What is an antibiotic?
Doxycycline is one of the tetracyclines, a class of antibiotics that has had great success in the fight against bacterial infections. To understand how this fight is won, the first task is to explain exactly what an antibiotic is and does. The word first appeared in the 1940s and it refers to a substance produced by one bacterium or fungus that prevents the growth of another bacterium. It reflects the old saying, “Fight fire with fire.” This refers to the use of fire breaks where you produce a controlled burn of one small area in the path of a larger advancing fire. So when the larger fire arrives, it runs out of fuel and dies. Applying this to medicine, research chemists developed a method of culturing bacteria or fungi that would produce a substance capable of killing or preventing other bacteria from reproducing. Penicillin, for example, is produced from a fungus while streptomycin is derived from the bacterium called Streptomyces. Thus, contrary to popular belief, antibiotics are “natural” in the sense that they are derived from bacteria or fungi occurring in the natural world. They are distinguished from drugs that are entirely artificial. For example, the sulphonamides have an antibacterial effect but are completely synthetic.
The continuing research and development work on antibiotics has paralleled the work in Eastern Europe and Russia to develop phages which are viruses that infect bacteria. This represents a different delivery system for killing or preventing the reproduction of bacteria. As more bacteria become resistant to antibiotics, more in the West are considering a switch to phages. It is hoped that new phages can be developed as a biocide for environmental surfaces in hospitals and other residential institutions to prevent the spread of methicillin-resistant Staphylococcus aureus (MRSA), C. Difficile and other life-threatening infections.
While work continues into the use of phages, doctors continue to rely on antibiotics which are divided into two classes depending on whether they are narrow or broad. A narrow antibiotic only targets very specific bacteria. A broad antibiotic is effective against a range of bacteria. Doxycycline is in the broad range.
| Coming to the second question of how antibiotics work, some are bactericidal, i.e. they kill bacteria, whereas others are bacteriostatic, i.e. they prevent the bacteria from dividing and, as a result they die of old age. The problem is that, the more a bacterium is exposed to an antibiotic, the more likely it is to develop a resistance. This explains why, when you are prescribed an antibiotic, your doctor will always instruct you to continue taking the tablets until the end of the recommended course of treatment. You have to take the tablets even though you feel well. The reason? You are taking it to continue killing as many of the bacteria in your body as possible. The greater the number that survive, the more survivors there will be with resistance. |
But there is a further problem. For decades, the farming industry has administered large quantities of antibiotics to the animals you eat. So instead of only consuming antibiotics when you are sick, there is continuous ingestion if you eat meat. As a result, many of the different strains of bacteria in the animal world have built up resistance. To prevent them from joining you, it is necessary to cook meat thoroughly. Heat kills most of bacteria that are dangerous to humans. If you eat meat rare, there is a risk of antibiotic-resistant bacteria taking up residence in your gut. Unfortunately, heat does not “kill” antibiotics so the bacteria in your body are continuously exposed to a low level dose of broad spectrum antibiotics all the time. This explains why there are now an increasing number of bacteria which are resistant to antibiotics.
