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Electron microscopic studies on streptococci. I. M antigen
Abstract:
The presence of M antigens on group A streptococci is associated with hairlike fimbriae that cover the surface of the streptococcal cell wall and are demonstrable by electron microscopy. These fimbriae also may be associated with R antigen. Like M protein, the surface fimbriae are destroyed by trypsin treatment and reappear when "trypsinized" streptococci are reincubated in fresh, trypsin-free broth. Ferritin-conjugated, type-specific antibodies localize on homologous M+ cells in a pattern suggestive of several M antigenic sites along the length of individual surface fimbria. The M-associated fimbriae remain on the residual cell wall after removal of the bulk of group-specific polysaccharide through nitrous acid extraction. This suggests attachment of the fimbriae to the mucopeptide and minor polysaccharide components remaining in the nitrous acid-extracted wall. The pattern of localization of ferritin-conjugated antibodies on homologous streptococci before and after trypsin exposure and upon reincubation of the trypsinized cells in fresh medium suggests the following hypothesis: M antigen is secreted by the cell, is partially excreted through the otherwise intact cell wall, and is bound by the wall so that M protein occupies a peripheral, exposed position on the surfaces of the streptococcal cell wall.
Insights
Group A streptococci possess M antigens on surface fimbriae, which are trypsin-sensitive and reappear upon reincubation. These M-associated fimbriae are attached to the cell wall, suggesting M antigen
Area of Science:
- Microbiology
- Bacteriology
- Immunology
Background:
- Group A streptococci (GAS) possess M antigens, crucial virulence factors.
- M antigens are associated with surface fimbriae, hair-like appendages on the bacterial cell wall.
- The precise location and structure of M antigens on GAS remain under investigation.
Purpose of the Study:
- To investigate the association between M antigens and surface fimbriae in group A streptococci.
- To elucidate the structural localization and secretion mechanism of M antigens on the streptococcal cell surface.
Main Methods:
- Electron microscopy to visualize fimbriae.
- Trypsin treatment to assess antigen sensitivity and regeneration.
- Nitrous acid extraction to remove group-specific polysaccharides.
- Immunoelectron microscopy using ferritin-conjugated antibodies to localize M antigens.
Main Results:
- M antigens are located on hairlike fimbriae covering the streptococcal cell surface.
- These fimbriae are trypsin-sensitive and regenerate upon reincubation in fresh broth.
- M-associated fimbriae remain attached to the cell wall after polysaccharide removal, suggesting linkage to mucopeptide components.
- Ferritin-conjugated antibodies localize along the length of individual fimbriae.
Conclusions:
- M antigen is secreted by the bacterium and partially excreted through the cell wall.
- M protein is bound to the cell wall, occupying a peripheral and exposed position on the fimbriae.
- This surface localization of M antigen likely plays a role in streptococcal virulence and host interaction.