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The ultrastructure of actinomycetoma grains caused by Streptomyces somaliensis
Abstract:
This study compares the in vitro ultrastructure of Streptomyces somaliensis with the grain formation seen in vivo. Cultured forms were cocco-bacillary with thick cell walls and septa. Individual cells stained with PAS.TCH and Alcian blue. Grains were largely composed of an electron-dense fibrillar matrix surrounding clear areas, some of which contained organisms. The ultrastructural appearances of the latter were not significantly different from those seen in vitro although the cell wall was less well defined and did not stain with Alcian blue, and there were more intracellular lipid droplets. Host cells surrounding the mass were incorporated into the structure of the grain, a process associated with cell death. The grains of S. somaliensis appear to be derived from both host and actinomycete elements. Compared to other mycetoma agents the mechanism of grain formation by this organism is distinctive.
Insights
This study reveals Streptomyces somaliensis grain formation involves both host and bacterial elements, differing from other mycetoma agents. The in vitro and in vivo ultrastructure comparison highlights unique characteristics of this actinomycete.
Area of Science:
- Medical Mycology
- Microbiology
- Pathology
Background:
- Mycetoma is a chronic fungal or bacterial infection.
- Streptomyces somaliensis is a causative agent of mycetoma.
- The mechanism of grain formation in S. somaliensis mycetoma is not fully understood.
Purpose of the Study:
- To compare the in vitro ultrastructure of Streptomyces somaliensis with the in vivo grain formation.
- To elucidate the cellular and extracellular components involved in S. somaliensis grain development.
Main Methods:
- In vitro culture of Streptomyces somaliensis.
- Transmission electron microscopy (TEM) for ultrastructural analysis.
- Histochemical staining (PAS, Alcian blue) of cultured cells.
- Analysis of mycetoma grains from infected hosts.
Main Results:
- In vitro cultured S. somaliensis showed cocco-bacillary forms with thick cell walls.
- In vivo grains contained an electron-dense fibrillar matrix with embedded organisms.
- Host cells were incorporated into grain structure, associated with cell death.
- In vivo organisms had less defined cell walls and more intracellular lipid droplets compared to in vitro forms.
Conclusions:
- Streptomyces somaliensis grain formation is a distinctive process involving both host and actinomycete-derived materials.
- The ultrastructure of S. somaliensis in grains differs subtly from in vitro cultured forms.
- Understanding this unique mechanism may inform mycetoma treatment strategies.