Journal of Dental Research, Vol 64, 1051-1054, Copyright © 1985 by International & American Associations for Dental Research Online Journals
Effects of extracellular plaque components on the chlorhexidine sensitivity of strains of Streptococcus mutans and human dental plaque
L. E. Wolinsky and W. R. Hume
An in vitro study was undertaken to determine the effects of
sucrose-derived extracellular plaque components on the sensitivity of
selected oral bacteria to chlorhexidine (CX). Cultures of Streptococcus
mutans HS-6, OMZ-176, Ingbritt C, 6715-wt13, and pooled human plaque were
grown in trypticase soy media with or without 1% sucrose. The sensitivity
to CX of bacteria grown in each medium was determined by fixed-time
exposure to CX and subsequent measurement of 3H-thymidine uptake. One-hour
exposure to CX at concentrations of 10(-4) M (0.01% w/v) or greater
substantially inhibited subsequent cellular division among all the S.
mutans strains and human plaque samples tested. An IC50 (the CX
concentration which depressed 3H-thymidine incorporation to 50% of control
level) of close to 10(-4) M was noted for S. mutans strains HS-6, OMZ-176,
and 6715-wt13 when grown in the presence of sucrose. The same strains grown
in cultures without added sucrose showed about a ten-fold greater
sensitivity to CX (IC50 close to 10(-5) M). A three-fold difference was
noted for S. mutans Ingbritt C. Only a slight increase in the IC50 was
noted for the plaque samples cultured in sucrose-containing media, but
their threshold for depression of 3H-thymidine uptake by CX was lower than
that for the sucrose-free plaque samples. The study showed that
extracellular products confer some protection against CX to the bacteria
examined, and provided an explanation for the disparity between
clinically-recommended concentrations for plaque suppression and data on in
vitro susceptibility.(ABSTRACT TRUNCATED AT 250 WORDS)
