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Table of Contents
Year : 2021  |  Volume : 9  |  Issue : 1  |  Page : 1-3

Role of oral microbiome in the SARS-COV-2 pandemic

Department of Oral Medicine and Radiology, KM Shah Dental College and Hospital, Sumandeep Vidyapeeth Deemed to be University, Vadodara, Gujarat, India

Date of Submission06-Jun-2021
Date of Decision08-Jun-2021
Date of Acceptance10-Jun-2021
Date of Web Publication17-Aug-2021

Correspondence Address:
Dr. Deepa Jatti Patil
Department of Oral Medicine and Radiology, KM Shah Dental College and Hospital, Sumandeep Vidyapeeth Deemed to be University, Vadodara, Gujarat
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jihs.jihs_16_21

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How to cite this article:
Patil DJ. Role of oral microbiome in the SARS-COV-2 pandemic. J Integr Health Sci 2021;9:1-3

How to cite this URL:
Patil DJ. Role of oral microbiome in the SARS-COV-2 pandemic. J Integr Health Sci [serial online] 2021 [cited 2023 Jun 2];9:1-3. Available from: https://www.jihs.in/text.asp?2021/9/1/1/323950

The coronavirus disease 2019 (COVID-19) pandemic presently posing as a global threat has prompted extraordinary research efforts to learn more about SARS-CoV-2 infection, transmission, and early detection.[1] The second wave of the pandemic has seen many co-infections re-emerging and influencing the clinical outcomes and mortality in these patients. During the earlier pandemics, patients with respiratory viral infections were more likely to develop co-infections, which lead to increased disease severity and mortality. However, the literature is scarce regarding this data.[2] In this article, we will have a brief overview of how the oral cavity can be source of SARS-CoV-2 reinfection and its influence on the oral, lung, and gut microbiome.

  Co-infections: a Potentially Fatal and Understudied Aspect of Coronavirus Disease 2019 Top

In the current COVID-19 pandemic, Zhou et al.[3] found that 50% of COVID-19 patients who died had secondary bacterial infections, and Chen et al.[4] found both bacterial and fungal co-infections. The use of antibiotics in SARS-COV-2 infections and prolonged use of mechanical ventilation has increased the risk of co-infections and antimicrobial resistance in these patients. Longitudinal metagenomic studies should be undertaken to understand the pathogenesis of co-infections and antimicrobial resistance.[5]

The importance of oral bacteria in enabling COVID-19 co-infections is often underestimated. The oral microbiome is the collective genome of the bacteria that live in the mouth. Of all the microbiomes in the human body, the oral microbiome is the second largest and most complicated. Bacteria, viruses, protozoa, and fungi constitute the oral microbiome.[6] Microbes inhabit the hard surfaces of teeth and the soft tissues of the oral mucosa in the mouth's many niches, making it an extraordinarily complex ecosystem. The oral microbiome is important for not only oral homeostasis but also sustaining the systemic health in addition to being the starting point for digestion. In spite of this, the potential of the oral cavity and microbiome in the SARS-CoV-2 infection processes and their influence on oral and systemic health has been overlooked.[6]

  SARS-COV-2 Reservoirs in the Oral Cavity Top

The presence of SARS-CoV-2 in the saliva and the presence of oral tissues enriched with angiotensin-converting enzyme 2 (ACE2) receptors suggest that the oral cavity could be a major SARS-CoV-2 reservoir. The virulence of SARS-CoV-2 depends on the ability of ACE2 receptor interacting with the viral spike protein. Various studies and transcriptome analysis have shown the abundance of ACE2 receptors in the salivary glands, tongue, and gingival sulcus. This can be substantiated by the increased expression of ACE2 in the salivary epithelial cells. There have been cases of sialadenitis in SARS-CoV-2-infected patients, especially in the later stages. SARS-CoV-2 has been detected in the saliva of infected patients in the convalescent phase and has been regarded as a source of spread in asymptomatic patients.[7],[8] The gustatory dysfunction observed in the SARS-CoV-2-infected patients may be linked to a greater level of ACE2 expression in tongue epithelial cells.[9] The gingival sulcus is a niche for several bacteria and viruses. Furthermore, gingival crevicular fluid is thought to contain SARS-CoV-2, which is discharged from infected periodontal cells or terminal capillary complexes in periodontal tissues and then mixed with saliva to enter the oral cavity.[10]

