15.1.3 Antibiotic Resistance (MRSA)
Natural Selection in Action: The Superbug Crisis
🎯 Syllabus Focus: How bacteria evolve resistance through mutation and natural selection (18.3.5)
The Antibiotic Resistance Crisis
🦠 What's Happening?
Some bacteria survive antibiotics even when the drug should kill them. Why?
💥 MUTATION: Random changes in bacterial DNA create new alleles that provide resistance.
🔄 The 4-Step Death Spiral
Variation
Population has genetic variation - some bacteria carry resistance alleles (mutation), most don't.
Selection Pressure
Antibiotic kills ALL non-resistant bacteria. They die before reproducing.
Survival
Only resistant bacteria survive. They reproduce by binary fission.
Allele Frequency Shift
Resistant bacteria pass resistance alleles to offspring. The WHOLE population becomes resistant.
How to Prevent Resistance
Only Use When Essential
Don't use antibiotics for viral infections (colds, flu). Antibiotics kill bacteria, NOT viruses.
Complete the Full Course
Even if you feel better, finish ALL pills. Stopping early leaves the STRONGEST bacteria alive.
🔑 Keyword Bank (Exam Essential)
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