Inhibitory effect of sodium fluoride and chlorhexidine on the growth of oral lactobacilli

The accumulation of microorganisms in dental plaque is related to the etiology of caries and periodontal disease, with a high prevalence worldwide. The prophylactic measures include the use of chemical agents as NaF and chlorhexidine. Lactic acid bacteria are members of the normal microbiota of the oral cavity being discussed with regard to their beneficial or detrimental effect in this environment. The present study was performed to determine the growth of some species of Lactobacillus at different concentrations of NaF and chlorhexidine. The strains were isolated from both caries-free and caries patients. Their growth parameters were evaluated by the application of the Gompertz model to the experimental data of optical density as a measurement of growth. The degree of inhibition of the growth of all of the lactobacilli studied was different, depending on each particular strain. NaF at 1 mmol center dot L-1 inhibited between 5% and 46%, at 5 mmol center dot L-1 between 13% and 65%, and at 20 mmol center dot L-1 between 57% and 84%. CHX at higher concentrations (197 and 98 mmol center dot L-1) showed a complete inhibition of some of the strains. The significance of the results was evaluated by the application of a multivariate analysis and also compared with the inhibition of pathogenic Streptococcus mutans and with lactobacilli strains from collection cultures.