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Updated: Aug 10, 2025

Measuring Phagosome pH by Ratiometric Fluorescence Microscopy
Published on: December 7, 2015
Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH.
Jesus S Distel1, Gisela Di Venanzio1, Joseph J Mackel2
1Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, Missouri, United States of America.
Clinical Acinetobacter baumannii strains, unlike lab strains, persist in lung macrophages by forming specialized vacuoles. This survival mechanism, involving ammonia secretion, is crucial for respiratory infection persistence.
Area of Science:
- Microbiology
- Immunology
- Pathogen Biology
Background:
- Multidrug-resistant Acinetobacter baumannii causes dangerous nosocomial pneumonia.
- Alveolar macrophages are key to fighting respiratory infections.
Approach:
- Compared clinical A. baumannii isolate 398 with lab strain ATCC 19606 in a murine pneumonia model.
- Tracked bacterial interaction with macrophage endocytic and autophagic pathways.
- Analyzed vacuole formation and bacterial survival mechanisms.
Key Points:
- Clinical isolate 398, but not lab strain 19606, forms Acinetobacter-Containing Vacuoles (ACVs) in vivo.
- A. baumannii 398 replicates within ACVs, evading degradation, while 19606 is eliminated via autophagy.
- Isolate 398 neutralizes phagosome acidity by secreting ammonia.
Conclusions:
- A. baumannii's ability to form ACVs and neutralize phagosomal acidity is critical for persistence in the lung.
- This macrophage survival strategy may explain the prevalence of clinical isolates in pneumonia.
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