Isofloridoside: a novel inhibitor of Streptococcus mutans biofilm formation and glucosyltransferase activity

Abstract

Objective: Isofloridoside, a galactose-containing heteroside derived from marine red algae, has potential applications as a sweetener because it can activate the sweetness receptors T1R2/T1R3. The purpose of this study was to investigate the effects of isofloridoside on the growth and sucrose-dependent biofilm formation of the cariogenic bacterium Streptococcus mutans, to evaluate its potential as a caries-preventing agent.

Results: The results showed that S. mutans did not grow when isofloridoside was the sole carbon source. Isofloridoside inhibited sucrose-dependent biofilm formation by S. mutans in a concentration-dependent manner, similar to galactose and glucose, but unlike melibiose and galactose-containing disaccharides. Biofilm inhibition induced by isofloridoside was associated with inhibition of glucosyltransferase activity. Isofloridoside exhibited biofilm inhibition comparable to xylitol, an alternative sugar known to inhibit biofilm formation. The differential effects of isofloridoside and melibiose on biofilm formation may result from the structural differences that affect their interactions with S. mutans enzymes. These findings highlight the potential of galactose and its polysaccharides as regulators of S. mutans biofilm formation, and suggest that isofloridoside is a promising alternative sweetener for caries prevention.

Keywords: Streptococcus mutans; Alternative sweetener; Biofilm formation; Dental caries; Galactose; Glucosyltransferase (GTF); Isofloridoside.

Fig. 1

Effects of isofloridoside and other carbohydrates on S. mutans growth. A Turbidity assay. The growth curve of S. mutans UA159 is depicted with squares, circles, triangles, and diamonds representing the control, 1% (w/v), 2.5% (w/v), and 5.0% (w/v) treatments, respectively. The incubation period was either 48 or 34 h. The experiments were conducted independently on three occasions, and data from a representative trial are presented. B Viable cell count assay. The effects of 1% (w/v) isofloridoside on S. mutans UA159, NBRC13955, and nine clinical isolates were assessed using viable cell counts. These counts are expressed as log CFU/mL. Black bars denote the control at the initial time point, whereas gray bars represent 48 h of cultivation. The experiments were independently conducted three times, with error bars indicating the standard deviation. Different letters indicate significant differences based on the standard t-test between two groups (*p < 0.05, ** p < 0.01)

Fig. 2

Effects of isofloridoside and other carbohydrates on S. mutans biofilms. Biofilm levels were quantified as relative values, with the control value standardized at 1. Light gray, dark gray, and black bars represent 1%, 2.5%, and 5% (w/v) addition of isofloridoside and other carbohydrates, respectively. The experiments were independently conducted three times, with error bars indicating the standard deviation. Different letters indicate significant differences based on the standard t-test between two groups (*p < 0.05, ** p < 0.01)

Fig. 3

Effect of isofloridoside and other carbohydrates on S. mutans GTF activity. GTF activity was quantified as a relative value, with the control value standardized to 1. Light gray, dark gray, and black bars represent 1%, 2.5%, and 5% (w/v) addition of isofloridoside and other carbohydrates, respectively. The experiments were independently conducted three times, with error bars indicating the standard deviation. Different letters indicate significant differences based on the standard t-test between two groups (*p < 0.05, ** p < 0.01).