Variations in oral health outcomes and mycobiome composition among COVID-19 convalescents.

The link between gut microbiota and COVID-19 has been previously established, but the role of the oral fungal microbiota in this context remains underexplored. This study aimed to characterize the oral mycobiome of COVID-19 convalescents. Saliva samples were collected from three groups: COVID-19 patients treated with antibiotics (group I), COVID-19 patients without antimicrobial treatment (group II), and healthy volunteers (group III) from the University Hospital and from the University Dental Clinic in Kraków. The samples were analyzed using next-generation sequencing (NGS) targeting the ITS-1 region. Statistically significant differences in dental indices (Plaque Index-PI, Bleeding on Probing-BOP, Winkel Tongue Coating Index-WTCI) were observed between the convalescent groups (I and II) and the control group (III). At the phylum level, significant alpha diversity differences were noted across all groups. At the genus level, alpha diversity was significant for all tested indices. Beta diversity analysis revealed no significant differences between groups I and II at either the phylum or genus levels (p > 0.05). The most abundant genera were Candida and Malassezia, with Candida being more prevalent in group I (88.11%) compared to group II (78.20%) and group III (45.81%). Linear discriminant analysis (LDA) indicated Candida as overrepresented in group I, and Malassezia as a characteristic marker in group II. Additionally, we observed the higher evenness of mold species like Aspergillus and Penicillium in the control group compared to the COVID-19 convalescents. COVID-19 convalescents, particularly those treated with antibiotics, exhibited worse oral condition compared to healthy controls, with Candida overgrowth strongly associated with antibiotic use.