Many microorganisms exhibit antibiotic resistance to one or more antibiotics. This becomes an issue when the microorganism causes a disease, whether that disease affects humans, plants or animals. Such microorganisms can fall into the category of bacteria, virus, or multicellular parasite. Although some diseases are due to prions, they do not follow the same rules for antibiotic reactions, so I won't cover those.

Diseases are resistant to an antibiotic due to a genetic trait. In some cases, it requires as little as one gene to create a resistance to an antibiotic. Since it is a genetic trait, it is inherited from generation to generation in that disease. This trait may make the disease slightly more resistant to the antibiotic, or it may make it entirely immune, depending on how the specific antibiotic works. This fact is used in the genetic modification of bacteria and viruses; when a specific gene is inserted into the microorganism, it is accompanied by another gene for resistance to an antibiotic. Therefore, when that antibiotic is applied, only the genetically modified microorganisms are still there.

But how does a disease which isn't resistant to an antibiotic become resistant?

Now, two organisms will rarely be genetically identical. Although a bacteria reproduces by dividing into two copies of itself, bacteria can alter their own genetic structure within their lifetime by absorbing genetic material from other bacteria in packets called plasmids. Similarly, ionizing chemicals and various chemicals can cause mutations by altering an organisms genetic structure.

Therefore, in any mass of disease-causing microorganisms, there is a great deal of minor genetic variation, even if they are all the descendants of a single common ancestor. This genetic diversity is what creates the potential for genetic selection, a form of evolution. When an antibiotic is introduced into an environment housing the microorganisms which are not resistant to the antibiotic, it will kill or deactivate most or all of them. However, if even one of those microorganisms survives due to genetic differences that make it resistant to the antibiotic, it can reproduce itself again to be even more dangerous, because most or all of its descendants will have inherited the genetic resistance to that antibiotic.

Over time, that antibiotic will become less useful against that disease, and another antibiotic will have to be used. Eventually, after passing through many hosts and suffering and surviving the effects of multiple antibiotics, such a disease may have multiple resistances, making it a "super-bug," a nick-name for a disease that resists most conventional antibiotics. Such strains of diseases are, naturally, very dangerous.

The diseases which most easily form antibiotic resistance are those with a broad number of genetic variations (perhaps because it has a large genome, perhaps because it is easily mutated, or perhaps because it readily shares genetic material with other bacteria). The speed at which a bacterium reproduces is also an important factor. Bacteria vary widely in their speed of reproduction. Those which reproduce quickly will also evolve into new strains quickly, and are therefore more likely to develop antibiotic resistance.

A great deal of work is being done in laboratories around the world now to research ways to combat antibiotic resistance in diseases. Some involve creating antibiotics which don't lend themselves as easily to forming resistance. Other tactics involve attacks on the microorganisms at the genetic level. On the medical battleground, the battle continues.

Learn more about this author, Glen R. Taylor.
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