Antibiotic Resistance - Causes

Causes

Although there were low levels of preexisting antibiotic-resistant bacteria before the widespread use of antibiotics, evolutionary pressure from their use has played a role in the development of muiltidrug resistance varieties and the spread of resistance between bacterial species. In medicine, the major problem of the emergence of resistant bacteria is due to misuse and overuse of antibiotics. In some countries, antibiotics are sold over the counter without a prescription, which also leads to the creation of resistant strains. Other practices contributing towards resistance include the addition of antibiotics to livestock feed. Household use of antibacterials in soaps and other products, although not clearly contributing to resistance, is also discouraged (as not being effective at infection control). Also unsound practices in the pharmaceutical manufacturing industry can contribute towards the likelihood of creating antibiotic-resistant strains. The procedures and clinical practice during the period of drug treatment are frequently flawed - usually no steps are taken to isolate the patient to prevent re-infection or infection by a new pathogen, negating the goal of complete destruction by the end of the course. (see Healthcare-associated infections and Infection control)

Certain antibiotic classes are highly associated with colonisation with "superbugs" (highly antibiotic resistant bacteria) compared to other antibiotic classes. The risk for colonisation increases if there is a lack of sensitivity (resistance) of the superbugs to the antibiotic used and high tissue penetration, as well as broad-spectrum activity against "good bacteria". In the case of MRSA, increased rates of MRSA infections are seen with glycopeptides, cephalosporins and especially quinolones. In the case of colonisation with Clostridium difficile the high risk antibiotics include cephalosporins and in particular quinolones and clindamycin.

Of antibiotics used in the United States in 1997, half were used in humans and half in animals.