ALISTAIR J LAX
Many bacteria and higher eukaryotes live in harmony in a symbiotic relationship that benefits one or both of the partners. Indeed, we are colonised by
bacterial cells which outnumber our own cells ten to one. This amicable bacterial lifestyle contrasts with a pathogenic one, in which the bacterium causes
damage to its host. This is a potentially dangerous strategy for a bacterium,
because the provoked host is capable of fighting back. A pathogenic lifestyle
offers short-term gain. By outcompeting other bacteria within its host, the
bacterium can achieve local dominance and, by more widespread colonisation, expand its territory more globally. However, evolution has to balance
these advantages against the possibility that the bacterium is eliminated. The
latter could occur if the bacterium is too weak to prevent its destruction by
the strong host defences it has incited or if its potent virulence wipes out the
host and, thus, its source of food