Nutritionally variant streptococci develop ultrastructural abnormalities during experimental endocarditis

Area of Science:

• Microbiology
• Pathology
• Infectious Diseases

Background:

• Nutritionally variant streptococci (NVS) cause a significant proportion of endocarditis cases, often presenting as negative blood cultures.
• The resistance of NVS to antibiotics in infected tissues is a clinical concern.
• Understanding NVS behavior within cardiac vegetations is crucial for developing effective treatments.

Purpose of the Study:

• To investigate the ultrastructural changes of NVS within cardiac vegetations during experimental endocarditis.
• To observe the dynamic alterations of NVS at different stages of the disease.
• To assess the impact of antibiotic treatment on NVS morphology in vivo.

Main Methods:

• An experimental rabbit model of endocarditis was established.
• Scanning and transmission electron microscopy were employed to examine NVS ultrastructure.
• Ruthenium red staining was used to detect exopolysaccharide.
• Bacterial morphology was compared between untreated and antibiotic-treated groups.

Main Results:

• In early endocarditis (day 7), NVS showed typical streptococcal morphology.
• By day 11 and 18, NVS formed large clusters with abnormal ultrastructural features, indicative of unbalanced growth.
• Extensive exopolysaccharide surrounding NVS clusters was observed in later stages.
• Antibiotic treatment with penicillin or vancomycin prevented these bacterial alterations.

Conclusions:

• NVS undergo significant ultrastructural changes within cardiac vegetations during endocarditis.
• These changes, including exopolysaccharide production, may be linked to nutrient limitation in bacterial clusters.
• Antibiotic intervention can prevent these pathological bacterial adaptations.
• These findings suggest a potential mechanism for NVS pathogenicity and antibiotic resistance in endocarditis.