Salmonella pathogenicity islands: big virulence in small packages

Reflecting a complex set of interactions with its host, Salmonella spp. req uire multiple genes for full virulence. Many of these genes are found in 'p athogenicity islands' in the chromosome. Salmonella typhimurium possesses a t least five such pathogenicity islands (SPI), which confer specific virule nce traits and may have been acquired by horizontal transfer from other org anisms. We highlight recent progress in characterizing these SPIs and the f unction of some of their genes. The role of virulence genes found on a high ly conserved plasmid is also discussed. Collectively, these packages of vir ulence cassettes are essential for Salmonella pathogenesis. (C) 2000 Editio ns scientifiques et medicales Elsevier SAS.