Staphylococcus aureus

In S. aureus, a derivative of the eukaryotic mariner transposon, delivered on a ther-mosensitive plasmid, was used to generate an archived library of 10 325 clones, of which 9540 were transposon insertion mutants [28]. Transposon insertion sites were amplified by inverse PCR and directly sequenced. Unfortunately, since mutagenesis was performed in the Newman strain, whose genome sequence is not known, the sequencing results could not be fully exploited. Nevertheless, using available S. aureus genome sequences, it was possible to map 8450 transpo-son insertions sites and to establish that 6917 of these were within coding sequences. Insertions occurred in at least 1812 different ORFs, which probably represent some 67% of the coding sequences in the Newman strain genome. However, this study illustrates perfectly how these resources may lead to a comprehensive understanding of the mechanisms of pathogenesis by leading to the identification of all the determinants of virulence. Indeed, 1736 mutants with insertions in different ORFs were screened in triplicate in the nematode Caenor-habditis elegans as model host in order to identify S. aureus virulence genes, which identified 71 genes important for pathogenicity. Among the 30 genes of unknown function, some were also important virulence factors in a murine model of infection.

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