Variations occur in the flora of different carious cavities, and in the same cavity from day to day. Fusiform bacteria are among the species of oral microorganisms that can produce appreciable quantities of acid in an anerobic environment.
Direct microscopic studies of smears from established carious cavities give no significant evidence of the primary importance of any particular morphologic group of bacteria in caries. In every cavity studied, a complex mixed flora was present. Fusiform bacteria, which occur in great numbers in the mouth, have also been found at the base of established cavities. Of 27 strains of Fusiformis dentium studied, 23 depressed the pH of Douglas broth (plus 2 percent of glucose) to an average of 4.8. In three instances, an average of 2.4 cc. of N NaOH was required to neutralize the acid formed in 100 cc. of medium (other species of Fusiformis produced much less acid).
References: J. Den. Res., 1935; J. Am. Den. Assoc., 1937, 1938; J. Bact., 1937.