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Probable L-forms of Nocardia asteroides induced in cultured mouse peritoneal macrophages
Abstract:
Mouse peritoneal macrophages were infected with varying numbers of Nocardia asteroides 10905, and the fate of the ingested organisms was determined by viable plate count (VPC), light microscopy (LM), immunofluorescent microscopy (IM), and electron microscopy (EM). The results obtained with these methods differed. VPC indicated that intracellular Nocardia decreased in numbers during the first 12 days, followed by significant increases after 16 days. LM suggested that N. asteroides 10905 was slowly degraded by macrophages with no subsequent increases observed. In contrast, IM demonstrated large numbers of intracellular Nocardia throughout the experiment. EM studies of infected macrophages failed to demonstrate intact bacteria after 8 days; however, wall-less and spheroplast-like organisms were seen. These results suggested that N. asteroides 10905 was present within the macrophages in an altered form. By using hypertonic culture medium, we were able to isolate, from infected macrophages, organisms which exhibited many of the properties of bacterial L-forms. IM demonstrated these variants to be of nocardial origin. These altered forms also reverted to typical nocardial cells either spontaneously or upon transfer into broth. These findings indicate that N. asteroides 10905 is capable of existing within macrophages in an altered state. Further investigation is in progress to determine whether these altered forms represent L-forms or transitional-phase variants.
Insights
Nocardia asteroides 10905 can survive inside mouse macrophages by transforming into an altered, wall-less state, resembling bacterial L-forms. These variants can revert to typical cells, indicating a unique survival mechanism within host immune cells.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Macrophages are key immune cells involved in phagocytosing and eliminating microbial pathogens.
- Nocardia asteroides is an opportunistic bacterial pathogen known to cause infections in immunocompromised individuals.
Purpose of the Study:
- To investigate the intracellular fate of Nocardia asteroides 10905 within mouse peritoneal macrophages.
- To determine if Nocardia asteroides can alter its morphology or state within macrophages.
Main Methods:
- Infection of macrophages with Nocardia asteroides 10905.
- Utilizing viable plate count (VPC), light microscopy (LM), immunofluorescent microscopy (IM), and electron microscopy (EM) to assess bacterial survival and morphology.
- Isolation and characterization of intracellular bacterial variants using hypertonic culture medium.
Main Results:
- Discrepant results observed across different methodologies (VPC, LM, IM, EM) regarding Nocardia survival and morphology.
- Electron microscopy revealed the presence of wall-less and spheroplast-like organisms, suggesting an altered bacterial state.
- Isolation of bacterial variants from macrophages exhibiting properties of bacterial L-forms, capable of reverting to typical nocardial cells.
Conclusions:
- Nocardia asteroides 10905 can exist within macrophages in an altered, potentially wall-less or L-form state.
- This intracellular transformation represents a survival strategy for Nocardia asteroides within the host immune environment.
- Further research is needed to confirm if these altered forms are true L-forms or transitional variants.