Overuse of antibiotics is not the only reason for organisms to develop resistance it is merely one factor. Many antibiotics work to either prevent the formation of a cell wall or block other key metabolic functions. Different classes of antibiotics will generally work on different types of bacteria.

Bacteria can gain resistance in at least two ways:

First, most antibiotics will not “kill” or prevent the growth of all its’ intended targets. Bacteria will have range of susceptibility. The goal is to reduce the numbers substantially so that the body’s’ own defenses can kill the remaining organisms. The remaining organisms, which either had greater resistance (genetic or mechanism development) or may have been in parts of the body in which the antibiotic was sub-therapeutic, survive. These bacteria multiply, with future generations, which have developed genetic resistance or develop mechanism to increase their chances of survival (slime, adherence factors).

The other way is for one type of bacteria, which has a natural resistance to a certain class of antibiotic, becoming infected with a bacterial phage (a virus that infects bacteria). The bacterial phage “latches” on the genetic material responsible for resistance to a particular class of antibiotics and infects the bacteria without that natural resistance and imparts the newly acquired genetic resistance factor to the new bacterial host. Subsequent generations of these altered bacteria will now also possess the antibiotic resistance.


Sorry if this is confusing or unclear, it is a lot easer to explain then to write.

Pete