How bacteria evolve and survive antibiotics

Humanity has been warned. First, by Sir Alexander Fleming, and now, decades later, by the World Health Organization: if Antimicrobial Resistance (AMR) isn’t addressed, it could cause millions of preventable deaths each year.

It’s a scary thought. But do people truly understand the threat?

While researchers understood AMR through lab studies and clinical data, communicating its urgency to the public needed something more powerful. So scientists at Harvard Medical School and Technion-Israel Institute of Technology devised a powerful way to display bacterial evolution in response to antibiotics in a strikingly visual way.

Evolution on display

Famously known as the MEGA-Plate Petri dish experiment, or Microbial Evolution and Growth Arena plate, this study showed how bacteria evolve resistance over time. To capture bacterial mutations as they occurred, researchers designed a large petri dish filled with a nutrient-rich agar medium. At 2-feet long and 4-feet wide, the dish was divided into zones with increasing antibiotic concentrations, from none on the outer edges to extremely high levels at the centre.

E. coli bacteria were introduced to the outer edges, and as they multiplied, they began to spread toward the next zone with a low dose of antibiotics. In each antibiotic zone, some bacteria mutated to develop resistance, allowing them to survive and move inward. As the bacteria approached the highest concentration zones, only the most resistant strains continued to thrive.

The experiment illustrated natural selection in action, as viewers watched bacteria evolve from lower to higher antibiotic zones over two weeks. Time-lapse images captured the bacterial waves as they mutated and advanced inward. 

When bacteria fight back

The MEGA-plate experiment demonstrated how bacterial resistance develops gradually, underscoring the dangers of using low or sub-lethal doses of antibiotics, reinforcing the critical need for appropriate antibiotic use to prevent the rise of superbugs.

As bacteria progressed across the petri dish, even small populations adapted to survive, showing just how difficult it is to contain resistance, highlighting the urgency of developing alternative treatments and improving antibiotic stewardship to avoid a future where even routine infections become untreatable.

World as a petri dish

The MEGA-plate experiment is a powerful analogy for how our world acts as a breeding ground for microbial evolution, and, by extension, antibiotic resistance. Just as bacteria evolved within the controlled petri dish, microbes mutate and adapt in various ecosystems, such as soil, water, and even within our bodies, often at an accelerated pace due to human activity.

Let’s look up close.

Soil, one of the richest microbial habitats, is home to a vast diversity of bacteria and fungi, many of which naturally produce antibiotics. These microbes develop resistance genes as a survival mechanism, spreading them to other bacteria through horizontal gene transfer. Agriculture further accelerates this process by introducing antibiotics in livestock farming, creating an environment where resistant strains thrive.

Waterways face a similar threat. Antibiotic residues and resistant bacteria from sewage, agricultural runoff, and industrial waste enter rivers, lakes and oceans. The water bodies act as conduits, enabling bacteria to transfer genes across diverse species, driving global antibiotic resistance.

Our bodies are not exempt; our gut microbiomes host trillions of microbes, some of which can mutate or acquire resistance genes when exposed to antibiotics. This makes our microbiomes potential incubators for antibiotic resistance, especially with improper or excessive antibiotic use.

All of these encourage the survival of only the most resistant strains, creating superbugs that withstand multiple drugs. Our actions–through antibiotic overuse, improper waste disposal, and agricultural practices–are speeding up microbial evolution and resistance.

Wake-up call

The MEGA-plate experiment is a stark wake-up call, vividly illustrating that AMR is not just a scientific concern but a global threat. The rapid spread of AMR highlights how our world has become a vast breeding ground for resistant microbes. With certain infections already becoming untreatable, AMR poses a serious threat to global health, endangering surgeries, cancer treatments, and routine medical care. The thought of a post-antibiotic era–a future where minor injuries or common infections could be fatal–is daunting.

Combating this looming crisis requires a unified response, advancing antibiotic stewardship, investing in new treatments, and adopting practices that limit the spread of resistant bacteria across healthcare, agriculture, and communities. Acting now is the only way to ensure the future of modern medicine and protect generations to come.

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