The term antibiotic resistance refers to the ability of bacteria and other micro-organisms to withstand the effects of an antibiotic to which it was previously sensitive. Consequently, these resistant organisms are not inhibited by antibiotics at the serum/tissue concentrations achievable after normal dosing of the drug. In contrast to other drugs, antibiotics are unique in that the use of these agents in one patient can influence future efficacy – not only in the same patient but also for other patients and potentially a whole population.
The widespread use of antibiotics has exerted selective resistance pressure, and this, coupled with the transfer of microorganisms between people, has led to (often rapid) emergence of antibiotic resistance. Only a low level of native genetic antibiotic resistance exists in micro-organisms, but the abundance and variation in resistance genes in bacteria became established after extensive clinical use of man-made antibiotics in various settings.