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Updated: Aug 17, 2026
Murine Oropharyngeal Aspiration Model of Ventilator-associated and Hospital-acquired Bacterial Pneumonia
Published on: June 28, 2018
Dynamics of intrapulmonary bacterial growth in a murine model of repeated microaspiration
Itzhak Ben-David1, Sarah E Price, David M Bortz
1Department of Emergency Medicine, University of Michigan, Ann Arbor, Michigan, USA.
Abstract:
To study the change in intrapulmonary bacterial growth rate over time during Gram-negative pneumonia, a two-hit model of recurrent bacterial aspiration was developed in mice. A mutant of Klebsiella pneumoniae was isolated that could be distinguished from the wild type when cultured on appropriate media. These strains were intranasally administered, 4 h apart, to mice whose lungs were quantitatively cultured 24 h later. The relative burden of each aspirated inoculum was determined, and, using the administered dose and the number of bacteria from each inoculum present at the end of the experiment, first-order growth constants for each inoculum were calculated. Results indicate that after an initial aspiration of this organism, subsequently aspirated bacteria proliferate more slowly. When two aspirations occurred 4 h apart, the bacteria aspirated first represented 96% of total lung burden at 24 h. The growth constant of the second inoculum was related to the magnitude of the first inoculum in an inverse, nonlinear fashion. When parallel experiments were performed in complement C3-deficient mice, no suppression of the second inoculum was noted, suggesting that early upregulation of antibacterial activity in the lung is a C3-mediated event.
Insights
Recurrent bacterial pneumonia in mice shows that a second Klebsiella pneumoniae aspiration leads to slower bacterial growth. This immune response in the lungs is mediated by complement C3.
Area of Science:
- Immunology
- Microbiology
- Pulmonology
Background:
- Gram-negative pneumonia can involve recurrent bacterial challenges.
- Understanding bacterial growth dynamics during pneumonia is crucial for treatment.
- The role of the innate immune system in controlling secondary infections is not fully elucidated.
Purpose of the Study:
- To investigate the intrapulmonary bacterial growth rate changes over time during Gram-negative pneumonia.
- To model recurrent bacterial aspiration in mice to study the host-pathogen interaction.
- To determine the role of complement C3 in the immune response to secondary bacterial challenge.
Main Methods:
- Developed a two-hit model using intranasal administration of distinguishable Klebsiella pneumoniae strains in mice.
- Quantitatively cultured mouse lungs 24 hours post-aspiration to determine bacterial burden.
- Calculated first-order growth constants for each bacterial inoculum and performed experiments in complement C3-deficient mice.
Main Results:
- Subsequent bacterial aspirations resulted in significantly slower proliferation compared to the initial inoculum.
- The first inoculum constituted 96% of the total lung burden when aspirations were 4 hours apart.
- The growth rate of the second inoculum was inversely and non-linearly related to the magnitude of the first inoculum.
Conclusions:
- Early intrapulmonary bacterial growth is suppressed following a primary Gram-negative pneumonia insult.
- This suppression is dependent on complement C3, indicating its critical role in early antibacterial defense.
- The findings suggest a C3-mediated upregulation of antibacterial activity in the lung following initial infection.
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