This occurs when bacteria change over time. The changed bacteria are no longer killed by medicines that were once effective, making infections harder to treat and increasing the risk of disease spread, severe illness and death. AMR also occurs naturally, but is more important when it is a result of AMU, especially inappropriate and excessive use.

AMR can increase due to a range of factors that increase the risk of spread of bacterial infections, such as poor infection prevention and control in healthcare settings, lack of access to water, poor sanitation and hygiene facilities, poor nutrition, and other factors.

AMR refers to resistance in all types of infection (bacterial, viral, fungal, etc.) but this course focuses predominantly on bacterial AMR.