless commensal bacteria that may create a microclimate beneficial for oral health. Already the initial events of bacterial colonization are dependent on saliva, in that certain salivary proteins and glycoproteins, once adsorbed to the oral mineralized or tissue surfaces, serve as adhesion substrates for early colonizing bacteria such as oral actinomyces and viridans streptococci. Many of these early colonizers possess surface adhesins that recognize and bind to cognate peptide or carbohydrate motifs on salivary proteins.
Although the specificities of some of the bacterial adhesins are well characterized, the range of salivary proteins, which serve as receptors for these adhesins, is not fully explored. Past studies in this group have identified salivary proteins that are recognized by the PRP-binding and lectin-like Gal/GalNAc-specific adhesins of oral actinomyces as well as by PRP-binding and sialic acid-specific adhesins of oral viridans streptococci (Ruhl et al. 2004).
Current studies in this laboratory now utilize proteomics methods for a detailed investigation of the full range of salivary proteins and their function as receptors mediating bacterial attachment. As a basis for this goal, proteome maps have been established for whole mixed saliva as well as for the isolated secretions of the major salivary gland (Walz et al., 2006).
Currently, the interaction of salivary proteins with pathogenic bacteria not commonly associated with the oral cavity is being investigated. As an example, the stomach pathogen Helicobacter pylori was selected. This bacterium has recently been found in oral biofilms and was proposed to possess an ecological niche in the oral cavity, which – if true – may have important implications for reinfection of the stomach or transmission between individuals (Bürgers et al., 2008). In a collaborative project with Thomas Borén, Umeå University, Sweden, and Stefan Odenbreit, Max-von-Pettenkofer-Institute, Munich, Germany, isogenetic knock-out mutants of H. pylori, that are deficient in either the sialic acid-binding adhesin (SabA) or in the Lewis-b-binding adhesin (BabA), were used as probes to identify potential salivary receptors that mediate binding of these bacteria (Walz et al. 2005; Walz et al. 2009). Findings resulting from this investigation could help to better understand the role of saliva in the pathogenesis of H. pylori infection including its ability to colonize the oral cavity as an ecological niche.
To obtain a reliable basis for clinical investigations, it is first necessary to test intra- and interindividual as well as age-dependent variations in the composition of salivary proteins. In this context, studies were performed to investigate protein and cytokine composition in individuals with severe gingival disease (Ruhl et al., 2004) as well as longitudinal changes in salivary protein composition during infant development (Ruhl et al., 2005) or differences in salivary protein profiles in children with early childhood caries (Zehetbauer et al., 2009) with the aim to discover clinically relevant indicators among salivary proteins.
In a collaborative project with the Institute of Physical and Theoretical Chemistry, the Department of Operative Dentistry, University of Regensburg, and the Dental School, University of Tübingen, Germany, the influence of surface chemistry of certain biomaterials including those used in the oral cavity on protein adsorption and bacterial adhesion is being investigated (Müller et al., 2006, 2007). Findings from these latter studies may allow to develop strategies to modify biomaterial surfaces in order to minimize bacterial adhesion to biomaterials not only in the oral cavity but also in other regions of the human body.