Production of listeriolysin O by Listeria monocytogenes (Scott A) under heat-shock conditions

Early stationary phase cells of Listeria monocytogenes (Scott A) were exami ned to determine the effect of heat-shock on the production of listeriolysi n O (LLO) during and after resuscitation at 37 degrees C. Cells were subjec ted to a heat-shock at 48 degrees C for 1 h. Intracellular and extracellula r proteins of the heat-shocked cells were assayed for LLO using a microtite r plate hemolysis assay and analyzed by sodium dodecyl sulfate-polyacrylami de gel electrophoresis (SDS-PAGE) and immunoblotting. Our results showed th at significant amounts of LLO are synthesized under heat-shock conditions t hat are not detected in the extracellular medium by a functional assay. Thi s situation is evident by the absence of hemolytic activity immediately aft er heat-shock, and may be due to either a lack of excretion or inactivation of the LLO at 48 degrees C once outside the cell. By studying the intracel lular and extracellular proteins using SDS-PAGE and immunoblots of the heat -shocked cells, we substantiated an absence of excretion as an operating me chanism. Heat-shocked cells resumed LLO production within 2-4 h of resuscit ation at 37 degrees C, achieving an activity level 2-fold higher compared t o the controls and 4-fold higher compared to cells immediately after heat-s hock. Most likely, the LLO excreted must have been from LLO accumulated in the cells during heat-shock. (C) 1999 Elsevier Science B.V. All rights rese rved.