Introduction To Antibiotics

Humans, and our domestic animals, can serve as hosts to a wide variety of disease-causing organisms (pathogens):

* bacteria
* viruses
* fungi
* protozoans
* helminths (worms).

This page will examine only those chemical agents that are used to combat bacterial pathogens.
The Problem
There are many chemicals that are lethal to bacteria — cyanide does a good job — but they cannot be used to cure infections because they are lethal to the host as well. The problem, then, is to find substances that attack a metabolic pathway found in the bacterium but not in the host. This is not an insurmountable problem for bacterial pathogens because they differ in many respects from eukaryotes.
The Solution

* Natural products. A number of natural products, penicillin for example, have been discovered that are antibiotics suitable for therapy. They were originally discovered as secretions of fungi or soil bacteria. Soils are complex ecosystems, and it is not surprising that its inhabitants have evolved chemical defenses against each other.

# Semi-synthetic products. These are natural products that have been chemically modified in the laboratory (and pharmaceutical facility) to

* improve the efficacy of the natural product
* reduce its side effects
* circumvent developing resistance by the targeted bacteria
* expand the range of bacteria that can be treated with it