Antibiotic

Antibiotics are molecules that kill (bactericidal) or reduce the growth (bacteriostatic) of bacteria.

Role of antibiotics

Antibiotics are used in medicine (and in veterinary medicine) to combat bacterial infections and must be chosen according to their efficacy on the bacterium to be treated. This can be tested with an antibiotic sensitivity profile.

Origin of antibiotics

Antibiotics used in medicine are produced from micro-organism cultures or are entirely synthetic medicines. Alexander Fleming discovered the first of these (penicillin) by chance in a fungus Penicillium glaucum.

An antibiotic is a substance which can reduce or stop the multiplication of bacteria. The medicine is a chemical compound produced by a micro-organism or from synthetic substances.

How do antibiotics act ?

There are a great many antibiotics that are divided into different families They are very effective against bacterial infections but have no action on viral infections. Some of these medicines inhibit the multiplication of bacteria. These are then called dits bacteriostatic. Others can destroy bacteria in which case they are called dits bactericidal. As we have seen, antibiotics must not be administered in viral infections. They are of no use in these situations. On the contrary, they risk pre-disposing development of bacterial resistance to these treatments. Finally, and again to avoid the development of bacterial resistance, the duration of prescribed treatment must be followed. The antibiotic must be continued even if the fever and symptoms disappear before the course of antibiotic is finished.

Families of antibiotics

There are many antibiotics, which can be classified into families according to their methods of action or molecular structure:

1. Bactericidal antibiotics

• the beta-lactams (such as penicillin) inhibit the synthesis of the bacterial cell wall;
• the aminoglycosides (such as streptomycin) interfere with the ribosome and prevent translation of messenger RNA into proteins;
• the imidazoles;
• the macrolides (such as erythromycin) block the 50S sub-unit of the prokaryotic ribosome by inhibiting its translocation or peptidyl transferase;
• the fosfomycins;
• the quinolones prevent replication of bacterial DNA by blocking DNA gyrase and topo-isomerase II;
• the glycopeptides inhibit formation of the bacterial wall by blocking the synthesis of peptidoglycans ;
• and the polypeptides.

2. The bacteriostatic antibiotics

• the phenicols (such as chloramphenicol) block the bacterial ribosome peptidyl transferase ;
• the tetracyclines inhibit binding of transfer RNA to the ribosome-messenger RNA complex and interfere with translation.