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Cytotoxic effect of hemolytic culture supernatant from Enterococcus faecalis on mouse polymorphonuclear neutrophils
S Miyazaki1, A Ohno, I Kobayashi
1Department of Microbiology, Toho University School of Medicine, Tokyo, Japan.
Abstract:
We reconfirmed that the LD50s of hemolytic Enterococcus faecalis strains were significantly less than those of nonhemolytic E. faecalis strains in normal mice. Hemolysin produced by E. faecalis lysed human, horse, rabbit, and mouse erythrocytes, but not cow and sheep erythrocytes. Sphingomyelin comprises a part of the lipid composition of the erythrocyte membrane of all mammalian species tested. But phosphatidylcholine exists only in human, horse, rabbit, and mouse. These two lipids inhibited lysis of horse erythrocytes by hemolytic E. faecalis. Phosphatidylcholine is probably the binding component on the membrane of erythrocytes for E. faecalis hemolysin. The hemolytic culture supernatant lysed not only erythrocytes but also mouse polymorphonuclear neutrophils (PMNs) and macrophages.
Insights
Hemolytic Enterococcus faecalis strains are more lethal than nonhemolytic strains. Their hemolysin targets specific erythrocyte lipids, like phosphatidylcholine, and also damages immune cells, impacting virulence.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Enterococcus faecalis is an opportunistic pathogen.
- Hemolytic strains of E. faecalis exhibit increased virulence.
- The specific mechanisms of E. faecalis hemolysin activity are not fully understood.
Purpose of the Study:
- To reconfirm the lower LD50 of hemolytic E. faecalis strains.
- To investigate the erythrocyte membrane components involved in hemolysin-mediated lysis.
- To determine the effect of hemolytic E. faecalis supernatant on immune cells.
Main Methods:
- LD50 determination in normal mice.
- Erythrocyte lysis assays using erythrocytes from various species.
- Lipid inhibition assays with sphingomyelin and phosphatidylcholine.
- Cytotoxicity assays with mouse polymorphonuclear neutrophils and macrophages.
Main Results:
- Hemolytic E. faecalis strains had significantly lower LD50s than nonhemolytic strains.
- E. faecalis hemolysin lysed erythrocytes from humans, horses, rabbits, and mice, but not cows or sheep.
- Phosphatidylcholine, present in susceptible erythrocytes, inhibited hemolysin-induced lysis.
- Hemolytic culture supernatant also lysed mouse polymorphonuclear neutrophils and macrophages.
Conclusions:
- Hemolytic E. faecalis exhibits enhanced virulence, correlating with lower LD50 values.
- Phosphatidylcholine is identified as a likely binding component for E. faecalis hemolysin on erythrocyte membranes.
- E. faecalis hemolysin possesses cytotoxic effects not only on erythrocytes but also on key immune cells, suggesting a broader role in pathogenesis.