Antibiotic resistance evolves in bacteria when ________.

• A. bacteria are exposed to antibiotics and mutations that confer resistance are selected for
• B. bacteria are not exposed to any antimicrobial agents
• C. antibiotic use is strictly limited to laboratory experiments
• D. antibiotics are used only to treat viral infections

Answer: (A)

Verified step by step guidance

1. Understand that antibiotic resistance in bacteria arises through natural selection, where genetic mutations that provide survival advantages in the presence of antibiotics become more common.
2. Recognize that exposure to antibiotics creates selective pressure, meaning bacteria with mutations that confer resistance survive and reproduce, while susceptible bacteria are killed off.
3. Note that if bacteria are not exposed to antibiotics, there is no selective pressure favoring resistant mutants, so resistance does not evolve or spread significantly.
4. Realize that misuse of antibiotics, such as using them to treat viral infections (where they are ineffective), can contribute to unnecessary exposure and promote resistance.
5. Conclude that the key factor driving antibiotic resistance evolution is the exposure of bacteria to antibiotics combined with the selection of resistant mutants.