Microbiological studies of plaque-biofilms from toddlers reveal a direct association between early-childhood caries (ECC) and the presence of Candida albicans, along with high levels of Streptococcus mutans. Previous in vitro and in vivo studies suggest strongly that S. mutans interactions with C. albicans may influence the pathogenesis of ECC. Using a rodent model of the disease, enhanced levels of infection with elevated carriage of S. mutans and C. albicans were observed in plaque-biofilms from co-infected animals compared to those infected with either species alone. Importantly, the virulence of plaque-biofilm in co-infected animal was dramatically enhanced, leading to the development of rampant carious lesions on smooth-surface of teeth (similar to those found in ECC). Further in vitro studies have identified a cooperative and sucrose-dependent S. mutans-C. albicans interactions that is mediated by S. mutans exoenzymes termed glucosyltransferases (Gtfs). Of the three Gtfs, GtfB binds most avidly to C. albicans cell surface, retains enzymatic activity and produces exopolysaccharides (EPS) on C. albicans surfaces in the presence of sucrose in vitro. The surface-formed EPS enhances adhesive interactions between S. mutans and C. albicans, promotes the assembly of an EPS- rich extracellular matrix, and increases colonization of S. mutans and co-species biofilm formation onto saliva- coated apatitic surfaces. We hypothesize that S.mutans-C.albicans association mediated via GtfB modulates the development of hypercariogenic biofilms on teeth. It is possible that the assembly of EPS- rich matrix and elevated microbial accumulation enhance biofilm mechanical stability/cohesiveness and facilitate the creation of acidic microenvironments within biofilms, which can influence the onset and progression of caries in vivo. To test our hypothesis, we will (Aim 1) characterize the interaction of S. mutans derived-GtfB with C. albicans using genetic approaches (e.g. screening mutants of C. albicans) combined with spectroscopic/fluorescence and AFM methods (for GtfB binding and activity measurements) in vitro. GtfB binding and glucan synthesis by the enzyme on the fungal surface modulates S. mutans-C. albicans co- adherence and co-species biofilm formation. Therefore, we will identify C. albicans mutant strains that are defective in both the GtfB binding and enzymatic activity.
In Aim 2, the effects of this fungal-bacterial interaction via GtfB on biofilm development and mechanical stability will be determined using a new engineering tool, while spatio-temporal development of acidic niches within biofilms will be assessed using time-lapsed pH mapping in vitro. Lastly, in Aim 3, we will examine the role of GtfB-mediated S. mutans-C. albicans interaction in the pathogenesis of the disease in vivo using GtfB-binding/activity defective C. albicans or gtfB-defective S. mutans (along with their parental strains) with our rodent model. A comprehensive program from laboratory studies to in vivo investigations is offered to provide critical insights into the mechanisms of this S. mutans-C albicans interaction and its implications in enhancing the virulence of dental caries disease.

Public Health Relevance

The association between Streptococcus mutans and Candida albicans modulates the development of hypercariogenic biofilms that may be relevant in the context of early childhood caries (ECC), one of the most painful and costly infectious diseases afflicting toddlers. S. mutans-derived exoenzyme (GtfB) appears to be an essential factor for this unique and highly virulent cross-kingdom interaction. We propose to further understand how GtfB mediates S. mutans-C. albicans association and the expression of biofilm virulence in vivo.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Small Research Grants (R03)
Project #
1R03DE025728-01
Application #
9016967
Study Section
NIDCR Special Grants Review Committee (DSR)
Program Officer
Rodriguez-Chavez, Isaac R
Project Start
2016-01-01
Project End
2017-12-31
Budget Start
2016-01-01
Budget End
2016-12-31
Support Year
1
Fiscal Year
2016
Total Cost
$80,000
Indirect Cost
$30,000
Name
University of Pennsylvania
Department
Dentistry
Type
Schools of Dentistry
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Xiao, Jin; Hara, Anderson T; Kim, Dongyeop et al. (2017) Biofilm three-dimensional architecture influences in situ pH distribution pattern on the human enamel surface. Int J Oral Sci 9:74-79
Hwang, Geelsu; Liu, Yuan; Kim, Dongyeop et al. (2017) Candida albicans mannans mediate Streptococcus mutans exoenzyme GtfB binding to modulate cross-kingdom biofilm development in vivo. PLoS Pathog 13:e1006407
Hwang, Geelsu; Liu, Yuan; Kim, Dongyeop et al. (2016) Simultaneous spatiotemporal mapping of in situ pH and bacterial activity within an intact 3D microcolony structure. Sci Rep 6:32841