What Is a Mutation?
A mutation is a random change in the DNA of a cell.
In bacteria, mutations happen naturally and frequently because they reproduce very fast—sometimes in minutes.
These changes can be harmful, neutral, or help the bacteria survive — that’s when resistance begins.
Step-by-Step: How Resistance Happens
Step 1: Antibiotic Is Taken
You take an antibiotic to kill bad bacteria. Most bacteria die, but a few naturally resistant ones may survive because of a mutation in their genes.
Step 2: Resistant Bacteria Survive and Multiply
The antibiotic kills off the weak bacteria. The mutated bacteria survive, and since there’s no competition left, they start reproducing rapidly.
Step 3: Resistance Gene Spreads
These resistant bacteria can pass on the resistance gene to their offspring. Even more dangerously, they can share their genes with other bacteria, even of different species. This is called Horizontal Gene Transfer (HGT).
Horizontal Gene Transfer (HGT)
Bacteria can:
Send resistance genes through plasmids (small DNA circles)
One resistant bug can 'teach' others how to fight antibiotics
Mutation Examples
Here are common types of bacterial mutations or tricks that lead to resistance:
Altered target – Changes the part of the bacteria where antibiotic binds, so drug can't work.
Efflux pumps – Bacteria develop a 'pump' to throw the antibiotic out.
Enzyme production – Bacteria produce enzymes (like beta-lactamase) that destroy the antibiotic.
Biofilm formation – Bacteria build a sticky shield that protects them from antibiotics.
Example: MRSA
MRSA (Methicillin-Resistant Staphylococcus aureus) developed a mutation in a gene called mecA.
Normal penicillin-like antibiotics target a bacterial protein needed for making its cell wall.
MRSA mutated that protein, so antibiotics can’t bind and kill it anymore.
Why Is This a Global Problem?
Because bacteria: Multiply super fast
Mutate randomly but often
Share resistance with others
And humans are overusing antibiotics, giving bacteria more chances to 'train' and evolve.
Summary
Bacteria mutate by:
Random genetic changes
Natural selection (only the resistant survive)
Sharing genes (horizontal transfer)
These superbugs:
Can’t be killed by normal antibiotics
Cause severe infections
Are very hard to control
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