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Experimental staphylococcal endocarditis and aortitis. Morphology of the initial colonization
Abstract:
The initial colonization, by Staphylococcus aureus, of the catheter damaged aortic valve and aorta of the rabbit, was examined by light and electron microscopy at 15 min, 3 h and 24 h post inoculation (PI). At 15 min PI, the majority of bacteria (80%) were located on the lateral surfaces of the thrombic vegetations while 20% were attached directly to the connective tissue of the aortic valve and aorta in areas where the endothelial lining was disrupted. By 3 h the bacteria on the thrombic vegetations were covered by fibrin. At this time, the bacteria both within the vegetations and on the surface of the vasculature were undergoing multiplication to form small groups. The precipitation of thrombus around the bacteria attached to the surface of the aorta to form microscopic infected vegetations had occurred by 24 h PI. The colonizing bacteria did not elicit any phagocytic response. The colonization of the cardiovasculature by Staph. aureus did not necessarily require pre-existing vegetations.
Insights
Staphylococcus aureus rapidly colonizes damaged rabbit aortas, forming infected vegetations within 24 hours. This bacterial invasion occurs even without pre-existing vegetations and does not trigger a phagocytic response.
Area of Science:
- Cardiovascular Science
- Microbiology
- Pathology
Background:
- Catheter-induced damage to the aortic valve and aorta can create sites for bacterial colonization.
- Staphylococcus aureus is a common pathogen implicated in cardiovascular infections.
Purpose of the Study:
- To investigate the early stages of Staphylococcus aureus colonization on damaged aortic valves and aortas in a rabbit model.
- To understand the temporal dynamics of bacterial attachment, multiplication, and vegetation formation.
Main Methods:
- Light and electron microscopy were used to examine infected tissues at 15 minutes, 3 hours, and 24 hours post-inoculation.
- A rabbit model with catheter-induced damage to the aortic valve and aorta was utilized.
Main Results:
- Initially, Staphylococcus aureus primarily attached to thrombotic vegetations (80%) and disrupted endothelial surfaces (20%).
- Within 3 hours, bacteria on vegetations were fibrin-covered and began multiplying.
- By 24 hours, microscopic infected vegetations formed on the aorta, and no phagocytic response was observed.
- Colonization occurred even without pre-existing vegetations.
Conclusions:
- Staphylococcus aureus rapidly colonizes damaged cardiovascular tissues.
- The formation of infected vegetations is a swift process involving thrombus precipitation.
- The absence of a phagocytic response suggests immune evasion mechanisms may be involved.