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 grow. 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 antibiotic - this is called survival of the fittest. This more resistant microbe will grow better than all the others when the antibiotic is present 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.

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.