Frequency and stability of mono- or poly-infection by Actinobacillus actinomycetemcomitans serotypes a, b, c, d or e

The aims of the study were to determine the prevalence of simultaneously multiple Actinobacillus actinomycetemcomitans serotypes in one individual, stability of infection by the same serotype and the occurrence of previously not described serotypes of A. actinomycetemcomitans. The serotypes of 515 clinical isolates of A. actinomycetemcomitans from 91 Finnish, Caucasian subjects, including 321 follow-up samples from 51 subjects, were determined with immunodiffusion assay. Most subjects (n = 86, 95%) were infected with one serotype only; 466 (91%) isolates from 80 subjects belonged to serotype a (25% of isolates/25 subjects), b (25% of isolates/27 subjects) or c (41% of isolates/30 subjects). Fifteen isolates from 4 subjects reacted with the antiserum raised against previously untypable clinical strain IDH 781 (serotype d) and 18 isolates from 5 subjects with the antiserum raised against strain IDH 1705 or IDH 3096 (serotype e). Sixteen (3%) isolates from 5 subjects remained untypable. The same infecting A. actinomycetemcomitans serotype(s) persisted for the 1-6 years of follow-up. In conclusion, the study indicates a rare simultaneous occurrence of multiple oral A. actinomycetemcomitans serotypes, the stability of infection by the same serotype(s) and the existence of serotypes of A. actinomycetemcomitans not previously described.