Differences in tongue microbiota of older adults with a high fungal load according to tongue coating status

The tongue microbiota of older adults requires careful attention because it can be aspirated into the lower respiratory tract due to impaired swallowing function. This study focused on differences in the tongue microbiota of older adults with a high fungal load, with and without tongue coating. We initially quantified the total fungal load of tongue microbiota in 145 individuals receiving commuting rehabilitation services (mean age, 87.6 ± 6.5 years) using quantitative polymerase chain reaction targeting the fungal ribosomal internal transcribed spacer (ITS) region. The fungal and bacterial compositions of 58 individuals with high fungal loads were determined based on the fungal ITS region and bacterial 16S rRNA gene amplicon sequencing, respectively. No significant differences were observed in the fungal load and composition of the tongue microbiota between individuals with no/slight and substantial tongue coating (Winkel Tongue Coating Index ≤3 and >3, respectively), and Candida albicans was the predominant fungal species of the tongue microbiota regardless of the tongue coating status. In contrast, individuals with no/slight tongue coating exhibited significantly lower bacterial loads and higher relative abundances of acidogenic taxa, including Streptococcus mutans and Lactobacillus gasseri , compared with those with substantial tongue coating. These bacterial communities were also distinct from those of individuals with no/slight tongue coating and a low fungal load. These findings indicate that the reduction in tongue coating accompanied by fungal overgrowth in older adults reflects alterations in the bacterial community, rather than differences in fungal composition.