what’s the science behind antimicrobial resistance?

amr naturally occurs by a process called natural selection. there is constant variation in all microbial populations as individuals are always making mistakes in replicating their genetic material as they multiply. this is called spontaneous mutation.  some of these mutations help an individual microbe to survive better than all the others in the presence of a certain antimicrobial - this is called survival of the fittest.

take treatment of a bacterial infection as an example: a more resistant bacterial cell survives better than all the others during antimicrobial treatment and takes over the population: the antibiotic has put selective pressure on the microbial population to become more resistant. this can also happen more quickly when whole genes or sets of genes that confer resistance are passed from one microbe to another. this is called horizontal gene transfer.

the same basic principles apply when viruses, fungi and parasites evolve resistance.

so, microbes are able to evolve and evade anything that puts selective pressure on them. this happens in all microbes, including the ones that aren’t harmful to humans.  amr is just microbes evolving by responding to the selective pressure that antimicrobials put on them.