What is the human microbiome?
The human microbiome is comprised of the vast populations of bacteria that reside along the skin, in the gut and other organs. How many are there? Well, it is estimated that cells comprise about only 20% of the cells in the human body and bacteria and other unicellular organisms make up the rest. Most of these organisms reside in the gut and play an important role in the production of proteins, enzymes and other substances necessary for metabolism and for protecting against invading pathogens.
Any imbalance within this ecosystem can lead to diseases and other health problems. The primary drivers of gut microbe imbalances are excessive use of antibiotics and consumption of highly processed foods that have high levels of sugar and fat. While it was Hippocrates who, over two thousand years ago, said “All disease begins in the gut,” we are now just beginning to realize the importance of intestinal bacteria.
What is the effect of microbiome imbalance in COPD?
Traditionally, it was thought that such infections in the lungs originated from large populations of bacteria in the mouth and nose. For example, the most common form of pneumonia, known as aspiration pneumonia, is caused by aspirating fluids often contaminated with bacteria. In fact, most cases of pneumonia don’t originate from person-to-person contact, but rather though aspiration of oral secretions, loose and rotted teeth, sinus infections and other regions where there’s bacterial overgrowth.
New research, however, shows that there is a normal population of bacteria in the lungs, similar to gut microbiome. An example are studies of patients with cystic fibrosis, which have revealed various populations of cells and bacteria in the lung.
More importantly, we now know that it’s the loss of normal bacterial diversity that leads to overgrowth of one species of bacteria, causing a pathological imbalance, much like how antibiotics can disrupt the delicate balance of microbes in a person’s gut. So it’s not changes in the quantity of bacteria during lung infections, but rather the shift of different populations that disrupts the normal balance and can lead to illness and inflammation.
How does this relate back to COPD? A major cause of COPD is cigarettes, which impairs the clearance of secretions by the cilia in the lung’s airways and instigates cycles of inflammation within the lungs. That is why antibiotics are given repeatedly for COPD exacerbations.
We also know now that bacteria like lactobacillus may regulate the inflammatory response caused by the overgrowth of pathogenic bacteria and actually protect the lung from inflammation and oxidative stress. This is important because unlike the gut, the lung airways are exposed to oxygen in the air and need different type of protection against the oxygen radical molecules that cause oxidative stress.
So would an imbalance of gut microbes affect lung health?
This does not mean that the lungs are entirely unaffected by changes in the gut microbiome. One study, for example, shows that antibiotic treatment can alter the balance of gut bacteria balance and impair the production of flu antibodies, which decreases the lymphocyte response involved in fighting off viruses. Because many patients will typically request antibiotics despite the fact that many respiratory infections are viral in nature, studies such as this show how they’re not only ineffective, but can also disrupt the normal immune response.
By the same token, recent studies have shown that smoking and COPD have an effect on the gut microbiome. This may explain the relationship between smoking and risk of inflammatory diseases of the bowel like ulcerative colitis (UC).
Does early microbiome development have consequences for long-term health?
In an earlier sharepost, I suggested that exposure to certain bacterial infections during childhood can help build protection against developing asthma in adulthood. This happens through the Hygiene Hypothesis, in which these initial exposures prime lymphocytes to produce defensive agents called interleukins.
There’s also a theory that suggests babies born through the vaginal canal are able to develop healthy bacterial colonies of lactobacillus because they are bathed in the mother’s vaginal secretions. Babies born by C-section don’t pass through the canal and harbor bacterial colonies similar to skin bacteria such as staphylococcus and acinetobacter, which may increase their risk of developing asthma.
Does that mean that taking antibiotics is always wrong?
Use of antibiotics should be carefully weighed and considered. Any confirmed bacterial illness usually requires antibiotic therapy. Antibiotics, however, shouldn’t be used with viral infections. And in cases where antibiotics are administered, it’s now recommended to augment treatment with a course of probiotics and continue taking them until your gut microbiome balance is restored.
The other new finding is that some antibiotics do more than just kill bacteria. The best example is Azithromycin (Zithromax), which is sometimes prescribed for months at a time in cystic fibrosis and HIV patients. It’s been shown to also have an anti-inflammatory effect that is crucial to the treatment of these diseases.
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Eli Hendel, M.D. is a board-certified Internist and pulmonary specialist with board certification in Sleep Medicine. He is an Assistant Clinical Professor of Medicine at Keck-University of Southern California School of Medicine, Qualified Medical Examiner for the State of California Department of Industrial Relations, and Director of Intensive Care Services at Glendale Memorial Hospital.His areas of expertise in private practice include asthma, COPD, sleep disorders, obstructive sleep apnea, and occupational lung diseases.