The human microbiota refers to the microorganisms (like bacteria, fungi, and archaea) living in our gut, skin, and respiratory tracts, among other parts of our body. Even though many people are focused on the role of microorganisms in disease, these organisms can also be important for health. The microbiome can influence our immune response, contribute to our metabolism, and serve as protection against some pathogens [1].
Over the course of evolution, our bodies have developed a close relationship with these microorganisms, which can be mutualistic, parasitic, or commensal. A mutualistic relationship is one where both sides benefit (e.g., a “win-win” situation for both the human and the microorganism). A parasitic relationship is where one organism benefits but the other one is hurt. Finally, a commensal relationship is where one side benefits and the other one is not affected (neither positively nor negatively) [2]. It should be noted that the classification of parasitic/mutualistic/commensal depends on many factors. Indeed, a certain microorganism can be mutualistic or parasitic depending on factors like the location, and the condition of the human body, among others [3].
Analyzing the microbiome is also important to understand infection processes. Imagine some of the microorganisms as home residents within the body. When a new pathogen comes into our bodies, they come across the “resident” organisms. Some of these residents do not want to give away space and resources to the “newcomers”. Therefore, sometimes, commensal microorganisms can help promote protection against pathogens. For example, they can modulate the immune system, generate molecules with antimicrobial properties, or compete for resources against the pathogen [3]. On the other hand, there are occasions where our own microorganisms can contribute to the development of the infection and lead to other conditions [3].
In the context of COVID-19, a recent review shows that COVID-19 patients may experience altered microbiomes [4]. For example, based on a small pilot study on the fecal microbiome [5], the number of opportunistic pathogens increased in COVID-19 patients (the term “opportunistic” refers to microorganisms that are usually not harmful for people with healthy immune systems but become pathogenic when the circumstances change and the host becomes more vulnerable [6]). Furthermore, there was a relationship between the severity of COVID-19 and the abundance of certain types of bacteria. Actually, COVID-19 severity could be related to a high abundance of some bacteria like Clostridium ramosum. However, a high level of certain anti-inflammatory bacteria, like Faecalibacterium prausnitzii, and a high amount of Bacteroides, were related to lower COVID-19 severity and lower levels of SARS-CoV-2 in the stool, respectively [5].
The microbiome of the airways is also relevant. In COVID-19 patients, some studies found changes in the airway microbiome [7] and the lower respiratory tract [8]. Although some studies did not find clear differences in the microbiome of the nasopharynx [9], others found that the levels of some bacteria genera can be related to better clinical prospects [10]. On the other hand, patients that passed away from COVID-19 tended to have a decreased microbiome diversity in the nasopharynx [10].
Overall, we need more studies to clearly understand the role of the microbiota in COVID-19. Future analyses should study if the changes in the microbiota are a result of the impaired immune response, which has been compromised by the virus. Moreover, they can assess if interventions could be helpful to regulate the microbiota. This could be particularly important for patients that are immunocompromised or have older ages [11]. For example, a clinical trial is examining the oral microbiome immunity formula in patients that already recovered from COVID-19 [12] (more information here). With more research, we can continue to understand the complex interplay between our microbiome and pathogens such as SARS-CoV-2.
——————————–
Written by : Nicole
Edited by : María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information. For more information about vaccines and their safety profile, please see previous posts or consult with your personal physician. If you have any questions about this topic, please comment or send them to our email.
References:
Shreiner, A. B., et al. (2015). The gut microbiome in health and in disease. Current opinion in gastroenterology, 31(1), 69–75. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4290017/
Dimijian G. G. (2000). Evolving together: the biology of symbiosis, part 1. Proceedings (Baylor University. Medical Center), 13(3), 217–226. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1317043/
Belkaid, Y., & Hand, T. W. (2014). Role of the microbiota in immunity and inflammation. Cell, 157(1), 121–141. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4056765/
Yamamoto, S., et al. (2021). The human microbiome and COVID-19: A systematic review. PloS one, 16(6), e0253293. Available at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0253293
Zuo, T., et al. (2020). Alterations in Gut Microbiota of Patients With COVID-19 During Time of Hospitalization. Gastroenterology, 159(3), 944–955.e8. Available at: https://pubmed.ncbi.nlm.nih.gov/32442562/
Riccardi, N., Rotulo, G. A., & Castagnola, E. (2019). Definition of Opportunistic Infections in Immunocompromised Children on the Basis of Etiologies and Clinical Features: A Summary for Practical Purposes. Current pediatric reviews, 15(4), 197–206. Available at: https://pubmed.ncbi.nlm.nih.gov/31242834/
Zhang, H., et al. (2021). Metatranscriptomic Characterization of Coronavirus Disease 2019 Identified a Host Transcriptional Classifier Associated With Immune Signaling. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 73(3), 376–385. Available at: https://pesquisa.bvsalud.org/global-literature-on-novel-coronavirus-2019-ncov/resource/pt/covidwho-401774
Shen, Z., et al. (2020). Genomic Diversity of Severe Acute Respiratory Syndrome-Coronavirus 2 in Patients With Coronavirus Disease 2019. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 71(15), 713–720. Available at: https://pubmed.ncbi.nlm.nih.gov/32129843/
De Maio, F., et al. (2020). Nasopharyngeal Microbiota Profiling of SARS-CoV-2 Infected Patients. Biological procedures online, 22, 18. Available at: https://biologicalproceduresonline.biomedcentral.com/articles/10.1186/s12575-020-00131-7
Ventero, M. P., et al. (2022). Nasopharyngeal Microbiota as an early severity biomarker in COVID-19 hospitalized patients. The Journal of infection, 84(3), 329–336. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8709923/
Dhar, D., & Mohanty, A. (2020). Gut microbiota and Covid-19- possible link and implications. Virus research, 285, 198018. Available at: https://pubmed.ncbi.nlm.nih.gov/32430279/
Clinical Trials: A Randomised-controlled Trial of an Oral Microbiome Immunity Formula in Recovered COVID-19 Patients. Available at: https://clinicaltrials.gov/ct2/show/NCT04950803
Comments