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Early events after intra-abdominal infection with Bacteroides fragilis and Escherichia coli
W R Verweij1, F Namavar, W F Schouten
1Department of Medical Microbiology, School of Medicine, Vrije Universiteit, Amsterdam, The Netherlands.
Abstract:
Growth of Bacteroides fragilis and Escherichia coli was monitored during early stages of single (mono-) and mixed intra-abdominal infection in a rat fibrin clot model. When B. fragilis and E. coli were together involved in the infection, B. fragilis numbers increased about 6 h after an initial decline. This increase was not found with B. fragilis mono-infections. The numbers of E. coli increased rapidly in both mono- and mixed infections and stayed high for several days, but only mixed infection resulted in abscesses that persisted for more than 7 days. Macrophages, the main component of the peritoneal cellular defence mechanism, were outnumbered by polymorphonuclear leucocytes during the first 6 h of infection. Further characterisation of the macrophage population by means of monoclonal antibodies showed a shift from resident to exudate macrophages as the result of influx of the latter.
Insights
In mixed infections, Bacteroides fragilis numbers increased after an initial decline, unlike in single infections. Mixed infections with Escherichia coli also led to persistent abscesses in rats.
Area of Science:
- Microbiology and Immunology
- Infectious Diseases
- Animal Models of Infection
Background:
- Intra-abdominal infections often involve polymicrobial communities.
- Understanding the dynamics of bacterial growth and host response is crucial for effective treatment.
- The role of specific bacterial interactions in infection pathogenesis remains incompletely understood.
Purpose of the Study:
- To investigate the early growth dynamics of Bacteroides fragilis and Escherichia coli in mono- and mixed intra-abdominal infections.
- To characterize the host's cellular immune response during these infections.
- To determine the impact of bacterial interactions on abscess formation and persistence.
Main Methods:
- A rat fibrin clot model was used to establish intra-abdominal infections.
- Bacterial growth of B. fragilis and E. coli was monitored in both mono- and mixed infections.
- Peritoneal cellular defense mechanisms, including macrophage populations, were analyzed using monoclonal antibodies.
Main Results:
- In mixed infections, B. fragilis exhibited an increase in numbers approximately 6 hours after an initial decrease, a phenomenon not observed in mono-infections.
- E. coli demonstrated rapid and sustained growth in both mono- and mixed infections.
- Persistent abscesses (>7 days) were only observed in rats with mixed infections.
Conclusions:
- Bacteroides fragilis and Escherichia coli exhibit synergistic interactions during intra-abdominal infection, influencing bacterial dynamics and host response.
- The observed increase in B. fragilis during mixed infection suggests a supportive role of E. coli or a compromised host defense.
- Mixed infections lead to more severe pathology, characterized by persistent abscess formation, highlighting the importance of polymicrobial interactions in virulence.