TAILIEUCHUNG - Chapter 129. Staphylococcal Infections (Part 3)

Regulation of Virulence Gene Expression In both toxin-mediated and non-toxin-mediated diseases due to S. aureus, the expression of virulence determinants associated with infection depends on a series of regulatory genes [., accessory gene regulator (agr) and staphylococcal accessory regulator (sar)] that coordinately control the expression of many virulence genes. The regulatory gene agr is part of a quorum-sensing signal transduction pathway that senses and responds to bacterial density. Staphylococcal surface proteins are synthesized during the bacterial exponential growth phase in vitro. In contrast, many secreted proteins, such as α toxin, the enterotoxins, and assorted enzymes, are released during the postexponential. | Chapter 129. Staphylococcal Infections Part 3 Regulation of Virulence Gene Expression In both toxin-mediated and non-toxin-mediated diseases due to S. aureus the expression of virulence determinants associated with infection depends on a series of regulatory genes . accessory gene regulator agr and staphylococcal accessory regulator sar that coordinately control the expression of many virulence genes. The regulatory gene agr is part of a quorum-sensing signal transduction pathway that senses and responds to bacterial density. Staphylococcal surface proteins are synthesized during the bacterial exponential growth phase in vitro. In contrast many secreted proteins such as a toxin the enterotoxins and assorted enzymes are released during the postexponential growth phase. It has been hypothesized that these regulatory genes serve a similar function in vivo. Successful invasion requires the sequential expression of these different bacterial elements. Bacterial adhesins are needed to initiate colonization of host tissue surfaces. The subsequent release of various enzymes enables the colony to obtain nutritional support and permits bacteria to spread to adjacent tissues. Studies with mutant strains in which these regulatory genes are inactivated show reduced virulence in several animal models of S. aureus infection. Pathogenesis of Invasive 5. aureus Infection Staphylococci are opportunists. For these organisms to invade the host and cause infection some or all of the following steps are necessary inoculation and local colonization of tissue surfaces invasion evasion of the host response and metastatic spread. The initiation of staphylococcal infection requires a breach in cutaneous or mucosal barriers. Colonizing strains or strains transferred from other individuals are inoculated into damaged skin a wound or the bloodstream. Recurrences of S. aureus infections are common apparently because of the capacity of these pathogens to survive to persist in a quiescent state

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