Related Experiment Video
Updated: Aug 29, 2026
Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes
Published on: August 9, 2011
Electron microscopic observations on the interaction of Listeria monocytogenes and peritoneal macrophages of normal
Abstract:
Acid phosphatase histochemistry was performed to study ultrastructurally the intracellular survival and digestion of Listeria monocytogenes in normal mouse peritoneal macrophages. Acid phosphatase activity proved to be a useful marker for digestive processes of the macrophages, as this activity could be seen in the cytoplasm of killed listeria before disintegration, but not in viable listeria. Almost all killed listeria and the majority of the viable listeria were found in phagosomes of the loosely fitting type. The fusion of lysosomes and phagosomes containing killed bacteria was completed very quickly; the fusion involving phagosomes containing viable listeria was delayed. This delay was abolished by opsonization of bacteria. Disintegration of killed listeria in macrophages could be seen. No such effects were observed when viable listeria were used. Increased numbers of listeria within the phagosomes upon longer incubation suggest multiplication within macrophages.
Insights
This study shows that acid phosphatase activity marks the digestion of killed Listeria monocytogenes in mouse macrophages. Viable Listeria monocytogenes may multiply within macrophages, as indicated by increased numbers.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Listeria monocytogenes is a facultative intracellular bacterium.
- Macrophages play a crucial role in the innate immune response against bacterial infections.
- Understanding the intracellular fate of Listeria monocytogenes within macrophages is key to developing effective treatments.
Purpose of the Study:
- To investigate the intracellular survival and digestion of Listeria monocytogenes in mouse peritoneal macrophages.
- To utilize acid phosphatase activity as a marker for macrophage digestive processes.
- To examine the role of phagosome-lysosome fusion in the clearance of Listeria monocytogenes.
Main Methods:
- Acid phosphatase histochemistry was employed to study the ultrastructural changes.
- Normal mouse peritoneal macrophages were infected with Listeria monocytogenes.
- The localization and activity of acid phosphatase were assessed in relation to bacterial viability and phagosome-lysosome fusion.
Main Results:
- Acid phosphatase activity was observed in killed Listeria monocytogenes, indicating digestion, but not in viable bacteria.
- Most Listeria monocytogenes were found in loosely fitting phagosomes.
- Phagosome-lysosome fusion was rapid for killed bacteria but delayed for viable bacteria, an effect reversed by opsonization.
- Evidence suggests potential multiplication of viable Listeria monocytogenes within macrophages.
Conclusions:
- Acid phosphatase is a reliable marker for the intracellular digestion of Listeria monocytogenes by macrophages.
- Delayed phagosome-lysosome fusion contributes to the survival of viable Listeria monocytogenes within macrophages.
- Opsonization enhances the clearance of Listeria monocytogenes by promoting phagosome-lysosome fusion.
- Listeria monocytogenes may evade macrophage-mediated killing and potentially multiply intracellularly.
