10.2.3—Antibiotic resistance

Antibiotic resistance is a population change: a chance mutation can produce a resistance allele, and antibiotic treatment selects bacteria that survive, allowing resistance to become more common.

• Variation first: random mutation creates genetic variation; the antibiotic does not direct a bacterium to mutate.
• Selection: treatment kills susceptible bacteria, while a bacterium with a resistance allele survives with less competition.
• Frequency increases: the resistant survivor reproduces, so its allele is passed to more offspring and becomes more frequent in the population. Short generation times, clonal offspring and horizontal gene transfer can speed spread.
• Clinical consequence: commonly used antibiotics can become less effective; multidrug-resistant strains can make infections difficult to treat and require complicated, expensive treatments that may not be available to everyone.

• Reduce selection: prescribe antibiotics only when needed, do not use them for viral infections, avoid unnecessary wide-spectrum use, complete the prescribed course and tighten control of antibiotic use in agriculture.
• Limit spread: maintain good hygiene, especially handwashing or sanitiser use in clinical settings, and isolate infected patients when resistant strains could spread.
• Maintain options: develop new antibiotics and alternatives, recognising that this is expensive and time-consuming.

Antibiotics select pre-existing resistant variants; they do not train every bacterium or create a targeted mutation. Resistance is a change in allele frequency in a bacterial population, not immunity of the patient. The penicillin wall mechanism and the virus target boundary are covered by the neighbouring cards.