Effects of extracellular plaque components on the chlorhexidine sensitivity of strains of Streptococcus mutans and human dental plaque.
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)
D000328:Adult; D002710:Chlorhexidine / Q000494:pharmacology*; D003773:Dental Plaque / Q000378:metabolism* / Q000382:microbiology / Q000503:physiopathology; D005936:Glucans / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008070:Lipopolysaccharides; D008826:Microbial Sensitivity Tests; D010712:Phosphatidic Acids / Q000378:metabolism / Q000494:pharmacology*; D011135:Polysaccharides, Bacterial / Q000378:metabolism / Q000494:pharmacology*; D013295:Streptococcus mutans / Q000187:drug effects* / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D013682:Teichoic Acids / Q000378:metabolism / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
D005936:Glucans; D008070:Lipopolysaccharides; D010712:Phosphatidic Acids; D011135:Polysaccharides, Bacterial; D013682:Teichoic Acids; D014316:Tritium; C009900:lipoteichoic acid; D013395:Sucrose; D002710:Chlorhexidine; D013936:Thymidine