For over five decades, the world was thought to have conquered infectious diseases like meningitis and tuberculosis with a vast array of 'wonder' drugs: antibiotics. But at the same time, scientists have known since the dawn of the antibiotic age that the more an antibiotic is used, the quicker it becomes useless. In recent years concern has increased that the antibiotic era might be coming to an end.
Bacteria are found in more varied habitats and environments than any other living thing. The adult human body itself composes some 1014 cells, but only 10% of these are human. The remaining are bacteria, fungi, protozoa, worms and even insects that make up the normal flora (Hart, 1998). Of course, bacteria also cause diseases, ranging from ear infections (otitis media) to meningitis. However, antibiotics are used to fight infections that are caused by bacteria. They might, for example, inhibit the bacteria's ability to turn glucose into energy, or the bacteria's ability to construct its cell wall, thus impairing its ability to reproduce. Unfortunately, over the last five decades, the mounting increase in the use of antibiotics has delivered a selection unprecedented in the history of evolution (Levy, 1992). The powerful killing and growth inhibitory effects of antibiotics have reduced the numbers of susceptible strains, leading to the propagation of resistant variants.
There are a number of factors that can influence whether a bacterium is, or will become, insensitive to an antibiotic. The two main ones are the prevalence of resistant genes and the extent of antibiotic use and/or exposure.
In the first case, the bacteria will be unaffected and will multiply normally. It should be noted that antibiotic-resistant pathogens are not more virulent than susceptible ones: the same number of virulent and susceptible bacterial cells are required to produce disease, but the resistant forms are simply harder to destroy and many possessed resistant genes even before commercial antibiotics came into use (Levy, 1999).
Gene exchange between bacterial cells may take place in three ways. Firstly, bacterial cells are able to interchange their genes with ease in a form of bacterial sex, which occurs irrespective of the species (Levy, APUA). Secondly, resistance genes normally found on plasmids can be transferred by viruses from one bacterial cell and to another. Thirdly, a dead bacterium leaves a legacy behind. After a bacterium dies and liberates its contents into the environment, another will occasionally cannibalise a liberated gene for itself. Bacteria recycle their genes.
