title: Reduction in acid tolerance of Streptococcus downeii by fluoride and potassium laurate.
abstract: Streptococcus downeii MFe28 maintains a transmembrane pH gradient at low extracellular pH values using energy from glucose metabolism. The metabolic activity was measured in saturating glucose solutions using a pH-stat, and results were expressed as rates of titratable acid production at defined pH values. The tolerance to acid shock was studied in terms of the ability of cells to resume acid production at pH 8.0 following short-term exposure to low-pH environments. The results with control cells showed an optimum rate of acid production at pH 8.0. The activity extended to pH 4.5 with a half-maximal rate at pH 5.4. Addition of carbonyl cyanide-m-chlorophenylhydrazone, potassium laurate, or potassium fluoride inhibited acid production at lower but not at higher pH values. Inhibition by carbonyl cyanide-m-chlorophenylhydrazone and fluoride was found to be fully reversible at pH 8.0 when compared to control cells. In contrast, laurate inhibited irreversibly at pH values of 6.0 and below. The acid tolerance of S. downeii was severely compromised by laurate, and this action could be useful in dental caries control.
authors.affiliation: Department of Biochemistry, School of Medical Sciences, Bristol, UK.
authors.forename: M L
authors.initials: ML
authors.lastname: Hayes
mesh_terms: D000143:Acids / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007850:Lauric Acids / Q000494:pharmacology*; D013291:Streptococcus / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D000143:Acids; D001426:Bacterial Proteins; D007850:Lauric Acids; C030358:lauric acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D005947:Glucose; D005459:Fluorides