  Oral-Lung-Gut Microbiome Top

Viral infection, such as SARS-CoV-2, could disrupt the local microbiome, resulting in dysbiotic communities. Poor oral hygiene is thought to be a primary ecological stressor that causes dysbiosis in complex microbial populations in the mouth. Previous research on the oropharyngeal microbiota of pneumonia patients discovered that the number of Pseudomonas and Bacillus species increased significantly after influenza virus infection, while the number of Prevotella, Veillonella, and Neisseria species decreased significantly.[11] High readings of cariogenic and periodontopathic bacteria have been found in metagenomic investigations of individuals infected with SARS-COV-2, confirming the theory of a link between the oral microbiome and COVID-19 symptoms. Periodontopathic bacteria may play a role in the etiology of respiratory disorders like COVID-19 and are related to chronic inflammatory systemic disorders such as type 2 diabetes, hypertension, and cardiovascular disease, which have been linked to a higher risk of severe COVID-19 consequences and death.[12]

The host's homeostasis, as well as the microenvironment and nutritional availability, are all affected by oral dysbiosis, which changes the hosts susceptibility to infection. The dysbiosis of the oral microbiome can alter the lung and gut microbiome, mainly due to the anatomic similarities and common bacterial species found among them.[7] Periodontal infections and the immune response in periodontitis, for example, have lately been linked to the development of gut inflammation. Furthermore, poor oral health and the buildup of harmful bacteria have been linked to respiratory disorders such as pneumonia, with oral species observed in COVID-19 patients' lung microbiome.[13]

There is an increasing evidence of increase in the amount of opportunistic bacterial and fungal pathogens and decrease in the beneficial symbionts in the intestinal microbiome of COVID-19 patients.[14] The lung microbiome is comprised of oral and nasal microorganisms. The oral cavity serves as a microbiological entry point for bacteria into the lower respiratory system. Poor oral hygiene, which leads to oral microbial dysbiosis, has also been shown to hasten lung function decrease and raise the risk of lung cancer and the number of cases of pneumonia. The aspiration of oral pathogens into respiratory organs, the alteration of the respiratory epithelium by periodontal-associated cytokines, and the rendering of oral mucosal surfaces to promote the adhesion of respiratory pathogens are all proposed mechanisms that could explain the role of oral bacteria in the pathogenesis of respiratory infections. Conversely, oral dysbiosis has been observed in lung transplant patients. This bidirectional relationship could be important in COVID-19 since opportunistic bacteria present in the mouth, including Prevotella, Veillonella, and Capnocytophaga, have been detected in the lungs of SARS-CoV-2 patients.[15]

  Oral and Gut Microbiome as a Predictor for Coronavirus Disease 2019 Severity Top

Another important aspect studied by a group of authors is exploring factors which can predict the severity of COVID-19 infections. The researchers used computational and analytical methods to build a solid foundation for tracing the networks of relationships between the microbiota, clinical characteristics, and disease severity. They discovered that Enterococcus, a type of oral and intestinal bacteria, may accurately predict a patient's death. The gut and oral microbiota are 96% accurate in predicting the COVID-19 severity. Bacteroides uniformis, Enterococcus faecalis, and Monoglobus pectinilyticus were the top three bacterial species for predicting COVID-19 severity in the intestinal microbiome, while Porphyromonas endodontalis, Veillonella tobetsuensis, and Bifidobacterium breve were the top three in the oral microbiome.[16]

We summarized the current evidence and offered an outline for understanding the impact of SARS-CoV-2 infection on the oral microbiota and its relationship to the lung and gut microbiomes. The oral cavity harbors hundreds of microorganisms and can impact the SARS-CoV-2 infection. Future studies should be undertaken to understand oral dysbiosis and SARS-CoV-2 infection. For the characterization of COVID-19 co-infections and the potential link between the involvement of the oral microbiota and virus consequences, more metagenomic investigations and clinical trials are needed. Patients should be throughout the pandemic, the promotion of good oral hygiene as a preventive public health intervention should be emphasized, and future clinical trials should be conducted to ascertain the role of poor oral hygiene as a risk factor in assessing the severity and outcome of SARS-CoV-2 infection.

