However, through massive and increasing use of antimicrobials in humans, animals, fish and in agriculture, a resistance problem has been created that is rapidly moving to the forefront of public health concerns. The microbes which survive are those that carry genes for resistance to antimicrobial agents and, in the medical setting, a resistant microbe is one which is not killed by an antimicrobial agent after a standard course of treatment. Antimicrobial agents are also used in agriculture such as livestock and crop production, as well as in fish farming and to treat and control animal diseases and enhance growth and yield. All these uses increase the total selective pressure exerted on the microbial world and encourage the emergence of resistance. Bacteria are particularly efficient at enhancing the effects of resistance, not only because of their ability to multiply very rapidly but also because they can transfer their resistance genes to other strains.
Resistant microbes can spread easily from person to person.
The enormous increase in international travel in recent years means that individuals may be exposed to resistant microbes in one country and carry them to other countries, where resistance can then spread. For example, resistant strains of gonorrhoea that originated in Asia and Africa, have now spread throughout the world. Resistance in bacteria is most commonly detected during standard laboratory investigations to establish the cause of a patient's infection and the best choice of treatment. Detection depends on the collection of specimens from the patient, and on the availability of laboratory facilities for isolation, identification and susceptibility testing of the infecting microbe. This takes time and money and thus is often foregone.