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Pathogenic mechanisms of methicillin-resistant Staphylococcus aureus

Abstract number: P1046

Haggar A., Nguyen Hoang A., Svensson M., Arakere G., Norrby-Teglund A.

Objective: Community-associated (CA)-MRSA has been reported in association with highly aggressive infections, including necrotizing soft tissue or lung infections as well as septic shock. Here we have studied pathogenic responses elicited by MRSA isolates in human in vitro cell and tissue model systems.

Methods: CA-MRSA isolates (n = 17) collected in Bangalore were characterized with respect to agr type, superantigen gene profile and presence of the Panton-Valentine Leukocidin gene (PVL). Seven isolates with matched agr type, but varying toxin profiles, were selected for functional analyses and toxin-containing supernatants (SUPs) were prepared from stationary phase cultures. These SUPs were tested for ability to induce proliferation of peripheral blood mononuclear cells, and for cytotoxic (epithelial damage, HMGB-1 release) and/or inflammatory effects (IL8 expression) in a 3D organotypic lung tissue model. The latter analyses were done by immunostaining and in situ image analyses (ACIA) of SUP-exposed tissue.

Results: The proliferation assay showed that isolates clustered according to their agr type. Type I and II strains induced significantly stronger proliferation than did agr type III and IV isolates (ANOVA, p = 0.02). In fact, agr III and IV isolates induced a strong cytoxic response over a broad concentration range. The cytotoxicity could not be related to PVL-positivity, as the most cytoxic strain was PVL-negative. Western blot analyses of SUPs revealed higher amounts of a-hemolysin in cytotoxic, as compared to mitogenic, SUPs.

Two agr type II mitogenic isolates and three cytotoxic isolates (agr III and IV) were further tested in the lung tissue model. SUPs were added on the apical side of the epithelial layer in the tissue model and after 24 h of exposure the tissue was analyzed for IL-8 and HMGB-1. HMGB-1 was markedly increased in tissues exposed to the cytotoxic SUPs (ACIA=38–40) whereas tissue exposed to mitogenic SUPs was equal to control tissue (ACIA=19–23). IL-8 was upregulated in all tissues exposed to the SUPs (ACIA=20–45) as compared to unstimulated control tissue (ACIA=11).

Conclusion: Our findings reveal striking differences in mitogenic versus cytotoxic functions of MRSA isolates of varying agr types. These functional differences were also reflected in the responses elicited in the human lung tissue model. Furthermore, the data implicates a-hemolysin, rather than PVL, in these responses.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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