A New Small Molecule Specifically Inhibits the Cariogenic Bacterium Streptococcus mutans in Multispecies Biofilms

Abstract

Streptococcus mutans is a major cariogenic bacterium. It has adapted to the biofilm lifestyle, which is essential for pathogenesis of dental caries. We aimed to identify small molecules that can inhibit cariogenic S. mutans and to discover lead structures that could give rise to therapeutics for dental caries. In this study, we screened a focused small-molecule library of 506 compounds. Eight small molecules which inhibited S. mutans at a concentration of 4 M or less but did not affect cell growth or biofilm formation of commensal bacteria, represented by Streptococcus sanguinis and Streptococcus gordonii, in monospecies biofilms were identified. The active compounds share similar structural properties, which are characterized by a 2-aminoimidazole (2-AI) or 2-aminobenzimidazole (2-ABI) subunit. In multispecies biofilm models, the most active compound also inhibited cell survival and biofilm formation of S. mutans but did not affect commensal streptococci. This inhibitor downregulated the expression of six biofilm-associated genes, ftf, pac, relA, comDE, gbpB, and gtfB, in planktonic S. mutans cells, while it downregulated the expression of only ftf, pac, and relA in the biofilm cells of S. mutans. The most potent compound also inhibited production of two key adhesins of S. mutans, antigen I/II and glucosyltransferase (GTF). However, the compound did not alter the expression of the corresponding genes in both S. sanguinis and S. gordonii, indicating that it possesses a selective inhibitory activity against S. mutans.Bacterial biofilms are defined as surface-attached bacterial communities encased in an extracellular matrix of polysaccharides, proteins, and DNA. About 75% of infectious diseases are associated with biofilms (4). As sessile bacteria grown in biofilms inherently withstand host immune responses and are more resistant to antibiotics, biocides, and hydrodynamic shear forces than their planktonic counterparts, there is a significant hurdle to overcome in treating biofilm-mediated infections (30). Therefore, there is an urgent need to develop new and effective therapeutics for biofilm-associated diseases.Dental caries is one of the most common infectious diseases in humans and is initiated by the formation of dental plaque biofilms. Although different bacteria have been found to be associated with pathogenesis of dental caries, the mutans streptococcal group represented by Streptococcus mutans is considered to be a major etiologic agent in the pathogenesis of dental caries. Currently, dental plaque is eradicated mainly through nonspecific mechanical removal or treatment with broad-spectrum antibiotics. In addition, a number of derivatives from natural products, such as cranberry constituents, plant lectins, crude extracts of Morus alba leaves, and fractions of barley coffee, have been shown to be effective against biofilm formation of S. mutans. These substances can regulate the activities of surface-anchored virulence factors glucosyltransferase and fructosyltransferase (5,7,9,14,34). Numerous small mole...

Inhibition of Streptococcus mutans biofilm formation, extracellular polysaccharide production, and virulence by an oxazole derivative

“…However, brushing and flossing are neither practical nor accessible for many individuals, as they lack the knowledge, skills, or motivation (Cummins 2013). On the other hand, the consistent use of broad-spectrum antibiotics, which kill or inhibit the growth of planktonic bacteria, may disturb the body's microflora and lead to severe infections (Liu et al 2011).…”

Molecule Targeting Glucosyltransferase Inhibits Streptococcus mutans Biofilm Formation and Virulence

“…However, few of these treatments have been proven to confer selectivity against S. mutans biofilms. In recent years, targeted antimicrobials capable of selectively eliminating S. mutans have been designed to achieve targeted killing with a minimal effect on other oral microbes (18)(19)(20), opening up alternative methods to prevent caries without disturbing the ecological balance between pathogens and commensal bacteria in the oral cavity.…”

Effect of Sodium Fluoride, Ampicillin, and Chlorhexidine on Streptococcus mutans Biofilm Detachment

“…Several studies have indicated that the extent of Candida albicans biofilm detachment and detached-cell viability are dependent on the types of antimicrobials employed (26) and that detached cells gain enhanced adherence abilities (25). Given the breadth of the detrimental effects caused by biofilms and biofilm-detached cells, there have been significant efforts to develop and find agents controlling biofilm detachment and decreasing pathogenicity and viability of biofilm-detached cells (11,15).…”

“…In addition, the effect of the antimicrobials on S. mutans biofilm structures was assessed using confocal laser scanning microscopy (CLSM) (15,17). Biofilm thickness and live/dead cell ratios were calculated using COMSTAT software.…”