Related Experiment Videos
Production of "virulence factors" by "epidemic" methicillin-resistant Staphylococcus aureus in vitro
J Z Jordens1, G J Duckworth, R J Williams
1Department of Medical Microbiology, London Hospital Medical College.
Abstract:
The production of virulence factors was determined quantitatively for clinical isolates of methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains of Staphylococcus aureus from The London Hospital. The examined factors were: production of enterotoxins A, B, C and D, determined by ELISA; quantitation and differentiation of the membrane-damaging alpha, beta, gamma and delta haemolysins; and coagulase production determined by a chromogenic assay. Enterotoxin A was produced by MRSA but not by MSSA. All the strains produced haemolysins alpha, gamma and delta at similar levels, but MRSA produced significantly more coagulase than MSSA. MRSA and MSSA were compared in a phagocytosis assay but there was no difference between the phagocytosis of MRSA and MSSA by human polymorphonuclear leucocytes. These findings indicate that MRSA from The London Hospital is at least as well equipped to cause disease as other isolates of S. aureus, and probably better equipped than most hospital isolates of MSSA.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) produced enterotoxin A and more coagulase than methicillin-sensitive strains (MSSA). Both strains showed similar levels of other virulence factors, with no difference in phagocytosis. MRSA appears well-equipped for disease.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacteriology
Background:
- Staphylococcus aureus is a common pathogen, with methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains posing significant clinical challenges.
- Understanding the virulence factors of MRSA and MSSA is crucial for developing effective treatment strategies.
Purpose of the Study:
- To quantitatively compare the production of key virulence factors between clinical isolates of MRSA and MSSA.
- To assess the role of specific toxins and enzymes in the pathogenicity of these strains.
Main Methods:
- Enzyme-linked immunosorbent assay (ELISA) was used to determine enterotoxin production (A, B, C, D).
- Quantitation and differentiation of alpha, beta, gamma, and delta haemolysins were performed.
- Coagulase production was measured using a chromogenic assay.
- Phagocytosis assays with human polymorphonuclear leucocytes compared MRSA and MSSA uptake.
Main Results:
- Enterotoxin A was exclusively produced by MRSA isolates.
- MRSA isolates produced significantly higher levels of coagulase compared to MSSA.
- All strains produced similar levels of alpha, gamma, and delta haemolysins; beta haemolysin levels were not specified as different.
- No significant difference was observed in the phagocytosis of MRSA versus MSSA by human immune cells.
Conclusions:
- MRSA strains from The London Hospital exhibit enhanced virulence factor production, notably enterotoxin A and coagulase.
- These findings suggest MRSA is at least as capable of causing disease as other Staphylococcus aureus isolates, and potentially more so than MSSA.
- The comparable phagocytosis rates indicate that virulence factor differences, not immune evasion, may be key to MRSA's pathogenicity in this context.