Antimicrobial resistance is the ability of microbes, such as bacteria, viruses, parasites or fungi, to grow in the presence of a chemical (drug) that would normally kill it or limit its growth.
AAPA Policy on Antimicrobial Resistance
Misuse and overuse of antimicrobial agents have exacerbated problems associated with resistant microbes.
Sources of misuse and overuse include inappropriate prescribing by clinicians; expectation, demand for, and poor compliance by patients; and availability of antimicrobial agents without a prescription in many developing countries.
Read more in AAPA's policy paper on antimicrobial resistance [PDF].