Effect of food preservatives on in situ biofilm formation.
ABSTRACT The aim of this double-blind, controlled crossover study was to evaluate the influence of food preservatives on in situ dental biofilm growth. Twenty-four volunteers wore appliances with six specimens each of bovine enamel to build up intra-oral biofilms. During three test cycles, the subjects had to put one half of the appliance twice a day in one of the assigned active solutions (0.1% benzoate, BA; 0.1% sorbate, SA or 0.2% chlorhexidine, CHX) and the other into NaCl. After 5 days, the developed biofilms were stained with two fluorescent dyes to visualise vital (green) and dead bacteria (red). Biofilms were scanned by confocal laser scanning microscopy and biofilm thickness (BT) and bacterial vitality (BV%) were calculated. After a washout period of 7 days, a new test cycle was started. The use of SA, BA and CHX resulted in a significantly reduced BT and BV compared to NaCl (p<0.001). Differences between SA and BA were not significant (p>0.05) for both parameters, while CHX showed significantly lower values. Both preservatives showed antibacterial and plaque-inhibiting properties, but not to the extent of CHX. The biofilm model enabled the examination of undisturbed oral biofilm formation influenced by antibacterial components under clinical conditions.
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ABSTRACT: The short-term kinetics of fluoride uptake by cells from 20- to 22-h cultures of Streptococcus mutans strain 6715 were studied using rapid filtration and centrifugation techniques. Saline-suspended organisms were diluted with fluoride-containing solutions buffered at four different pH values (2.0, 4.0, 5.5, and 8.2). Fluoride disappearance from the medium was inversely related to pH and to the duration of the exposure at any given pH. The uptake was rapid and extensive at the lower pH values and decreased as the pH increased. Media fluoride concentrations subsequently increased; i.e., fluoride was released from the cells. The presence of glucose, cyanide, or iodoacetate did not influence the results. However, preincubation of the cells in fluoride-free buffers, followed by the addition of fluoride, reduced fluoride uptake markedly. Cell-to-media pH gradients were determined by the distribution of 14C-labeled 5,5-dimethyl-2,4-oxazolidinedione. Fluoride uptake was found to be a function of the magnitude of the pH gradient (P less than 0.001). It is hypothesized that fluoride uptake occurs by the diffusion of hydrogen fluoride and the subsequent trapping of ionic fluoride.Infection and Immunity 01/1978; 18(3):680-7. · 4.07 Impact Factor
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ABSTRACT: The effects of cinnamic, propionic, benzoic and sorbic acids on the growth and intracellular pH of Escherichia coli were investigated. The data suggest that the potency of weak acids as food preservatives is related to their capacity to reduce specifically the intracellular pH. The data also suggest that although both the undissociated forms of the acid cause the intracellular pH to fall, growth inhibition is due predominantly to the undissociated acid.Journal of general microbiology 12/1984; 130(11):2845-50.
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ABSTRACT: Antibiotics are generally not effective against organisms in exopolysaccharide biofilms. A simple method of studying the effect of antibiotics on bacteria in established biofilms is reported. Escherichia coli ATCC 25922 cells grown overnight at 37 degrees C on Mueller-Hinton agar were suspended in buffer and dispensed on 0.5-cm2 catheter disks. The disks were incubated for 1 h at 37 degrees C, washed, transferred to petri dishes containing 20 ml of broth, and incubated at 37 degrees C for 20 to 22 h, at which time thick biofilms were established. Disks were washed, placed in broth or broth containing antibiotic, and incubated at 37 degrees C for 4 h. The disks were removed, and viable counts were determined. This process was repeated at other selected time intervals (e.g., 8 and 24 h). Viable bacterial counts decreased from 10(3) to 10(4) CFU/cm2 in 24 h with 400 micrograms of amdinocillin or cefamandole per ml. A combination containing 400 micrograms of each antibiotic per ml decreased the viable counts to an undetectable level (less than 100 CFU/cm2) in 24 h. Other antibiotics and organisms were also examined in this system.Antimicrobial Agents and Chemotherapy 11/1987; 31(10):1502-6. · 4.57 Impact Factor