Christine Rosche, MPH,CNS,CBT

Adapted from Research by Leo Galland, MD

Leo Galland MD has been researching the interaction of the gut microbiome with Covid-19 since the start of the pandemic. The science is complex, but it leads to specific recommended actions, which come at the end of this section.

The following is a summary of Dr. Galland research and findings

Your body teems with microbes, tens of trillions of them. Collectively they are called the microbiome. They include bacteria, viruses, fungi, and –for most people in the world—worms and protozoa, like amebas. Bacteria have been the most studied; 99% of them are found in your large intestine. Because two-thirds of your lymphocytes make their home in the small intestine, there has been extensive investigation into the cross-talk between gut bacteria and immune function.

A lot’s been published about the impact of gut bacteria on respiratory health[130] and on viral infections[131], so the early months of the pandemic saw considerable speculation about a link between gut microbes and Covid-19. Actual evidence began to emerge late in 2020. It derives from studies of patients in hospitals and the numbers are small, but it presents a coherent picture.

First, people hospitalized with Covid-19 show profound changes in the bacterial microbiome as measured in stool specimens. Some of these changes may represent the impact of hospitalization, but there is a deeper connection. ACE2 has a special function in the small intestine. It acts as a chaperone for an enzyme that transports amino acids into the body. Damage to intestinal ACE2 creates amino acid deficiencies that impair gut immunity and barrier function[132], producing abnormalities in the microbiome (this state is called dysbiosis) and increased permeability of the intestinal lining (the so-called “leaky gut.”)[133]. Intestinal leakiness in Covid-19 is associated with damage to the heart[134].

Covid-19 decreases diversity and richness of bacteria in the gut microbiome, with depletion of some beneficial species and overgrowth of others considered undesirable.[135] In contrast, Covid-19 increases the richness of yeasts and fungi in the gut (the mycobiome)[136]. The predominant fungal opportunists promoted by Covid-19 are the well-known yeast, Candida albicans, its scary cousin Candida auris (which has received global attention as an invasive drug-resistant species[137]), and the potent allergen, Aspergillus flavus. These organisms persist in stool even after respiratory symptoms have cleared and nose or throat swabs show no active viral infection.

To date, no one has studied the impact of fungi in Covid longhaulers, but I’ve been investigating, treating and teaching about yeast and fungal overgrowth for over 40 years and I’ve seen what they can do. Intestinal fungi can exert potent, often undesirable, effects on immunity, inflammation and metabolism that create symptoms in many body systems. Stool testing for bacteria and yeast should be considered in all people with persisting post-Covid symptoms.

Some researchers have attempted to correlate specific bacterial disturbances with severity of Covid-19. Two provocative findings have appeared. First, severity correlates with lower levels of a key anti-inflammatory species called Faecalibacterium prausnitzii. Loss of Faecalibacterium prausnitzii and its friends, the Bifidobacteria, persists for weeks after hospitalization, and correlates with increased severity of systemic inflammation.

A study from the University of Massachusetts found that excessive growth of one species, Enterococcus faecalis, in fecal or oral specimens, was the best predictor of severe disease, more accurate than symptoms or underlying medical conditions.The study’s authors note that Enterococcus faecalis is a potent stimulator of inflammation. They believe it actively contributes to worse outcomes for people with Covid-19. Theirs is a reasonable theory, because the use of Enterococcus faecalis as a probiotic provokes the release of gamma-interferon, a major driver of the cytokine storm of severe Covid (mentioned above in IMMUNITY).

Possible support for the importance of the oral microbiome in Covid-19 comes from a study done in Bangladesh[142]. In a randomized controlled clinical trial, medical researchers told patients newly diagnosed with Covid 19, to use a povidone/iodine mouthwash (plus a nasal wash and eye drops) or use only warm water to flush their mouth, nose and eyes. The solutions were used every 4 hours for 4 weeks. Povidone iodine reduced the need for hospitalization and oxygen therapy by 84% and the death rate by 86%, compared to warm water. The researchers attributed the benefits to killing of the SARS-CoV-2 virus in the nose, mouth and throat, but by the time they were treated, these patients were already sick with Covid-19, making it likely that the infection was already systemic. Povidone/iodine kills bacteria as well as viruses and is quite effective at killing Enterococcus faecalis and other oral pathogensso it is possible that eliminating pro-inflammatory bacteria from the mouth improved the outcome of disease in their patients.

So, here’s the good news: 

If an unbalanced microbiome creates sickness in people with Covid-19, restoring balance should lead to milder disease. Overgrowth of Enterococcus faecalis can be reversed. In addition to the use of an iodine-based gargle (which may only be needed once symptoms occur), there are several natural substances and dietary factors that can correct the specific microbiome imbalances described in Covid-19.

Resveratrol, a polyphenol that enhances activity of ACE2, inhibits the growth of Enterococcus faecalis[143] [144]  and curcumin, another natural ACE2 enhancer, decreases bacterial virulence by breaking up biofilms that support the growth of Enterococcus faecalis[145] [146]

Ursolic acid is a dietary compound found in many fruits, vegetables, herbs and spices and is used as a muscle-building supplement by body builders. Ursolic acid has anti-inflammatory, anti-viral and cancer-fighting activity[147]. It also inhibits the growth of Enterococcus faecalis[148]. Dietary sources of ursolic acid include apple peel, cranberries, bilberries, blueberries, prunes, peppermint, rosemary, oregano, thyme, sage, and marjoram. Dried cranberries are an especially good source[149].. Human clinical trials of ursolic acid show anti-inflammatory effects at doses of 150 mg taken 1 to 3 times a day[150] [151]. Ursolic acid may also inhibit the SARS-CoV-2 Main Protease[152] [153] (The importance of this enzyme is described above  in AFTER ENTRY: THE ROLE OF NSPs).

Just as nutritional strategies can control colonization with the inflammatory organism Enterococcus faecalis, they can support growth of the anti-inflammatory Faecalibacterium prausnitzii, which is fed by fiber-rich foods[154], fiber supplements[155] [156], and certain prebiotics[157]. Daily consumption of chick peas[158] or of avocados[159] increases abundance of F prausnitzii in human volunteers.

Although probiotics based on F. prausnitzii do not exist, two commercial probiotics can increase its levels, according to human clinical trials. Bifidobacterium longum BB536 increases the growth of F. prausnitzii at the same time it relieves symptoms of pollen allergy in adults[160] or upper respiratory infection in young children[161]. Bacillus coagulans GBI-30, 6086 [GanedenBC(30)] was shown to increase growth of F. prausnitzii in men and women over the age of 65[162]. Bacillus coagulans pre-treatment also enhanced the effect of prebiotics in stimulating growth of F. prausnitzii in a clinical trial of older adults.[163]


A customized protocol for building a Covid fighting microbiome, based on testing the stool and implementing customized probiotics, digestive enzymes and other supplements is highly recommended as a key factor in prevention and treatment of Covid-19

Christine Rosche, MPH,CNS,CBT

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