[Cariogenicity of Propionibacterium acnes, Streptococcus intermedius and Streptococcus mutans in germ-free rats].

A comparative study has been made on the cariogenic potentials of Propionibacterium acnes ATCC 11828, Streptococcus intermedius OE-1 and Streptococcus mutans OZ-1. The strains of P. acnes and S. intermedius have chondroitinase activity. As metabolic end-products, the P. acnes strain produces mainly a weak acid, propionic acid, whereas strong lactic acid is the main product of the strains of S. intermedius and S. mutans. Five germ-free rats were used for infection with each bacterial strain. The rats were fed with a 25% sucrose diet for 100 days and then sacrificed. The upper and lower molars were used for the determination of the smooth surface caries score. The right upper and lower jaws were used for the preparation of sections which were employed for the determination of the fissure caries score and microradiography. The left upper and lower jaws were decalcified and used for the preparation of thin sections for staining with Gram's, hematoxilin eosin, Mallory's, alcian blue-PAS, silver and toluidine blue stain. The results obtained were as follows: 1. The recoveries of infected cells in the specimens obtained by swabbing the oral cavities were in the order of 10(4) CFU/mg wet weight regardless of the strains injected. 2. Macroscopically, the P. acnes strain decalcified to a lesser extent some of the enamel surfaces of the lower molars. However, the S. intermedius strain produced mainly the fissure caries of the lower molars. The S. mutans strain destroyed the enamel extensively, resulting in the induction of rampant carious lesions. 3. The caries scores of smooth surface determined by Keyes's method were 19.4 +/- 7.8, 46.8 +/- 5.8 and 118.4 +/- 15.4 in the rats infected with the strains of P. acnes, S. intermedius and S. mutans, respectively. The fissure caries score determined by the modified König's method were 8.5, 22.3 and 36.5 in the sections prepared from the rats infected with the strains of P. acnes, S. intermedius and S. mutans, respectively. 4. Microradiography revealed no translucent area in the enamel and dentine of the P. acnes-infected molars, while in the S. intermedius-infected molars translucent areas were found at the dentino-enamel junction neighboring the bottoms of some fissures. The S. mutans-infected molars showed extensive translucent areas over the enamel and dentine of all of the molars. Even defects of the enamel and dentinal areas were observed in some of the molars. 5. The decalcified tooth sections were stained in a similar manner irrespective of the type of organisms used to infect them.(ABSTRACT TRUNCATED AT 400 WORDS)