  References Top

Carvalho T. COVID-19 research in brief: December, 2019 to June, 2020. Nat Med 2020;26:1152-3.  Back to cited text no. 1
Cox MJ, Loman N, Bogaert D, O'Grady J. Co-infections: Potentially lethal and unexplored in COVID-19. Lancet Microbe 2020;1:e11.  Back to cited text no. 2
Zhou F, Yu T, Du R, Fan G, Liu Y, Liu Z, et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: A retrospective cohort study. Lancet 2020;395:1054-62.  Back to cited text no. 3
Chen N, Zhou M, Dong X, Qu J, Gong F, Han Y, et al. Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: A descriptive study. Lancet 2020;395:507-13.  Back to cited text no. 4
Charalampous T, Kay GL, Richardson H, Aydin A, Baldan R, Jeanes C, et al. Nanopore metagenomics enables rapid clinical diagnosis of bacterial lower respiratory infection. Nat Biotechnol 2019;37:783-92.  Back to cited text no. 5
Deo PN, Deshmukh R. Oral microbiome: Unveiling the fundamentals. J Oral Maxillofac Pathol 2019;23:122-8.  Back to cited text no. 6
[PUBMED]  [Full text]  
Xiang Z, Koo H, Chen Q, Zhou X, Liu Y, Simon-Soro A. Potential implications of SARS-CoV-2 oral infection in the host microbiota. J Oral Microbiol. 2020;13:1853451.  Back to cited text no. 7
Xu J, Li Y, Gan F, Du Y, Yao Y. Salivary glands: Potential reservoirs for COVID-19 asymptomatic infection. J Dent Res 2020;99:989.  Back to cited text no. 8
Lechien JR, Chiesa-Estomba CM, Hans S, Barillari MR, Jouffe L, Saussez S. Loss of smell and taste in 2013 European patients with mild to moderate COVID-19. Ann Intern Med 2020;173:672-5.  Back to cited text no. 9
Gomes-Filho IS, Cruz SSD, Trindade SC, Passos-Soares JS, Carvalho-Filho PC, Figueiredo ACMG, et al. Periodontitis and respiratory diseases: A systematic review with meta-analysis. Oral Dis 2020;26:439-46.  Back to cited text no. 10
Leung RK, Zhou JW, Guan W, Li SK, Yang ZF, Tsui SK. Modulation of potential respiratory pathogens by pH 1N1 viral infection. Clin Microbiol Infect 2013;19:930-5.  Back to cited text no. 11
Chakraborty S. Metagenome of SARS-Cov2 patients in Shenzhen with travel to Wuhan shows a wide range of species-Lautropia, Cutibacterium, Haemophilus being most abundant and Campylobacter explaining diarrhea. Open Science Framework. 2020. DOI:10.31219/osf.io/jegwq.  Back to cited text no. 12
Yu G, Gail MH, Consonni D, Carugno M, Humphrys M, Pesatori AC, et al. Characterizing human lung tissue microbiota and its relationship to epidemiological and clinical features. Genome Biol 2016;17:163.  Back to cited text no. 13
Round JL, Mazmanian SK. The gut microbiota shapes intestinal immune responses during health and disease. Nat Rev Immunol 2009;9:313-23.  Back to cited text no. 14
Gaeckle NT, Pragman AA, Pendleton KM, Baldomero AK, Criner GJ. The oral-lung axis: The impact of oral health on lung health. Respir Care 2020;65:1211-20.  Back to cited text no. 15
Ward DV, Bhattarai S, Rojas-Correa M,Purkayastha A, Holler D, Da Qu M et al. The intestinal and oral microbiomes are robust predictors of covid19 severity the main predictor of covid19 related fatality. medRxiv 2021 [doi.org/10.1101/2021.0].  Back to cited text no. 16


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