Fig. 3.13 A Growth of S. aureus RN6390 in TSB-Medium. The sampling is indicated by an arrow and a letter in the respective growth curve. B, C Virulence factors of S. aureus RN6390 whose amount depends on the growth phase. The amount of the respective proteins at OD540 = 1 (green) of cells grown in TSB medium was compared with the amount of these proteins at higher optical densities

(red). B Virulence factors only present at low cell densities. C Virulence factors only present at high cell densities. In addition, the amount ofthe respective proteins in the wild type strain was compared to the amount of these proteins in various regulatory mutants (agr, sarA, sigB) known to be impaired in virulence. Proteins were stained with Sypro Ruby. (This figure also appears with the color plates.)

wild type and mutants in global regulators - transcriptomics to visualize the gene expression pattern and proteomics to visualize the protein secretion profile -might be the state-of-the-art approach to defining the expression of virulence genes, which is a very complex gene expression network. This network consists of many overlapping regulons expressed in a time-controlled manner to ensure the optimal pattern and level of the individual virulence factors at the different locations in the host. Infection models in combination with DNA array studies must be used to visualize the gene expression pattern in the host cell and in the para-

site, aiming at a more comprehensive picture of what is happening on both sides during the infection process.

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