IAI Accepts, published online ahead of print on 29 June 2009

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Infect. Immun. doi:10.1128/IAI.01478-08
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Staphylococcal -toxin is not sufficient to mediate escape from phagolysosomes in upper airway epithelial cells

Bernd Giese, Silvia Dittmann, Kerstin Paprotka, Katja Levin, Annett Weltrowski, Diana Biehler, Thiên-Trí Lâm, Bhanu Sinha, and Martin J. Fraunholz^*

Competence Center for Functional Genomics, Ernst-Moritz-Arndt University, F.-L.-Jahnstrasse 15, D-17487 Greifswald, Germany; Inst. of Hygiene and Microbiology, University of Würzburg, Josef-Schneider-Str. 2, Bldg. E1, D-97080 Würzburg, Germany

^* To whom correspondence should be addressed. Email: Martin.Fraunholz{at}uni-greifswald.de.

Intracellular Staphylococcus aureus has been implicated in establishment of chronic infections. It is therefore an imperative to understand by which means S. aureus is able to survive within cells. Here we use two expression systems with a fluorescent readout to assay -toxin expression and function within phagolysosomes of infected upper airway epithelial cells: avirulent Staphylococcus carnosus TM300 and phenotypically -toxin negative S. aureus laboratory strains. CFU recovery assays suggest that presence of -toxin is not beneficial for intracellular survival of the recombinant Staphylococcus strains. This finding was corroborated by immunofluorescence studies: whereas S. carnosus and S. aureus are able to deliver S. aureus -toxin to lumina of host cell phagolysosomes, the membrane integrity of these organelles was not affected. -toxin expressing strains were exclusively detected within LAMP1-YFP-positive vesicles. Measurements of intraphagosomal pH illustrated that all infected phagolysosomes acidified regardless of -toxin expression. By contrast, S. aureus expressing LLO leads to breakdown of the phagolysosomal membrane as indicated by staphylococci that are not associated with LAMP1-YFP-decorated vesicles and that do not reside within an acidic cellular environment. Thus, our results suggest that staphylococcal -toxin is not sufficient to mediate phagolysosomal escape in upper airway epithelial cells.

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