Bacterial Antibiotic Resistance Originates from Genetic Changes

Steps:

• Bacteria encounter antibiotics, which kill susceptible populations.
• Random genetic mutations occur in some bacterial DNA, altering proteins targeted by the antibiotic.
• These mutations allow mutated bacteria to survive antibiotic exposure.
• Surviving bacteria replicate, passing on the resistance trait.

Why A is correct:

• Genetic mutation is the initial mechanism per evolutionary biology, as it introduces heritable variations in bacterial genomes that confer resistance.

Why the others are wrong:

• B: Overuse promotes selection of resistant strains but does not create the initial resistance.
• C: Natural selection acts on existing mutations to favor resistant bacteria, not as the starting mechanism.
• D: Incomplete courses increase selection pressure for resistance but do not generate the genetic change.

Final answer: A