Cariogenic Potential of Lactose-Free Infant Formulas: An in Vitro Analysis of Streptococcus mutans Biofilm and Acidogenicity

Abstract

Aim: Lactose-free infant formulas (LFs) are commonly used for children with lactose intolerance, but their potential contribution to early childhood caries (ECC) remains poorly understood, particularly with varying sugar compositions. The present study aimed to assess the biofilm-forming ability, acidogenicity, and structural biofilm characteristics of LFs with and without sucrose using a Streptococcus mutans in vitro model. Materials and Methods: Two LFs (with and without 24% sucrose) were tested alongside brain heart infusion (BHI) (negative control) and BHI + 10% sucrose (positive control). S. mutans biofilm formation was quantified using crystal violet staining (A 590nm). Biofilm pH was measured after 24 h of incubation. Structural characteristics were assessed via confocal laser scanning microscopy (CLSM). Statistical analysis included Kruskal-Wallis tests, Bonferroni post hoc tests, and linear regression modeling (P < 0.05). Results: Both LF samples showed significantly greater biofilm formation than the negative control (A 590nm: 3.57 ± 0.06 vs. 0.08 ± 0.02; P < 0.05). Biofilm pH was significantly lower in both LFs (4.23 and 4.28) than in BHI alone (5.26; P < 0.05). However, there were no significant differences between the LFs with and without sucrose. CLSM revealed denser S. mutans aggregation in sucrose-supplemented LF, but without distinct biofilm boundaries. Conclusion: LFs, even those without supplemental sucrose, promote S. mutans biofilm formation and acidogenicity, suggesting a potential cariogenic risk. These findings underscore the need for careful dietary recommendations and oral hygiene strategies for infants consuming LF formulas. Further studies involving in vivo and clinical trials are warranted to validate the results and assess the long-term implications for ECC development.