Topic overview

Start with the big picture

Intrinsic resistance is a baseline property linked to a bacterium’s structure or physiology, such as lacking a drug target or limiting drug entry. Acquired resistance can arise when spontaneous chromosomal mutations produce rare resistant cells before treatment; antibiotic exposure then favors their survival and expansion. Resistance genes also move between bacteria by conjugation, transformation, and transduction, sometimes on mobile DNA elements carrying multiple determinants. The wider picture includes natural environmental reservoirs, antibiotic use in people and animals, healthcare settings, biofilms, and the movement of resistant organisms through travel and trade. Together, these mechanisms and selection pressures explain why resistance is not caused by a single process and why its origins matter to clinical care and public health.