Detection of Streptococcus mutans in plaque samples by the direct fluorescent antibody test.

Culture methods traditionally have been used to isolate and identify bacterial species in clinical specimens. Culture methods are difficult when the specimen is as bacteriologically complex as dental plaque1 and when the organism in question, such as Streptococcus mutans, is present in modest numbers. The fluorescent antibody test (FAT) has been suggested as a potentially simpler method of detecting S mutans in plaque samples.2.3 In the most commonly described procedure, plaque is cultured in broth media and after growth occurs, smears are prepared and stained with fluorescein-conjugated antiserums against the various S mutans serotypes.4,5 This procedure detects whether S mutans is present, but provides no information concerning the proportional levels of S mutans in the plaque samples. Culture studies indicate that the percentages of S mutans in plaque samples show a greater association with dental decay than does the presence of S mutans.6,7 FATs performed on broth cultures of plaque5,8 or upon isolates of S mutans9,10 show that serotype c is the most prevalent serotype in human plaque. However, direct FAT performed on smears of plaque collected from an adolescent male population exhibiting active caries (that is, an average of nine teeth with open lesions) showed serotype d to be the most common serotype, and that serotype c was rarely present.-1 This discrepancy indicates that the human populations sampled had different S mutans serotypes, that the fluorescein-conjugated antiserums used were of different sensitivities, that the anti-d serum reacts with organisms present in the smear that do not grow up in the broth, that the broth or agar cultures