Candida species and oral mycobiota of patients clinically diagnosed with oral thrush

Abstract

Overgrowth of Candida yeasts in the oral cavity may result in the development of oral thrush in immunocompromised individuals. This study analyzed the diversity and richness of the oral mycobiota of patients clinically diagnosed with oral thrush (OT), follow-up of oral thrush patients after antifungal therapy (AT), and healthy controls (HC). Oral rinse and oral swab samples were collected from 38 OT patients, 21 AT patients, and 41 healthy individuals (HC). Pellet from the oral rinse and oral swab were used for the isolation of oral Candida yeasts on Brilliance Candida Agar followed by molecular speciation. ITS1 amplicon sequencing using Illumina MiSeq was performed on DNA extracted from the oral rinse pellet of 16 OT, 7 AT, and 7 HC oral rinse samples. Trimmed sequence data were taxonomically grouped and analyzed using the CLC Microbial Genomics Module workflow. Candida yeasts were isolated at significantly higher rates from oral rinse and swab samples of OT (68.4%, p < 0.001) and AT (61.9%, p = 0.012) patients, as compared to HC (26.8%). Predominance of Candida albicans specifically, was noted in OT (60.5%, p < 0.001) and AT (42.9%, p = 0.006) vs. HC (9.8%), while non-albicans Candida species was dominant in HC. Analysis of oral mycobiota from OT patients showed the presence of 8 phyla, 222 genera, and 309 fungal species. Low alpha diversity (Shannon index, p = 0.006; Chao-1 biased corrected index, p = 0.01), varied beta diversity (Bray-Curtis, p = 0.01986; Jaccard, p = 0.02766; Weighted UniFrac, p = 0.00528), and increased relative abundance of C. albicans (p = 3.18E-02) was significantly associated with the oral mycobiota of OT vs. HC. This study supported that C. albicans is the main etiological agent in oral thrush and highlights the association of fungal biodiversity with the pathophysiology of oral thrush.

Fig 1. Box plots depicting alpha diversity measures for each study group (AT, HC, and OT).

(a) Shannon entropy and (b) Chao-1 biased corrected analysis. The different colors represent the oral thrush status of participants.

Fig 2. Beta diversity (Bray-Curtis) PCoA plots.

The graph highlights the relationship between (a) OT, HC, and AT study groups. Pco1 (16%) and Pco2 (43%) examined the difference in oral mycobiota composition between oral rinse samples, with significant clustering evident in OT vs. HC participants (p = 0.02). Clinical variables such as (b) age, (c) sex, and (d) ethnicity were analyzed for OT patients, with no significant differences observed (p ≥ 0.05).

Fig 3. Venn diagram illustrating the number of shared and distinct species in the oral mycobiota of oral thrush, healthy control, and follow-up participant oral rinse samples.

Fig 4. Relative abundance of the top 10 fungal species according to study group (arranged from highest to lowest species relative abundance in OT patients).

Fig 5. Significant differential abundance (p < 0.05) of fungal taxa within group pairs.

a) OT vs. HC (Top 25 strains that showed significant downregulation in OT patients), b) AT vs. HC (A total of 20 strains showed significant upregulation in AT patients, while 1 species showed significant downregulation), c) AT vs. OT (Top 25 strains that showed significant upregulation in AT patients, while only 2 strains showed significant downregulation).