Our bodies contain as many, if not more, bacterial cells as human cells. Along with fungi and viruses, these microbes collectively form our microbiome. Microbes, particularly in our gut, have a profound impact on health. Major discoveries have unearthed that what we eat and the drugs we take shape the composition of our microbiome, which in turn affects the effectiveness of treatments for diseases. Everything is interconnected, creating a full circle of interaction.
Antibiotics are crucial for treating bacterial infections,
Our bodies contain as many, if not more, bacterial cells as human cells. Along with fungi and viruses, these microbes collectively form our microbiome. Microbes, particularly in our gut, have a profound impact on health. Major discoveries have unearthed that what we eat and the drugs we take shape the composition of our microbiome, which in turn affects the effectiveness of treatments for diseases. Everything is interconnected, creating a full circle of interaction.
Antibiotics are crucial for treating bacterial infections, but since they do not discriminate between harmful and harmless bacteria, they can also disrupt the balance of our microbiome. When beneficial bacteria are wiped out, harmful ones can proliferate, increasing the risk of other health concerns.
While antibiotics are designed to kill bacteria, we are now finding out that other drugs have unintended effects on our microbiome. In a groundbreaking study published in Science in March, Amir Mitchell and colleagues at the University of Massachusetts Medical School discovered that even non-antibiotic drugs can have unintended consequences. For instance, the study found that the antidepressant sertraline and the cancer drug streptozotocin can slow down bacterial growth in ways distinct from antibiotics. On the positive side, these drugs could be repurposed to create new antibiotics. However, some non-antibiotics can inadvertently promote antibiotic resistance, complicating efforts to manage drug-resistant infections.
In India, a class of drugs known as proton-pump inhibitors (such as omeprazole and pantoprazole) are frequently taken to treat acid reflux. These drugs work by reducing stomach acidity. When the stomach's natural acidity is lowered, it can promote the growth of certain bacteria while inhibiting others. This imbalance can lead to an increased risk of infections.
Many other drugs have been found to have side effects on health that are mediated through changes in the gut microbiome. For example, antipsychotic use has been linked to weight gain and metabolic syndrome, likely caused by changes in gut bacteria. On the other hand, metformin, a common drug for type 2 diabetes, increases several beneficial bacteria.
It's not just drugs that influence our health through the microbiome. Microbes also affect how well drugs work.
Recent research has shown that gut bacteria affect the efficacy of cancer treatments, particularly drugs known as immune checkpoint inhibitors, which help the immune system recognise and attack cancer cells. Immune checkpoint inhibitors are more effective in patients with a favourable balance of gut microbes.
Laurence Zitvogel and her team at the Gustave Roussy Cancer Campus in France studied the gut microbiome of 245 lung cancer patients. Publishing their work in Cell last month, they identified two distinct groups of bacteria. One group was linked with resistance to immune checkpoint inhibitors, while the other was linked to positive treatment responses.
By analysing the ratio of these bacterial communities, the researchers created a score that could predict how well a patient would respond to cancer treatment. This score was then tested and confirmed in other cancer patients. The researchers developed a simple test that looks for 21 key gut bacteria types. This test can quickly and accurately assess the balance of beneficial and harmful bacteria, providing doctors with a powerful tool to guide treatment decisions.
The beauty of this study is that it doesn’t stop at how well drugs might work to treat diseases. In the future, once we identify certain bacteria that enhance the positive effects of drugs, we can try to increase their presence in the gut microbiome. Tumours disrupt the gut microbiome, increasing harmful bacteria, and making treatments less effective. However, introducing healthy bacteria might restore balance and improve the effectiveness of cancer drugs. It’s a virtuous cycle.
What’s abundantly clear from both studies is that the human microbiome is a major component of health. From the impact of antibiotics and non-antibiotics to the role of the microbiome in cancer therapy, our microbial communities are intricately linked to our well-being. As research in this exciting field progresses, we will likely uncover even more ways our invisible microbial residents shape our health.
Anirban Mahapatra is a scientist and author, most recently of the popular science book, When The Drugs Don’t Work: The Hidden Pandemic That Could End Medicine. The views expressed are personal.
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