Synergism of Streptococcus mutans and Candida albicans Reinforces Biofilm Maturation and Acidogenicity in Saliva: An In Vitro Study.

Hye-Eun Kim,Yuan Liu,Marwa Bawazir,Geelsu Hwang,Atul Dhall,Hyun Koo

doi:10.3389/fcimb.2020.623980

Hye-Eun Kim, Yuan Liu + Show 4 more

Open Access

https://doi.org/10.3389/fcimb.2020.623980

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Abstract

Early childhood caries, a virulent-form of dental caries, is painful, difficult, and costly to treat that has been associated with high levels of Streptococcus mutans (Sm) and Candida albicans (Ca) in plaque-biofilms on teeth. These microorganisms appear to develop a symbiotic cross-kingdom interaction that amplifies the virulence of plaque-biofilms. Although biofilm studies reveal synergistic bacterial-fungal association, how these organisms modulate cross-kingdom biofilm formation and enhance its virulence in the presence of saliva remain largely unknown. Here, we compared the properties of Sm and Sm-Ca biofilms cultured in saliva by examining the biofilm structural organization and capability to sustain an acidic pH environment conducive to enamel demineralization. Intriguingly, Sm-Ca biofilm is rapidly matured and maintained acidic pH-values (~4.3), while Sm biofilm development was retarded and failed to create an acidic environment when cultured in saliva. In turn, the human enamel slab surface was severely demineralized by Sm-Ca biofilms, while there was minimal damage to the enamel surface by Sm biofilm. Interestingly, Sm-Ca biofilms exhibited an acidic environment regardless of their hyphal formation ability. Our data reveal the critical role of symbiotic interaction between S. mutans and C. albicans in human saliva in the context of pathogenesis of dental caries, which may explain how the cross-kingdom interaction contributes to enhanced virulence of plaque-biofilm in the oral cavity.

Highlights

A hyper-virulent form of tooth decay, Early Childhood Caries (ECC), is a biofilm-derived oral disease induced by protracted ingestion of dietary sugars (Hallett and O’Rourke, 2002; Parisotto et al, 2010; Hajishengallis et al, 2017)
S. mutans and C. albicans are found from plaque-biofilms in ECC patients
We compared the biofilm properties cultured in saliva contained media (0 to 100%) and investigated how human saliva modulates the acidogenicity and virulence of cariogenic crosskingdom biofilms to mimic physiological conditions in the human mouth

Summary

Introduction

A hyper-virulent form of tooth decay, Early Childhood Caries (ECC), is a biofilm-derived oral disease induced by protracted ingestion of dietary sugars (Hallett and O’Rourke, 2002; Parisotto et al, 2010; Hajishengallis et al, 2017). Previous in vitro and in vivo studies demonstrated the mechanism of bacterial-fungal interaction whereby S. mutansderived exoenzymes, glucosyltransferases B (GtfB), avidly bind to C. albicans and produce extracellular glucans on C. albicans in the presence of sucrose, promoting subsequent S. mutans binding to C. albicans (Gregoire et al, 2011; Falsetta et al, 2014; Hwang et al, 2015; Hwang et al, 2017) This enhanced interaction accelerates microbial carriage and production of exopolysaccharides (EPS), facilitating enamel dissolution on the tooth surface due to their acidogenic and aciduric characteristics in a milieu rich in dietary carbohydrates (Hwang et al, 2017; Xiao et al, 2017; Pereira et al, 2018). Saliva exhibited diverse protective functions against dental caries such as i) facilitating clearing irritants, such as microorganisms and dietary carbohydrates; ii) preventing tooth demineralization via various inorganics (e.g., calcium and phosphorus), buffering acids from dietary carbohydrates and bacterial fermentation byproducts; iii) providing antimicrobial activity through numerous proteins, peptides (e.g., histidine), and antibodies (secretory immunoglobin A) (Hara and Zero, 2014; van’t Hof et al, 2014; Colombo et al, 2016; Pedersen and Belstrøm, 2019)

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