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A study of virulence factors with induced mutants of Staphylococcus aureus
Abstract:
The contribution of a number of extracellular products of Staphylococcus aureus to the virulence of the organism for mice was studied by comparing a wild-type strain with various mutants derived from it in three virulence tests: (1) subcutaneous and (2) intravenous challenge in normal mice, and (3) subcutaneous challenge in mice after total body X-irradiation. Mutants with lower production or non-production of coagulase, staphylokinase and leucocidin were just as virulent for mice as the wild type in all three tests. Unlike the wild type, mutants with low production or nonproduction of alpha-lysin never gave necrosis after subcutaneous injection in normal mice. One mutant with loss of delta-lysin and unaltered alpha-lysin production gave necrosis only when injected in high doses. Dermonecrosis seems to be caused by a combination of alpha- and delta-lysin. Intravenous injection of each of the two types of mutant in normal mice gave a lower mortality rate than that obtained with the wild type. Mutants with deficient alpha-lysin production, but not delta-lysin-deficient mutants, multiplied more slowly in the kidneys than the wild type under these conditions. alpha-Lysin appears to have a growth-enhancing effect for the organism in vivo, but delta-lysin does not. Differences in virulence between the wild type and mutants could not be demonstrated in irradiated mice.
Insights
Staphylococcus aureus virulence factors alpha-lysin and delta-lysin are key to causing skin necrosis and mortality in mice. Alpha-lysin also aids bacterial growth within the host.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Immunology
Background:
- Staphylococcus aureus is a significant human pathogen.
- Extracellular products contribute to bacterial virulence.
- Understanding specific virulence factors is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the role of specific Staphylococcus aureus extracellular products in mouse virulence.
- To determine the contribution of coagulase, staphylokinase, leucocidin, alpha-lysin, and delta-lysin to pathogenesis.
Main Methods:
- Comparison of wild-type Staphylococcus aureus with various mutant strains.
- Virulence testing in mice via subcutaneous and intravenous challenge.
- Assessment of dermonecrosis and bacterial multiplication in kidneys.
- Evaluation in both normal and X-irradiated mice.
Main Results:
- Coagulase, staphylokinase, and leucocidin mutants showed similar virulence to wild-type.
- Alpha-lysin and delta-lysin mutants exhibited reduced dermonecrosis and mortality.
- Alpha-lysin-deficient mutants showed impaired kidney colonization, suggesting a growth-enhancing role.
- Delta-lysin did not appear to enhance bacterial growth in vivo.
- Virulence differences were not evident in irradiated mice.
Conclusions:
- Alpha-lysin and delta-lysin are critical virulence factors for Staphylococcus aureus, particularly in causing dermonecrosis and systemic infection.
- Alpha-lysin plays a role in promoting bacterial proliferation within the host.
- The contribution of other tested extracellular products to mouse virulence is limited.