drug resistance

Bacteria are able to become resistant to antibiotics:

  • Millions of germs of a given species may inhabit the patient's body.
  • As they multiply, new mutations of the genetic code give rise to strains that are less resistant to a given antibiotic.
  • The susceptible germs are killed off - the stronger survive.
  • Eventually enough of the descendants can resist the antibiotic's effects to cause problems of treatment failure.

How much of a problem is this in real life? Well, it is a growing problem, but certainly not to the degree that tabloid journalism has made it appear. It is the best argument for respecting your doctor's judgement if he or she decides to hold off on the antibiotics altogether for illnesses that are clearly viral or can be treated without systemic antibiotics (for example mupiricin - Bactroban® for impetigo rather than an oral antibiotic). It is also a good argument for not pressuring the doctor for broader spectrum antibiotics ("Give him the strongest one, doc - I need him well tomorrow for his game!").

Can your child become "immune to antibiotics?" Parents usually misunderstand what physicians are talking about when they mention drug resistance in bacteria. Some further clarification of the issues of resistance is in order.

First, realise that it is the germ that becomes resistant to the drug, not the patient. Resistance can only develop in the 'target' of the medication. A person who chronically takes the same antihistamine may develop tolerance ('resistance')to it's effects. That is because as the antihistamine works it effects on the person. An antibiotic works its effects on bacterial germs, not on the person taking the antibiotic. So patients cannot become immune to an antibiotic, but that patient's germs can become immune to the antibiotic.

Next, resistance to one antibiotic drug can arise as a consequence of taking another antibiotic. For example, penicillin resistance is most easily produced in the pneumococcus bacterium by broad spectrum cephalosporins (related to penicillin in chemical structure and action).

Finally and most perversely, bacteria are able to teach each other how to be resistant to antibiotics. By exchange of genetic material, germs can transmit resistance through the same species and even from species to species.

Some antibiotic resistance is not caused as much by antibiotic use or overuse in humans as much as that in animals. Certain antibiotics are routinely fed to poultry, as an example, to prevent loss of the birds to disease before slaughter. The bacteria resident in these birds become resistant, and are disseminated into the world via the poultry carcasses. From those avian species of bacteria, resistance to the antibiotic spreads to other species of bacteria related to humans.

In addition to resistance caused by the use of antibiotics, there can be resistance caused by the presence of certain man-made chemical substances in the environment. For example, the recent emergence of vancomycin resistant enterococci is thought to have arisen from the exposure of the bacteria to avoparcin, a chemical growth-promoter for livestock with the same general molecular structure as the antibiotic. It is used extensively in Europe.

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