Journal of Dental Research, Vol 70, 1252-1257, Copyright © 1991 by International & American Associations for Dental Research Online Journals
Changes in strains of mutans streptococci induced by treatment with chlorhexidine varnish
K. Kozai, D. S. Wang, H. J. Sandham and H. I. Phillips
Faculty of Dentistry, University of Toronto, Ontario, Canada.
Isolates of mutans streptococci were obtained from the dental plaque of ten
subjects before and after the subjects had been free of detectable mutans
streptococci for a mean period of 14.6 weeks (range, from two to 36 weeks).
The mutans streptococci had been rendered undetectable by chlorhexidine
varnish treatment. Examination of the restriction endonuclease analysis
(REA) patterns of the isolates revealed that all ten subjects had one
strain (REA type) after re-appearance of the mutans streptococci that was
identical to one that had been present before the varnish treatment. In six
of the ten subjects, only one strain was detected both before and after
treatment. Each of the other four subjects appeared to gain a new strain
after treatment; one of the four appeared to lose one strain, and another,
four strains. The ability of strains to persist after the period of
undetectability seemed unrelated to their resistance to chlorhexidine or to
their ability to exhibit insoluble glucan-mediated adhesion. In the
subjects harboring multiple REA types, one-seventh of the tooth surfaces
sampled harbored two strains simultaneously, suggesting an inability of
either strain to exclude the other aggressively. Overall, the study
indicated that every subject receiving chlorhexidine varnish therapy had a
primary strain of mutans streptococcus that re-emerged after treatment. In
contrast, secondary strains were highly susceptible to being lost or
gained.
