[Fast and slow genome rearrangements: molecular and genetic mechanisms of changes in virulence]

Different mechanisms of virulence changes at the molecular and populational levels are discussed. The methodology and mechanisms of Streptococcus pyogenes variability are analysed. The views of the adaptive role played by insertion sequences are developed, and the design of an epidemiologico-genetic experiment is proposed, which consists in obtaining highly virulent insertion mutants and testing their properties.