Possible virulence factors of Staphylococcus aureus in a mouse septic model

Twenty clinical isolates of Staphylococcus aureus were examined to elucidat e the virulence factors which are directly related to lethality in a mouse septic model. Heat or Formalin treatment of the organism abolished the leth al activity of the live organism during challenge intravenously administere d via the tail vein. Nevertheless, injection of tell times concentrated cul ture supernatant fluid (SUP) showed lethal activity in the mouse. However. there was no lethality when SUP was heated at 60 degrees C for 15 min. To e xamine variations of SUP lethality among strains, we collected 20 strains o f S. aureus from four different hospitals. Then, we compared several factor s for SUP lethality, which were the extracellular toxins and enzymes, such as toxic shock syndrome toxin 1, enterotoxin A, B, D, and hemolysins (alpha ,beta,gamma), and also cytotoxic activity to human polymorphonuclear leukoc ytes and Vero cells. No difference was found among these factors except cyt otoxic activity to Vero cells. Furthermore, we compared two strains in a mo use septic model according to the grade of bacteremia and lethal events. We found that mortality was higher with challenge by the strain whose SUP was lethal in comparison to the strain whose SUP was not lethal, even though t he viable bacteria counts in the septic blood in both strains were not sign ificantly different. This strongly supports the possibility that extracellu lar products, not the cell wall components, of S. aureus play the key role in the lethal evens in this mouse septic model. In addition. among the extr acellular products, those which have cytotoxic activity to Vero cells may c ontribute to the lethality in sepsis caused by S. aureus in this murine mod el. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.