title: Effects of pH on expression of sodium fluoride resistance in Streptococcus mutans.
abstract: Stable fluoride-resistant mutants of Streptococcus mutans GS-5 were isolated on Todd-Hewitt agar by a step-wise selection procedure. Resistance is defined here as the ability to form colonies in 48 hr. First-step mutants demonstrated six different levels of resistance, ranging from 400 to 1000 micrograms/mL sodium fluoride. Second-step mutants demonstrated two levels of resistance, one at 1600 and the highest at 3000 micrograms/mL sodium fluoride. All mutants (originally isolated at pH 7.2) were tested for fluoride resistance at pH 5 and 6. At these lower pH values, all of the mutants demonstrated resistance to fluoride when compared with the parent strain, but at much-reduced levels.
mesh_terms: D003470:Culture Media; D004352:Drug Resistance, Microbial; D005459:Fluorides / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D013295:Streptococcus mutans / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology
chemical_list: D003470:Culture Media; D005459:Fluorides