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Petri Dish

From Accident to Antibiotic

Have you ever wondered what a world without penicillin might look like? What if we were deprived of
one of the most potent antibiotics ever discovered? Where would we be now without Alexander Fleming's
Eureka moment...


In science, discoveries often emerge from extensive research, but sometimes they are born from the
fusion of serendipity and scientific curiosity. On September 3, 1929, Scottish bacteriologist Alexander
Fleming stumbled upon one such discovery that would alter the course of medicine.


This article delves into the story of Alexander Fleming's 'Eureka Moment' in the discovery of penicillin,
the world's first wonder drug.


1920s Medical Landscape
To grasp the significance of Fleming's discovery, it's important to comprehend the medical landscape of
the 1920s. Bacterial infections, even minor ones, were life-threatening as there were a limited number of
treatments. Out of 100,000 people, 202 deaths were caused by bacterial infections.


The Eureka
Alexander Fleming, a professor at St. Mary's Hospital in London, was conducting research on
staphylococci bacteria, exploring their infectious properties. During a brief vacation, he unintentionally
left a petri dish containing the bacterial culture outside the incubator. This allowed mold spores to drift
onto the dish.
Upon his return two weeks later, he found the petri dish contaminated. Bacterial colonies had grown in
some areas, but the areas with mold growth displayed an absence of bacteria. He later discovered that the
mold was 'Penicillium notatum,' and the substance it produced was 'Penicillin.'
This discovery epitomizes a true 'Eureka Moment.'


How Penicillin Kills Bacteria
Peptidoglycan molecules form strong links that give the cell strength and prevent
leakage from the cytoplasm. Penicillin disrupts the synthesis of peptidoglycan,
which is in a constant state of breakdown and rebuilding. It intervenes by binding
to DD-transpeptidase, the transpeptidation that crosslinks the peptide side chains
of peptidoglycan strands, preventing its reconstruction and the bacterium from
closing holes in its cell wall.


The water concentration in the surrounding fluid is higher than inside the cell, which allows
water to rush in, causing the bacterium to burst. Remarkably, penicillin can kill harmful
bacteria while sparing human cells, as human cells don't contain peptidoglycan.


Within bacteria, there are two types of cell wall.


Gram-positive: peptidoglycan layer on the outside of the cell wall.
Gram-negative: peptidoglycan between membranes.

Figure 1: A simple diagram of how Penicillin works

Figure 2: Diagram of Gram positive
and negative bacterium structure

Penicillin works best on gram-positive bacteria, making the cells leaky and fragile. The immune system
can therefore breakdown the bacteria more easily, helping the sick person heal more quickly.

Value to the Modern World

Why does a discovery made a century ago still hold relevance in our modern world? The answer is multi-
faceted.

1. Fleming's discovery sparked a revolution in medicine. The most commonly known infections,
such as tonsillitis, are life-threatening if left untreated; however, penicillin reduces this fatality
rate. In WW2, penicillin was able to save many lives—death rates from bacterial pneumonia
decreased from 18% to 1%, saving the lives of 1/7 of the UK's soldiers
2. Antibiotic Resistance: While antibiotics have saved countless lives, their overuse has spawned
antibiotic-resistant bacteria—a global health concern. Some bacteria have developed resistance to
penicillin, highlighting the importance of responsible antibiotic use, which is inspired by
Fleming's discovery.

3. The Role of AI:
Fleming inspired the search for new antibiotics.
With the growing use of AI, the search for new antibiotics become
more efficient. The number of chemicals that need to be tested in a lab
decreases as machine learning algorithms can analyze large datasets of
chemical compounds and determine which are likely to have antibiotic
activity. This process, known as in-silico screening, has the potential to
quicken antibiotic discovery.
By analyzing the structures of existing antibiotics and their interactions with bacteria, AI can develop new
compounds programmed for antibiotic activity. This method could create new antibiotics that are less
likely to cause adverse side effects while being more effective against antibiotic-resistant bacteria.
MIT researchers have achieved a significant breakthrough by using machine learning algorithms to
identify a medicine named Halicin which killed several strains of bacteria. Partnering with researchers
from McMaster University, they also discovered a potential antibiotic to fight the bacteria ‘Acinetobacter
baumannii', commonly found in healthcare facilities, where it can persist on surfaces for long periods and
result in pneumonia, meningitis, and wound infections.
Alexander Fleming's 'Eureka Moment' in discovering penicillin transformed medicine and saved over 200
million lives. His accidental observation of a mold's antibacterial properties set in motion a revolution that
continues to shape healthcare today.
“I did not invent penicillin. Nature did that. I only discovered it by accident.” Alexander Fleming

By: Parita (Pam) Phanratanamongkol

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