CONSEQUENCES TO MICROBIAL DIVERSITY
With the declaration of the coronavirus COVID-19 pandemic in 2020, Australians implemented major restrictions to reduce the respiratory droplet and aerosol contact1 transmission of the novel severe-acute respiratory syndrome Coronavirus 2 (SARS-CoV-2). The pandemic prompted public health messaging advising Australians to minimise physical contact, maintain 1.5 metres distance from others, wear a face mask2 and wash and sanitise hands regularly,3 particularly after contact with others. As a predominantly respiratory infection, COVID-19 binds with alveolar and small intestinal epithelial angiotensin-converting enzyme 2 (ACE2) receptors, drawing attention to the gut and respiratory microbiome.4
The microbiota
The human microbiome is influenced by our hygiene practices, vaccination protocols, antibiotic use, and how we are born.1 An infant’s microbiome is enriched through the contact they have with objects explored with their hands and tongue, allowing them to ingest a diverse range of microorganisms. Modern-day behaviours contribute to changes in our ancestral microbial heritage. Recent increases in the use of antibacterial products and hand washing can interfere with the natural microbial inoculation in children.5 The microbiota is responsible for immune system development4 and regulation of T-regulatory, T helper 1, and T helper 17 cells impacting inflammation and immune responses.6 Increased COVID-19 severity has been demonstrated in the elderly, obese, and those with
chronic conditions, with the microbiota playing a role in the development of chronic, non-communicable diseases.4
The skin microbiota
Beneficial skin and gastrointestinal bacteria are susceptible to destruction from hand sanitisers and alcohol, leading to dysbiosis-producing gastrointestinal symptoms, inflammatory bowel diseases, obesity, and chronic heart disease,7 ironically increasing the risk and severity of COVID-19.
The lung microbiome
The lung microbiome is a dynamic environment with the continuous bidirectional movement of air and mucus into the alveoli, with dysbiosis connected to lung pathologies.1 Exposure to unhygienic environments and air microbes support stronger respiratory immune response development and may be associated with the variation of COVID-19 death rates in different countries.1
The gastrointestinal microbiome
COVID-19 infection induces gut dysbiosis through the reduction in short-chain fatty acid production, with beneficial bacteria inversely associated with viral load, COVID-19 severity, inflammation and upregulation of ACE2 receptors in the gut,11 lungs and oesophagus.4
Microbial samples from the gut of COVID-19 patients demonstrate reduced bacterial diversity, with increases in opportunistic pathogens associated with the severity of COVID-19 and inversely related to the number of beneficial bacteria present.1 COVID-19 is associated with increases in interleukin-6 and interleukin-10, relative to disease severity,2 prompting the recommendation for prophylactic inflammation and immune modulation to reduce and prevent COVID-19 disease.12
Future generations born during the pandemic may have altered microbiomes. A higher caesarean delivery rate during COVID-19 has been found in both infected and uninfected women11,13 which is proven to impact the newborn microbiota.14
Social connection and the microbiota
Social connection allows humans to share microorganisms and maintain commensal bacteria,14 supporting health and the immune response. While social distancing may limit the spread of COVID-19, it also reduces intestinal and oropharyngeal microbial diversity, impacting pulmonary viral infection progression and negatively impacting the prognosis for COVID-19 patients.5
The physiological impact of lockdowns
Low vitamin D levels contribute to the body’s decreased antiviral response in the pulmonary and gastrointestinal epithelial cells, connecting a reduction in vitamin D levels due to reduced skin exposure to sunlight during lockdowns with increased COVID-19 severity.15
Alterations in sleep patterns and circadian rhythm can be the product of dysbiosis reducing serotonin and melatonin production,15 increasing the risk of diabetes, cardiovascular disease, cancer, and metabolic syndrome and, in-turn, increasing the risk of severe COVID-19.16
Stress adversely impacts microbial diversity by increasing proinflammatory cytokine secretion, impairing tight-gap junctions, and increasing gut permeability, and dysbiosis thereby increasing the susceptibility for COVID-19 infection.15
WHERE TO FROM HERE?
It is important to establish and maintain microbial diversity in the face of lockdowns, social distancing, and new hygiene challenges.
We can do this through the use of probiotics4 and the promotion of a diet rich in diverse prebiotic and probiotic foods to support epithelial cell health.8
Dietary soluble and insoluble fibre support the microbial production of short-chain fatty acids for optimal enterocyte and respiratory tract health, a healthy diverse microbiota4 and a reduction in inflammation.12
The consumption of essential fatty acids, zinc, diverse and colourful fruits and vegetables also support the immune response, and the natural antioxidant and anti-inflammatory functions of the body. Vitamin D supplementation may benefit those with reduced synthesis and exposure to the sun,15 while vitamin A supplementation may support the intestinal barrier function and immune responses.6
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