Adhesion of Actinomyces viscosus to Porphyromonas (Bacteroides) gingivalis-coated hexadecane droplets

Abstract

Interbacterial adhesion (coadhesion) is considered a major determinant of dental plaque ecology. In this report, we studied several aspects of the adhesion of Porphyromonas (Bacteroides) gingivalis to hexadecane in order to use the liquid hydrocarbon as a convenient substratum for coadhesion assays. Washed suspensions of hydrophobic P. gingivalis 2561 cells were vortexed with hexadecane to yield highly stable cell-coated droplets. Kinetics of coadhesion between Actinomyces viscosus cells and P. gingivalis-coated hexadecane droplets (PCHD) was subsequently studied. Aliquots of PCHD were added to A. viscosus suspensions, and the mixtures were gently rotated. Avid adhesion of A. viscosus cells to the immobilized P. gingivalis layer could be readily measured by the decrease in turbidity in the aqueous phase, following phase separation. Despite the ability of A. viscosus cells to adsorb to hexadecane following vigorous mixing, gentle mixing did not appreciably promote adhesion to bare hexadecane. Moreover, extensive microscopic examinations revealed that A. viscosus cells adhered exclusively to the bound P. gingivalis cells rather than to exposed areas of hexadecane. Coadhesion of A. viscosus to the PCHD appeared to follow first-order kinetics, attaining 80% levels within 30 min. Electron micrographs revealed A. viscosus cells adhering to the P. gingivalis cell layer adsorbed at the hexadecane-water interface. Interestingly, P. gingivalis cells did not appear to penetrate the hexadecane. A. viscosus mutants lacking type 1 or type 2 fimbriae or both were still able to bind to the PCHD. No obvious correlation was observed between relative hydrophobicity of A. viscosus strains and their binding to PCHD. However, defatted bovine serum albumin, an inhibitor of hydrophobic interactions, was the most potent inhibitor among those tested. The data suggest that this approach provides a simple, quantitative technique for studying kinetics of bacterial coadhesion which is amenable to both light and electron microscopic observation.

Enhanced Biofilm Formation and Loss of Capsule Synthesis: Deletion of a Putative Glycosyltransferase inPorphyromonas gingivalis

“…This caused a dramatic change from a hydrophilic to a hydrophobic bacterial surface and an increase in autoaggregation of P. gingivalis cells as a consequence. Similar hydrophobicity data were reported in a previous study that compared the rapid adhesion of strain ATCC 33277 to hexadecane (75% of cells in 4 min) to that of strain W50, a close relative of W83, where only 25% of input cells adhered in the same time period (73). In those experiments, the initial coadhesion of Actinomyces viscosus to P. gingivalis on the surfaces of hexadecane droplets appeared to be preferential and specific.…”

Adhesion of Actinomyces Isolates to Experimental Pellicles

“…The mechanism for this bacterial interaction is probably due to direct interaction between A. n'iscosils and the adhered bacteria (Ellen and Grove, 1989) as was shown by co-aggregation assays (Schwarz et al, 1987) and also by electron microscopy (Rosenberg et al, 1991).…”

Enhanced Biofilm Formation by Escherichia coli LPS Mutants Defective in Hep Biosynthesis

“…The hexadecane hydrophobicity assay is based on bacterial adhesion to hexadecane (specific gravity: 0.773), which has been described previously [40], and was performed with some modifications. In brief, bacteria were collected from an overnight culture and two ml of whole cells standardized at OD 600  = 1 in PBS were placed into a 14-ml polyethylene tube (Falcon352057, BD labware).…”