Staphylococcal strains vary greatly in their ability to induce an inflammatory response in endothelial cells.
BACKGROUND
Staphylococcus aureus is an important human pathogen of endovascular diseases that can take an acute destructive course and/or develop into a chronic infection with a high rate of relapse. Despite good activity of the appropriate antimicrobial substances in vitro, these infections are often difficult to treat, perhaps because of the complex infection process of endovascular tissue.


METHODS
We used the microarray technique to analyze the response of endothelial cells to different S. aureus strains, including highly virulent isolates (6850 and ST239); the Cowan I strain, which has a nonfunctioning accessory gene regulator (agr) quorum-sensing system; and various clinical isolates.


RESULTS
All tested strains were equally invasive in endothelial cells and were found intracellularly, but they differed greatly in their ability to induce inflammation. Wild-type isolates (6850 and ST239) up-regulated a huge number of genes, including many genes involved in innate immunity. By contrast, Cowan I, which failed to express important virulence factors related to the agr system (eg, alpha-toxin and proteases), did not induce these dramatic changes in endothelial gene expression. Similar results were obtained with clinical isolates.


CONCLUSIONS
Given that agr-defective strains are commonly recovered during colonization and infection, agr deficiency might represent a strategy of S. aureus to hide intracellularly without provoking the host immune system and causing relapsing infections.
Institute of Medical Microbiology, University Hospital of Münster, Domagkstrasse 10, D-48149 Münster, Germany.
Matthias
M
Grundmeier
Lorena
L
Tuchscherr
Michaela
M
Brück
Dorothee
D
Viemann
Johannes
J
Roth
Edith
E
Willscher
Karsten
K
Becker
Georg
G
Peters
Bettina
B
Löffler
D001426:Bacterial Proteins / Q000502:physiology; D042783:Endothelial Cells / Q000382:microbiology* / Q000473:pathology; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000235:genetics / Q000472:pathogenicity*; D015534:Trans-Activators / Q000502:physiology; D014471:Umbilical Veins; D037521:Virulence Factors / Q000235:genetics
C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D015534:Trans-Activators; D037521:Virulence Factors