Interactions between non-albicans Candida and Streptococcus mutans enhance cariogenic potential of dual-species interkingdom biofilms.

Background: Non-albicans Candida species (NACs) are commonly found in carious lesions, yet their specific role in caries progression remains unclear. Hence, we conducted an in vitro study to explore how NACs interactions with Streptococcus mutans affect cariogenicity.

Materials and methods: Dual-species interkingdom biofilms were developed with S.mutans and six Candida species, C.albicans and the NACs: C.dubliniensis, C.glabrata, C.krusei, C.parapsilosis and C.tropicalis. Biofilm mass, viable cell counts, and pH were evaluated in mono- and dual-species biofilms. Quantitative RT-PCR was used to assess the expression of S.mutans genes associated with cariogenicity.

Results: Co-culturing S.mutans with either C.albicans, C.glabrata, or C.tropicalis significantly increased biofilm mass. While S.mutans numbers either increased or remained stable in dual-species biofilms, C.krusei, C.parapsilosis, and in particular C.tropicalis numbers significantly increased. All dual-species biofilms exhibited a pH below the critical demineralization level of enamel, akin to S.mutans mono-species biofilms. The expression of a battery of cariogenic genes in S.mutans was upregulated, particularly in dual-species biofilms with C.krusei and with C.tropicalis.

Conclusion: NACs influence the biofilm production and the cariogenic gene expression of S.mutans. The dual-species biofilm of S.mutans and NACs, particularly C.tropicalis, likely possess heightened cariogenic potential. Further research is warranted to unravel these intriguing interactions within interkingdom biofilms.