[Genetic regulatory mechanisms of bacterial virulence]

Bacterial virulence is due to the action of different virulence factors (e.g. adhesins, toxins, capsules). Virulence factors are encoded by special genes termed as virulence genes or virulence determinants. The degree of virulence of one particular bacterial strain depends on the activity of the corresponding virulence genes. Several mechanisms are involved in the regulation of activity of virulence determinants: plasmids and bacteriophages may be received or lost and chromosomal sequences may be deleted. Such processes are directly responsible for the presence or absence of virulence genes in the bacterial genome. Programmed genetic rearrangements may lead to a switch of promoter sequences and are therefore responsible for a variation of virulence expression. "Jumping" of DNA sequences (transposition) and subsequent recombinational events may also cause antigenic variation of virulence factors. In addition frame shift mutations may influence the expression of virulence genes. Transregulatory factors may also influence the expression of virulence factors of pathogenic bacteria. These systems positively influence the expression of different virulence factors in a coordinative manner. They can be triggered by environmental signals.