Related Experiment Videos
Susceptibility of chicken embryos to group A streptococci: correlation with fibrinogen binding
K H Schmidt1, J Wiesner, D Gerlach
1University of Jena, Institute of Experimental Microbiology, FRG.
Abstract:
One problem in investigating group A streptococcal infections and virulence is the lack of appropriate in vivo models. In this study we introduce the chicken embryo model for determining virulence of Streptococcus pyogenes. We found that M protein positive strains, if administered intravenously, were highly virulent for 12-day-old chicken embryos. The LD50 of the strains tested could be correlated directly with the amount of cell wall exposed M protein, which has been determined by the capacity of streptococci to bind fibrinogen and by the ability of streptococci to survive in fresh normal human blood. The number of colony forming units (cfu) of M+ strains necessary to kill 50% of embryonated eggs was significantly lower (< 10(2) cfu) than for M-variants (> 10(4) cfu). Albumin and/or IgG binding streptococcal cells, which can also take place in proteins of the M protein family which do not bind to fibrinogen, did not show that clear correlation to the virulence in chicken embryos that did fibrinogen binding. Application of anti-streptococcal M protein antisera from chicken and rabbit reduced the lethality of the chicken embryos. In contrast, no correlation was found between lethality of chicken embryos and the in vitro production of erythrogenic toxins by the administered strains. Thus the results indicate that the presence of M-protein with its fibrinogen binding activity on the streptococcal cell surface is necessary for virulence of group A streptococci in the chicken embryo model.
Insights
This study introduces a chicken embryo model to assess Streptococcus pyogenes virulence. M protein-positive strains showed high virulence, directly correlating with fibrinogen binding, highlighting M protein
Area of Science:
- Microbiology
- Infectious Diseases
- Animal Models
Background:
- Investigating Group A Streptococcus (GAS) virulence is hindered by a lack of suitable in vivo models.
- Streptococcus pyogenes virulence factors require effective in vivo assessment.
Purpose of the Study:
- To introduce and validate a chicken embryo model for determining Streptococcus pyogenes virulence.
- To investigate the role of M protein in GAS virulence using the developed model.
Main Methods:
- Intravenous administration of Streptococcus pyogenes strains to 12-day-old chicken embryos.
- Quantification of M protein expression via fibrinogen binding and human blood survival assays.
- Determination of lethal dose 50 (LD50) and correlation with M protein presence and function.
Main Results:
- M protein-positive (M+) S. pyogenes strains demonstrated high virulence in chicken embryos (LD50 < 10^2 cfu).
- Virulence correlated directly with cell wall-exposed M protein, measured by fibrinogen binding and blood survival.
- Anti-streptococcal M protein antisera reduced embryo lethality; erythrogenic toxin production did not correlate with virulence.
Conclusions:
- The chicken embryo model is effective for evaluating S. pyogenes virulence.
- Fibrinogen-binding M protein on the streptococcal cell surface is essential for virulence in this model.
- This model provides a valuable tool for understanding GAS pathogenesis and M protein function.