This report is the first to describe the occurrence of sulfate-reducin
g bacteria in the human mouth. Samples of subgingival dental plaque we
re examined for the presence of sulfate-reducing bacteria. Using enric
hment cultures, sulfate-reducing bacteria were detected in 25 (58%) of
43 individuals, and in 39 (48%) of the 82 samples. Pure isolates of s
ulfate-reducing bacteria, obtained from a limited number of enrichment
cultures, belonged to the genera Desulfobacter and Desulfovibrio. The
se genera are also the predominant sulfate-reducing bacteria in the hu
man large intestine. The sulfate-reducing bacteria use sulfate as term
inal electron acceptor to oxidize low-molecular-weight organic compoun
ds, mainly products of microbial fermentation such as acetate, lactate
etc. The numbers of sulfate-reducing bacteria in the mouth are assume
d to be limited by sulfate. Potential sources of sulfate in the subgin
gival area include free sulfate in pocket fluid and glycosaminoglycans
from periodontal tissues.