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Killing of Mycobacterium avium subspecies paratuberculosis within macrophages
John P Bannantine1, Judith R Stabel
1National Animal Disease Center, ARS-USDA, Ames, Iowa, USA. jbannant@nadc.ars.usda.gov
Background:
Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is a facultative intracellular pathogen that resides within host macrophages during infection of ruminant animals. We examined survival of M. paratuberculosis infections within cultured macrophages to better understand the interplay between bacterium and host.
Results:
Serial plating of M. paratuberculosis infected macrophage lysates on Herold's egg yolk medium showed that mycobacterial replication takes place between 0 and 24 hours post-infection. This initial growth phase was followed by a steady decline in viability over the next six days. Antibodies against M. paratuberculosis were affinity purified and used in conjunction with transmission electron microscopy to track the development of intracellular bacilli. Immunogold labeling of infected macrophages with antibody against M. paratuberculosis showed degraded intracellular mycobacteria that were unrecognizable by morphology alone. Conversely, when macrophages were heavily infected with M. paratuberculosis, no degraded forms were observed and macrophages were killed.
Conclusions:
We present a general description of M. paratuberculosis survival within cultured macrophages using transmission electron microscopy and viability counts. The results of this study provides further insight surrounding M. paratuberculosis-macrophage infections and have implications in the pathogenesis of M. paratuberculosis, a pathogen known to persist inside cattle for many years.
Insights
Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) replicates in macrophages initially, then declines. Heavy infection leads to macrophage death, impacting ruminant health.
Area of Science:
- Veterinary Microbiology
- Cellular Immunology
Background:
- Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is a facultative intracellular pathogen.
- It resides within host macrophages during ruminant infections.
Purpose of the Study:
- To examine M. paratuberculosis survival within cultured macrophages.
- To understand the interplay between M. paratuberculosis and host macrophages.
Main Methods:
- Serial plating of infected macrophage lysates to determine bacterial viability.
- Transmission electron microscopy (TEM) with immunogold labeling to track intracellular bacilli.
Main Results:
- M. paratuberculosis replicated between 0 and 24 hours post-infection, followed by a six-day decline in viability.
- TEM revealed degraded intracellular M. paratuberculosis.
- Heavy M. paratuberculosis infection resulted in macrophage death without observed degradation.
Conclusions:
- The study describes M. paratuberculosis survival in macrophages using TEM and viability counts.
- Findings offer insights into M. paratuberculosis pathogenesis and persistence in cattle.