Characteristics of oral microbiota alterations in COVID-19: a literature review

Relevance. This review examines current evidence on COVID-19–related changes in the oral microbiota. SARS-CoV-2 may affect the composition of the oral microbial community, contributing to dysbiosis and the development of inflammatory changes. Accordingly, alterations in the oral microbiome may serve as potential biomarkers of susceptibility to infection and disease severity. Previous studies have shown that patients who have recovered from COVID-19 exhibit a significant reduction in salivary secretory immunoglobulin A (IgA) levels compared with individuals without a history of the disease. These findings highlight the need for further investigation into the impact of coronavirus infection on oral microecology and for the development of appropriate clinical recommendations.

Materials and methods. A systematic literature search was performed in the PubMed, Scopus, Web of Science, eLIBRARY.ru, and Google Scholar databases using Russianand English-language keywords, including “microflora”, “oral cavity”, “COVID”, “coronavirus”, “oral microbiota”, and “COVID-19”. The review covered publications from 2002 to 2024, with particular emphasis on studies published since the onset of the COVID-19 pandemic in 2020 that focused on xerostomia and oral diseases. Additional manual searches were conducted in relevant journals and reference lists. Study selection and data analysis were carried out in accordance with PRISMA guidelines. Original research articles, narrative reviews, and meta-analyses with full-text availability and clearly described methodologies were included, provided they examined the role of the oral microbiota in COVID-19 and its clinical manifestations. Studies without data on oral microbiota, unrelated to COVID-19, lacking full-text access, or containing duplicate data were excluded.

Results. Recent studies indicate that COVID-19 is is associated with oral pathological changes and disruption of the oral microbiota. An increase in opportunistic microorganisms, including Streptococcus, Prevotella, and Aggregatibacter, has been reported, alongside a reduction in beneficial microbial species. Alterations have also been observed in the fungal component of the microbiome, with decreased abundance of Candida and Saccharomyces spp. ertain microorganisms, such as Fusobacterium nucleatum, may exacerbate disease severity by increasing ACE2 expression and promoting inflammatory responses. COVID-19–related changes in the oral microbiota and oral mucosal tissues not only compromise oral health but may also contribute to greater disease severity. In this context, oral microorganisms are increasingly regarded as potential biomarkers for infection diagnosis and monitoring.

Conclusion. Alterations in the oral microbiota are not considered primary manifestations of COVID-19 and are largely attributable to medication-related effects. Nevertheless, COVID-19 can modify salivary composition and disrupt the oral microbiome, potentially contributing to the development of oral diseases and influencing disease progression. Certain bacterial species may enhance infection (e.g., Fusobacterium nucleatum), whereas others may exhibit inhibitory effects (e.g., Porphyromonas gingivalis). Overall, the oral microbiome may serve both as an indicator of COVID-19 severity and as an active participant in its pathogenesis. 

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