Histopathological Analysis of Acinetobacter baumannii Lung Infection in a Mouse Model
Shigeru Tansho-Nagakawa1, Yoshinori Sato1, Tsuneyuki Ubagai1
1Department of Microbiology and Immunology, Teikyo University School of Medicine, Tokyo, Japan.
Abstract:
Acinetobacter baumannii is the main causative pathogen of nosocomial infections that causes severe infections in the lungs. In this study, we analyzed the histopathological characteristics of lung infection with two strains of A. baumannii (ATCC 19606 and the clinical isolate TK1090) and Pseudomonas aeruginosa PAO-1 in C3H/HeN mice to evaluate the virulence of A. baumannii. Survival was evaluated over 14 days. At 1, 2, 5, or 14 days postinfection, mice of C3H/HeN were sacrificed, and histopathological analysis of lung specimens was also performed. Histopathological changes and accumulation of neutrophils and macrophages in the lungs after infection with A. baumannii and P. aeruginosa were analyzed. Following intratracheal inoculation, the lethality of ATCC 19606- and TK1090-infected mice was lower than that of PAO-1-infected mice. However, when mice were inoculated with a sub-lethal dose of A. baumannii, the lung bacterial burden remained in the mice until 14 days post-infection. Additionally, histopathological analysis revealed that macrophages infiltrated the lung foci of ATCC 19606-, TK1090-, and PAO-1-infected mice. Although neutrophils infiltrated the lung foci of ATCC 19606- and TK1090-infected mice, they poorly infiltrated the lung foci of PAO-1-infected mice. Accumulation of these cells in the lung foci of ATCC 19606- and TK1090-infected mice, but not PAO-1-infected mice, was observed for 14 days post-infection. These results suggest that A. baumannii is not completely eliminated despite the infiltration of immune cells in the lungs and that inflammation lasts for prolonged periods in the lungs. Further studies are required to understand the mechanism of A. baumannii infection, and novel drugs and vaccines should be developed to prevent A. baumannii infection.
Insights
Acinetobacter baumannii causes severe lung infections, persisting in mice for 14 days despite immune cell infiltration. This prolonged inflammation highlights the need for new treatments against this resilient pathogen.
Area of Science:
- Microbiology
- Immunology
- Pathology
Background:
- Acinetobacter baumannii is a primary cause of hospital-acquired infections, particularly severe lung infections.
- Understanding the virulence and host-pathogen interactions of A. baumannii is crucial for developing effective treatments.
Purpose of the Study:
- To compare the virulence of A. baumannii strains (ATCC 19606 and TK1090) with Pseudomonas aeruginosa PAO-1 in a murine lung infection model.
- To analyze the histopathological changes and immune cell responses in the lungs following infection.
Main Methods:
- C3H/HeN mice were intratracheally inoculated with A. baumannii or P. aeruginosa.
- Survival rates were monitored for 14 days.
- Lung tissues were collected at various time points for histopathological analysis, focusing on immune cell infiltration (neutrophils and macrophages).
Main Results:
- A. baumannii strains exhibited lower lethality than P. aeruginosa but established a persistent lung bacterial burden up to 14 days post-infection.
- Both A. baumannii and P. aeruginosa induced macrophage infiltration in lung foci.
- Neutrophil infiltration was observed in A. baumannii-infected lungs but was limited in P. aeruginosa-infected lungs, with prolonged immune cell accumulation in A. baumannii infections.
Conclusions:
- Acinetobacter baumannii infection leads to persistent inflammation in the lungs, even with immune cell presence.
- The pathogen is not fully cleared, indicating a need for further research into infection mechanisms.
- Development of novel drugs and vaccines is essential to combat A. baumannii infections.
