Antibiotics

Antibiotics

A variety of infectious diseases are caused by bacteria. Some bacterial infections can be treated using compounds that are collectively known as anti-biotics. Antibiotics act only on bacteria, and are not effective against viruses.

The presence of antibiotics in blood or tissue samples obtained after death (post-mortem samples) can be an important clue to the presence of an infection in the deceased.

The unique chemical structure of an antibiotic, relative to the natural tissue, can allow the compound to be detected. For example, cephalosporin antibiotics have been successfully detected in post-mortem samples using the technique of high-pressure liquid chromatography , which separates compounds based on their differing rates of movement through a porous support material.

Antibiotics can be naturally produced. For example, the first antibiotic discovered (penicillin; discovered in 1928 by Sir Alexander Fleming) is produced by a species of a mold microorganism. There are a variety of different naturally produced antibiotics, while many other antibiotics have been chemically produced.

Prior to the discovery of penicillin there were few effective treatments to battle or prevent bacterial infections. Pneumonia, tuberculosis, and typhoid fever were virtually untreatable. And, in those persons whose immune systems were not functioning properly, even normally minor bacterial infections could prove life-threatening.

In nature, antibiotics (or antimicrobials) help protect a eukaryotic cell (i.e., plant cell) or bacteria from invading bacteria (in some environments, bacteria may be in competition). In the laboratory, this protective advantage is evident as the inhibition of growth of bacteria in the presence of the antibiotic-producing species. Screening for antimicrobial activity is done on preparations that are obtained from a variety of sources (soil, water, plant extracts). This screening can be automated so that thousands of samples can be processed each day.

The chemical synthesis of antibiotics is now very sophisticated. The antibiotic can be tailored to affect a specific target on the bacterial cell. Three-dimensional modeling of the bacterial surface and protein molecules is an important aid to antibiotic design.

Penicillin is in a class of antibiotics called beta-lactam antibiotics. The name refers to the chemical ring that is part of the molecule. Other classes of antibiotics include the tetracyclines, aminoglycosides, rifamycins, quinolones, and sulphonamides. The action of these antibiotics is varied. The targets of the antibiotics are different. Some antibiotics disrupt and weaken the cell wall of bacteria (i.e., beta-lactam antibiotics), which causes the bacteria to rupture and die. Other antibiotics disrupt enzymes that are vital for bacterial survival (aminoglycoside antibiotics). Still other antibiotics target genetic material and stop the replication of deoxyribonucleic acid (DNA ) (i.e., quinolone antibiotics).

Antibiotics can also vary in the bacteria they affect. Some antibiotics kill only a few related types of bacteria and are referred to as narrow-spectrum antibiotics. Other antibiotics such as penicillin kill a variety of different bacteria. These are the broad-spectrum antibiotics.

Following the discovery of penicillin, many different naturally occurring antibiotics were discovered and still many others were synthesized. They were extremely successful in reducing many infectious diseases. Indeed, in the 1970s the prevailing view was that infectious diseases were a thing of the past. However, beginning in the 1970s and continuing to the present day, resistance to antibiotics is developing.

As of 2005, the problem of antibiotic resistance is so severe that many physicians and scientists think that the twenty-first century will initiate the "post antibiotic era." In other words, the use of antibiotics to control infectious bacterial disease will no longer be an effective strategy.

Resistance to a specific antibiotic or a class of antibiotics can develop when an antibiotic is overused or misused. If an antibiotic is used properly to treat an infection, then all the infectious bacteria should be killed directly, or weakened such that the host's immune response will kill them. However, if the antibiotic concentration is too low, the bacteria may be weakened but not killed. The same thing can happen if antibiotic therapy is stopped too soon. The surviving bacteria may have acquired resistance, which can be genetically transferred to subsequent generations of bacteria. For example, many strains of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, are resistant to one or more of the antibiotics currently used to treat the lung infection. Some strains of the Staphylococcus aureus bacteria that causes boils, pneumonia, or bloodstream infections, are resistant to most (and with one strain, all) antibiotics.

see also Anthrax; Bioterrorism; L-Gel decontamination reagent; Pathogens.