What is antimicrobial resistance?

In the general sense, antimicrobial resistance means that an organism has either natural resistance (intrinsic resistance) to an antimicrobial, or has acquired a resistance mechanism (acquired resistance). In both healthcare and community settings, the development of resistance is usually due to selective pressure exerted by the widespread presence of antimicrobial drugs in the environment, together with the facilitated transfer of organisms (or their genetic material) within the environment.

The concept of resistance also applies to laboratory antimicrobial susceptibility testing and reporting (see Overview of interpreting microbiological testing results). Use of the term ‘resistant’ in susceptibility testing implies that the specified antimicrobial, when used to treat an infection at a specific site with a particular dose, is likely to fail.