The effect of temperature on the interaction of Haemophilus ducreyi with human epithelial cells

Abstract

To investigate if temperature affects the interaction of Haemophilus ducreyi with human epithelial cells, nine strains were used to evaluate the adhesion kinetics of the organism at 338C and 378C. The effect of the free toxin on the epithelial cells at those temperatures was also assessed. The cyto-adherence kinetics of H. ducreyi to the epithelial cells was signi®cantly greater at 338C (10 times more) than at 378C in all seven clinical isolates tested. There was a signi®cant difference in cell-associated H. ducreyi at 338C as compared with 378C. Control strains showed similar adhesion properties at both temperatures. However, the virulent strain CIP542 adhered in larger amounts than the avirulent strain A77. Electron microscopy revealed that there was more tissue necrosis at the lower than the higher temperature. The effect of the free toxin was the same at each temperature. However, strain A77 had signi®cantly lower toxicity than strain CIP542 and the clinical isolates. These results suggest that H. ducreyi displays a temperature-dependent interaction with human epithelial cells, and this feature may play a role in the virulence of the organism in vivo. While the overall toxic effect of viable bacteria depends on the metabolic activity of the bacteria and is, therefore, higher at 338C than at 378C with the same initial inoculum, the effect of the extracted toxin at molecular level with ®xed concentrations is a temperatureindependent event.