Ultrastructural changes in HEp-2 cells treated with staphylococcal alpha-toxin

Effects of alpha-toxin of Staphylococcus aureus on the ciliary activity and ultrastructure of human nasal ciliated epithelial cells

OBJECTIVE

The in vitro effects of staphylococcal alpha-toxin on ciliary activity were investigated at different concentrations and exposure times.

STUDY DESIGN

Ciliated epithelial cells of the sphenoid sinus were taken from patients operated on for pituitary tumors. Video-computerized analysis technique and transmission electron microscopy were used to analyze the effects of the toxin on ciliary activity.

METHODS

Ciliary beat frequency (CBF) was measured in four different concentrations of alpha-toxin including 0.1, 1, 10, and 50 microg/mL. CBF was measured at 2, 4, 6, 12, 24, and 48 hours after administration of the toxin. To observe reversibility of the reduced ciliary activity, after 24-hour incubation in the media containing 10 microg/mL of alpha-toxin, the media were replaced with alpha-toxin-free media. The tissues were also processed for transmission electron microscopy to observe ultrastructural changes of the epithelial cells.

RESULTS

CBF increased significantly at 2-hour incubation and then decreased significantly after 12-hour incubation in 10 microg/mL of alpha-toxin (P< .05, repeated-measures ANOVA). The transmission electron microscopic findings showed mitochondrial swelling and a slight protrusion of the plasma membrane of the cilia. In toxin-free media, loss of ciliary activity was not recovered.

CONCLUSIONS

CBF increased at first, but with increasing incubation time ciliary movements decreased gradually and stopped eventually. This loss of CBF may be an irreversible change associated with ultrastructural changes in the mitochondria and the plasma membrane of the cilia.

The influence of bacterial exotoxins and endotoxins on the phagocytic activity of human macrophages in culture

The effect of bacterial exotoxins and endotoxins on phagocytosis was tested on human macrophages in monolayer cultures by determining the rate of zymosan particle ingestion at different toxin concentrations and incubation times. The exotoxins tested were staphylococcal alpha-toxin and diphtheria-toxin. The endotoxins used were lipopolysaccharides from Salmonella typhi, Salmonella typhimurium, Shigella flexneri and Serratia marcescens. Phagocytosis was significantly impaired after prolonged incubation with diphtheria toxin whereas alpha-toxin was ineffective. Endotoxin-treated macrophages showed a wide range of phagocytic activity. Enhancement of phagocytosis was observed with a low concentration of endotoxin (1 microgram/ml) from S. typhi, S. typhimurium and S. flexneri. Higher concentrations (2.5 and 5 micrograms/ml) depressed phagocytosis to varying extents, except for S. typhi lipopolysaccharide, which did not induce a significant decrease in phagocytosis in comparison to the controls.