1 (in microbiology) The degree to which pathogenic microorganisms remain unaffected by antibiotics and other drugs. Genes for antibiotic resistance are often carried on plasmids or transposons, which can spread across species barriers.
2 (in ecology)
a The degree to which a pest can withstand the effects of a pesticide. It depends on the selection and spread within a pest population of genes that confer the ability to destroy, or minimize the effects of, a pesticide.
b See environmental resistance.
3 (in immunology) The degree of immunity to infection that an animal possesses.