INHIBITION OF STREPTOCOCCUS-MUTANS ADSORPTION TO HYDROXYAPATITE BY LOW-MOLECULAR-WEIGHT CHITOSANS

The role of Streptococcus mutans in the initiation of dental caries ha s been recognized and attributed, at least in part, to its ability to colonize the tooth surface. Therefore, factors which prevent S. mutans attachment to hydroxy-apatite (HA) are of considerable interest for t he prophylaxis of this infectious disease. Chitosan, a chitin derivati ve by N-deacetylation, is an interesting candidate in this respect, si nce it stimulates the ordered regeneration of oral soft tissues, preve nts the deleterious action of organic acid, and exhibits bactericidal action against several pathogens. Ln the present work, the efficacy of a low-molecular-weight chitosan (LMWC) and its derivatives N-carboxym ethyl chitosan (NCMC) and imidazolyl chitosan (IMIC) in preventing S. mutans attachment to HA beads was assessed. The effects of chitosan on both sucrose-dependent and -independent adherence were evaluated. In both cases, when saliva-coated or uncoated HA beads were treated with any of the chitosans, a reduction in S. mutans adsorption ranging from 47 to 66% was observed. When HA beads were coated with saliva after t he treatment with chitosan, neither carbohydrate caused a statisticall y significant reduction in S. mutans adsorption, suggesting that saliv a deposition restores HA binding properties. Bacteria grown in the pre sence of chitosan subminimal inhibitory concentrations (sub-MICs) rang ing from 12 to 500 mu g mL(-1) adsorbed poorly to HA and exhibited a l ower affinity toward xylene than untreated controls. In the presence o f chitosan sub-MICs up to 60 mu g mL(-1), an increase in the percentag e of detached bacteria from two- to nine-fold was observed. The desorp tive effect of chitosan was weaker when S. mutans had adhered to saliv a-coated HA in the presence of sucrose. These results demonstrate that the presence of minor amounts of modified chitosans prevents S. mutan s adsorption to HA and suggest that colonization of the tooth surface might be impaired by the use of toothpastes, mouthrinses, or chewing g ums containing any of the tested polysaccharides.