Plaque formation in vitro on wires by gram-negative oral microorganisms ( Veillonella)

Abstract

Primary plaque was formed on nichrome steel wires suspended in sucrose media inoculated with Gram-positive filamentous diphtheroids, previously shown to have plaque forming ability. The plaques were then transferred into a Veillonella inoculated lactate medium which supported growth of Veillonella but retarded that of the diphtheroid. Transfer to lactate medium inoculated with Veillonella resulted in considerable increase in the size of the plaque, usually 2–3 grades over that obtained with the diphtheroid alone. Controls consisting of primary plaque incubated in diphtheroid inoculated, as well as uninoculated, lactate media showed no increase in size. In addition, no primary plaque formation was observed with the Veillonella alone. Gram stains of the outer surface of the secondary plaque revealed essentially Gram-negative diplococci. Optical microscopy of toluidine blue stained thick sections of Epon embedded primary plus secondary plaque specimens showed that the plaque was composed of two morphologically distinct types of bacteria. The diplococci appeared to form microcolonies within, as well as around, the matrix formed by the diphtheroid. Electron microscopy supported this finding.