Altered gene expression in Staphylococcus aureus upon interaction with human endothelial cells

Staphylococcus aureus is isolated from a substantial number of patients wit h infective endocarditis who are not known to have predisposing heart abnor malities. It has been suggested that the infection is initiated by the dire ct binding of S, aureus to human vascular endothelium. To determine the mut ual response of the endothelial cells and the bacteria, we studied the inte raction between S. aureus and human vascular endothelium. Scanning electron microscopic analyses showed that binding of S. aureus to human umbilical v ein endothelial cells (HUVEC) mainly occurred via thread-like protrusions e xtending from the cell surface, Bound bacteria appeared to be internalized via retraction of the protrusions into newly formed imaginations of the end othelial cell surface, The growth phase of S. aureus had a major impact on the interaction with HUVEC. Logarithmically growing bacteria showed increas ed binding to, and were more readily internalized by, HUVEC compared to sta tionary-phase bacteria. To assess the bacterial response to the cellular en vironment, an expression library of S, aureus was used to identify genes wh ose expression was induced after 4 h of exposure to HUVEC. The identified g enes could be divided into different categories based on the functions of t he encoded proteins (transport, catabolism, biosynthesis, and DNA repair). Further analyses of five of the S, aureus transposon crones showed that HUV EC as well as human serum are stimuli for triggering gene expression in S. aureus.