Antibiotics are often hailed as miracle drugs, capable of curing once-deadly infections and saving countless lives. However, the overuse and misuse of antibiotics in humans, animals, and agriculture have severe and often overlooked consequences. While the world is acutely aware that such practices drive antimicrobial resistance (AMR), a more insidious danger lies beneath the surface. The true peril is the profound disruption antibiotics cause to the microbiome — a disruption that ripples out to affect every organ and function of our bodies.

The human body is home to a vast, intricate community of microorganisms collectively known as the microbiome. This includes bacteria, fungi and viruses. Astonishingly, our bodies host approximately 38 trillion microbial cells, outnumbering our own cells, which total around 30 trillion. This means we are more microbial than human. The gut microbiome, in particular, plays a crucial role in maintaining our health. It aids in digestion, supports the immune system, produces essential nutrients like vitamin K and certain B vitamins, and protects against pathogens. The diversity and balance of these microbial communities are vital for our well-being.

While antibiotics are essential for treating bacterial infections, their irrational use can wreak havoc on the microbiome. Antibiotics do not discriminate between harmful pathogens and beneficial bacteria. When we take antibiotics, especially the broad-spectrum ones, they wipe out a large portion of the gut bacteria. This disruption, known as dysbiosis, can have severe and long-lasting effects. Even a single course of antibiotics can produce dysbiosis that lasts for months or even years.

Dysbiosis can cause more severe conditions like inflammatory bowel disease and irritable bowel syndrome. A healthy microbiome is essential for a robust immune system. Dysbiosis can impair immune function, making the body more susceptible to infections and autoimmune diseases. The gut microbiome also plays a crucial role in regulating metabolism.

The gut microbiome interacts with various organs through complex networks known as gut-organ axes. These interactions influence the overall health and functioning of the body. The gut-brain axis links the gut microbiome with the brain, where dysbiosis can alter neurotransmitter levels and brain chemistry, affecting mood, cognition, and mental health conditions like anxiety and depression. The gut-liver axis involves the transport of bacterial metabolites and toxins from the gut to the liver. Dysbiosis can increase gut permeability (‘leaky gut’), allowing more toxins to reach the liver and exacerbating liver conditions such as non-alcoholic fatty liver disease. The gut-skin axis involves the influence of the gut microbiome on skin health, where dysbiosis can exacerbate conditions like acne, eczema, and psoriasis by altering systemic immune responses and skin barrier function. The gut microbiome influences metabolic processes, including energy harvesting from food and the regulation of glucose and lipid metabolism. Dysbiosis can disrupt these processes, contributing to conditions like obesity, diabetes, and metabolic syndrome.

Beyond the gut, the microbiome also plays crucial roles in other parts of the body. The skin microbiome protects against harmful microorganisms and supports skin health. The respiratory tract microbiome helps defend against respiratory infections and maintains respiratory health. Antibiotic use can potentially lead to respiratory conditions such as asthma and chronic obstructive pulmonary disease. The genitourinary microbiome, which includes the vaginal and urinary microbiomes, protects against infections and maintains urinary and reproductive health. Dysbiosis in these areas can result in conditions like bacterial vaginosis and urinary tract infections.

One particularly concerning aspect of antibiotic use is its impact on colonisation resistance. This is the ability of the native gut microbiome to protect against colonisation by pathogenic microorganisms. Beneficial bacteria consume available nutrients, limiting resources for pathogens. By occupying adhesion sites on the gut epithelium, commensal bacteria prevent pathogens from attaching and establishing themselves. Antibiotic use can reduce colonisation resistance, allowing harmful bacteria to take hold and proliferate, increasing the risk of infections.

Given the profound impact of antibiotics on the microbiome and the long-term health consequences of dysbiosis, it is crucial to use antibiotics judiciously. Implementing alternative practices, such as better hygiene, vaccination, and the use of bacteriophages, can reduce the reliance on antibiotics.

Antibiotics have revolutionised medicine, but their misuse poses serious threats. The concept of medicine being a poison when misused is particularly relevant here. In the right hands, these miracle molecules cure infections and save lives. However, if misused, they disrupt the microbiome and contribute to a host of health problems, essentially becoming poisons. Antibiotics are a prime example of the medicine-poison paradox. Preserving the balance of our microbiome is essential for maintaining our health. We must carefully consider our use of antibiotics before taking them.

(Abdul Ghafur, Consultant in Infectious Diseases, Apollo Hospital, Chennai and Coordinator of Chennai Declaration on AMR)