Abstract
The array of mechanisms that bacteria possess to withstand extreme conditions and to resist harmful drugs and other toxic agents compounds is fascinating. Use of antibacterial medicines over the last 60 years have triggered a combination of genetic and biochemical mechanisms within the bacteria to secure their survival in otherwise lethal environments. Bacterial clones with natural and acquired resistance have continuously been selected as an evolutionary response to the use of antibiotics. Resistance can be acquired as a result of genetic events causing alterations in the pre-existing bacterial genome such as point mutations and gene amplifications. The other major mechanism is horizontal gene transfer between bacteria both within and between species, where transposons, integrons or plasmids are introduced into an organism. The successive introduction of new antibiotics has catalysed the accumulation of resistance mechanisms that travel between microbes, creating clones with multiresistant properties.