Dextranases from oral bacteria: inhibition of water-insoluble glucan production and adherence to smooth surfaces by Streptococcus mutans

Abstract

The effect of dextranases (EC 3.2.1.11) from the oral isolates Actinomyces israelii and Bacteroides ochraceus on water-insoluble glucan production by the Streptococcus mutans dextransucrase (EC 2.4.1.5) and sucrose-dependent adherence to smooth glass surfaces by S. mutans was studied. Collection on membrane filters of water-insoluble polysaccharides synthesized from radioactive sucrose was used to demonstrate the marked sensitivity of insoluble glucan formation to the presence of dextranase. Concentrations of A. israelii dextranase as low as 0.002 U/ml inhibited insoluble glucan formation by 60%. Similar results were obtained with the B. ochraceus enzyme. An assay for sucrose-stimulated adherence of S. mutans to smooth surfaces involved attachment of radioactively labeled nongrowing cells to the bottom of glass scintillation vials. This facile and sensitive assay was utilized to demonstrate that sucrose-dependent adherence was affected by low levels of dextranase from either A. israelii or B. ochraceus. Enzyme at 0.005 U/ml reduced adherence of S. mutans by 80%. Treatment of S. mutans cells previously attached to glass with low concentrations of the dextranases resulted in removal of 50 to 60% of the bacteria. These results indicate that dextranase-producing oral bacteria may affect sucrose-dependent colonization of S. mutans on the tooth surface and offer a possible explanation for both the difficulties involved in implanting this bacterium into the human mouth and the limited intraoral transmission of S. mutans from one tooth surface to another. Recent studies in these laboratories (39) demonstrated that a significant proportion of the human dental plaque bacterial flora is capable of producing dextran-degrading enzymes. These bacteria were shown to be a heterogeneous mixture of cell types with varying morphological and biochemical properties. One representative isolate which produces an extracellular endohydrolytic dextranase activity has been identified as Actinomyces israelii (39; R. Staat and C.

Effects of bactericidal treatments on bacterial adherence and dental plaque formation

“…mutans, radiolabeled as described above, were suspended to an optical density of 2.0 at 540 nm in PBS containing 0.2 mM sucrose. Two-ral portions were added to glass vials and incubated at 3?°C for intervals up to 6 h. Such incubation of S. mutans with sucrose fosters attachment of bacteria through glucan formation by the etizyme glucosyltransferase (13). Following aspiration, washing, and drying as described above, the glass vials were assayed lor radioactivity and the number of S. mutaru cells adhering was estimated.…”

Analysis of a dextran-binding domain of the dextranase of Streptococcus mutans

“…sobrinus are predominant producers of the enzyme dextranase (Dex) which cleaves a-1,6-linkages of glucans (Walker et al 1981;Igarashi et al 1992;Wanda and Curtis 1994). The Dex is thought to be responsible both for the control of the amount and content of extracellular glucans and for the metabolic utilization of extracellular glucans (Schachtele et al 1975;Germaine et al 1977;Walker et al 1981;Felgenhauer and Trautner 1983;Colby et al 1995). From these results, the Dex has been thought to be an important determinant of virulence.…”

Molecular Characterization of Dextranase from Streptococcus rattus

“…Dex also possesses an N-terminal signal peptide and a C-terminal sorting signal in VRs (15,18,35). In addition, Dex is thought to be responsible both for controling the amount and nature of extracellular glucans and for utilizing extracellular glucans as a carbohydrate source (5,21,25,28,34). Consequently, Dex is thought to be one of the virulent factors in mutans streptococci.In this paper we sequenced and characterized the dex gene of S. rattus ATCC19645 and compared the Dex molecule of S. rattus with that of S. mutans, S. sobrinus, Streptococcus downei, and Streptococcus salivarius.…”