Thoughts on the evolution of strategies used by bacteria for evasion of host defenses.

The detailed study of the molecular biology of the mechanisms that pathogenic organisms employ to successfully parasitize their hosts has been very productive. An important part of the microbe's armamentarium is the ability to partially or totally evade one or more of the normal defenses of the host. While it is obvious that the molecular entities that produce these effects have an evolutionary history, as yet little attention has been devoted to this aspect. The study of the selective conditions that have given rise to a particular pathogenic property affords important perspectives on the process of mutual adaptation of the host and the parasite.