Antibiotic resistance

Evolves when random mutations produce resistant bacteria, and the antibiotic selects these by killing susceptible ones, so the proportion of resistant bacteria increases over generations.

Mutations can produce bacteria that are resistant to penicillin, so it is no longer reliably effective and alternative antibiotics or treatment combinations are needed.

Bacteria that are less affected by the drug may survive and reproduce, so the population becomes dominated by bacteria the antibiotic cannot treat.

Arises when random mutations in bacterial DNA give some bacteria an advantage against an antibiotic, so the resistant strain becomes more common.

Rare random mutations in bacteria produce alleles conferring resistance to specific antibiotics, so resistant strains survive and multiply.

Overuse or incomplete courses can allow resistant bacteria to survive, and the bacteria become resistant, not the person.