Yilan Miao
| Yilan Miao |
Yilan Miao1, Rodrigo A Arthur2, Thais C Negrini3, Ren Zhi
Hyun (Michel) Koo1
1Orthodontics, University of Pennsylvania, School of Dental Medicine; 2Preventive and Community Dentistry Department, Federal University of Rio Grande do Sul; 3Department of Clinical Analysis, São Paulo State University
Introduction
Bacterial-fungal interactions between Candida albicans and Streptococcus mutans are frequently detected in saliva from children with severe early childhood caries. However, how they interact in saliva to initiate cariogenic biofilms under cariogenic conditions remains unclear. We hypothesize that dietary sugars can induce cross-kingdom coaggregation in saliva which further colonizes the tooth surface and initiate biofilms.
Methods
We developed a saliva-based coaggregation model using S. mutans UA159 and C. albicans SC5314. Clarified pooled human saliva from healthy individuals was supplemented with different dietary sugars including glucose/fructose, sucrose, starch, and their combinations. A mixture of planktonic S. mutans and C. albicans was incubated (37°C, 60 min) to induce coaggregation. Then, a vertically-positioned saliva-coated hydroxyapatite disc (tooth-enamel surrogate) was introduced to allow microbial binding. The disk was transferred into fresh culture medium with the same sugar as in the coaggregation. The initial binding community and biofilms were imaged using confocal microscopy and images were computationally analyzed to determine surface coverage and biovolume. Microbiological/biochemical analysis were conducted to assess viable cells in biofilms and their acidogenicity.
Results
We found that S. mutans and C. albicans could form cross-kingdom coaggregates in saliva. The coaggregation was facilitated by sucrose, forming highly complex multicellular fungal-bacterial superstructure emmeshed by extracellular polysaccharides. The preformed coaggregates could bind to the surface as a unit and initiate biofilms. In the presence of sucrose, the coaggregate-derived biofilms showed the highest surface coverage at initial binding and the largest biofilm volume formed at 19h (p<0.05). Furthermore, coaggregate-derived biofilms formed in sucrose contained the highest dry weight and the most bacterial and fungal CFU, while actively producing acids to lower the pH more rapidly than those formed in other sugars (p<0.05).
Conclusion
Our data suggest that sucrose in saliva can significantly induce cross-kingdom coaggregate formation to colonize the surface and initiate cariogenic biofilms implicated with human tooth-decay.