AUTHOR=Sun Yan , Chen Yanhan , Du Qian , Zhang Jin , Xu Muxin , Zheng Gaozhe , Zhou Wen , Zhou Xinxuan , Qiu Lili , Pan Yihuai , Zhang Keke 

TITLE=Fluoride-resistant Streptococcus mutans within cross-kingdom biofilms support Candida albicans growth under fluoride and attenuate the in vitro anti-caries effect of fluorine

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1399525

DOI=10.3389/fmicb.2024.1399525

ISSN=1664-302X

ABSTRACT=<p>Fluoride-resistant <italic>Streptococcus mutans</italic> (<italic>S. mutans</italic>) might affect the ecological balance of biofilms in the presence of fluoride. We used a <italic>S. mutans</italic> and <italic>Candida albicans</italic> (<italic>C. albicans</italic>) cross-kingdom biofilm model to investigate whether fluoride-resistant <italic>S. mutans</italic> in biofilms would support <italic>C. albicans</italic> growth under fluoride stress and attenuate the <italic>in vitro</italic> anti-caries effect of fluorine. The impact of fluoride-resistant <italic>S. mutans</italic> on formation of cross-kingdom biofilms by <italic>S. mutans</italic> and <italic>C. albicans</italic> in the presence of fluoride was investigated <italic>in vitro</italic> using the crystal violet staining assay. Biofilm constitution was determined using colony-forming unit (CFU) counts and fluorescent <italic>in situ</italic> hybridization (FISH). Extracellular polysaccharide (EPS) generation in biofilms was determined by EPS/bacterial dying and water-insoluble polysaccharide detection. Acid production and demineralization were monitored using pH, lactic acid content, and transversal microradiography (TMR). The gene expression of microorganisms in the cross-kingdom biofilm was measured using qRT-PCR. Our results showed that both <italic>C. albicans</italic> and fluoride-resistant <italic>S. mutans</italic> grew vigorously, forming robust cross-kingdom biofilms, even in the presence of sodium fluoride (NaF). Moreover, fluoride-resistant <italic>S. mutans</italic>-containing cross-kingdom biofilms had considerable cariogenic potential for EPS synthesis, acid production, and demineralization ability in the presence of NaF than fluoride-sensitive <italic>S. mutans</italic>-containing biofilms. Furthermore, the gene expression of microorganisms in the two cross-kingdom biofilms changed dissimilarly in the presence of NaF. In summary, fluoride-resistant <italic>S. mutans</italic> in cross-kingdom biofilms supported <italic>C. albicans</italic> growth under fluoride and might attenuate the anti-caries potential of fluorine by maintaining robust cross-kingdom biofilm formation and cariogenic virulence expression <italic>in vitro</italic> in the presence of NaF.</p>