Influence of the use of complete denture adhesives on microbial adhesion and biofilm formation by single- and mixed-species

OBJECTIVES: To verify whether the Ultra Corega Cream and Corega Strip Denture Adhesive adhesives interfere in the microbial adhesion and biofilm formation by Candida albicans and Lactobacillus casei in single- and mixed-species settings, and observe whether synergistic or antagonistic relationships between these species occur. METHODS: Specimens made from heat-polymerized acrylic resin (Lucitone 550) were fabricated (n = 144) with a circular shape and standardized roughness (3.0 μm ±0.3 Ra) and were divided into three groups: Without Adhesive (WA), with Ultra Corega Cream adhesive (CA) and Corega Strips adhesive (SA). These groups were divided into three subgroups each: C. albicans single-species, L. casei single-species and C. albicans with L. casei (mixed-species). Microbial adhesion and biofilm formation assays were performed in duplicate at four distinct experimental times (n = 8 per experimental condition). The amount of each microorganism on the surfaces of the specimens was observed by counting of the Colony Forming Units (CFU) per substrate. Additional specimens were characterized by Scanning Electron Microscopy (SEM), with 18 specimens being used in this analysis (n = 18), 2 per experimental condition (n = 2). Two-way ANOVA and Tukey’s test for multiple comparisons were employed, using α≤0.05. RESULTS: L. casei (mixed-species) adhered more on the WA substrate than the CA, while C. albicans (single- and mixed-species) adhered more on the SA. C. albicans, both single- and mixed-species adhered more than the L. casei (single- and mixed-species), regardless of the substrate. L. casei (single-species) formed more biofilm on the WA, but in its mixed cultivation, it had no difference of growth among the tested situations. C. albicans (single- and mixed-species) formed more biofilm on the SA than the CA, and the fungus formed more biofilm when compared to L. casei. In general, whenever a species was compared in its single- and mixed-species situation, no statistically significant difference was observed. SEM of biofilm formation assays demonstrated that L. casei single-species WA formed more biofilm than when the adhesives tested were used, and C. albicans (both single- and mixed-species) formed more biofilm on the SA than on the CA. CONCLUSIONS: (1) The two denture adhesives tested increased the adhesion of C. albicans but not of L. casei; (2) biofilm formation by C. albicans (single- and mixed-species) was increased on the SA; (3) Relations of synergism or antagonism was not observed between the two microorganisms studied.