Human endocarditis due to nutritionally variant streptococci: streptococcus adjacens and Streptococcus defectivus

Area of Science:

• Microbiology
• Infectious Diseases
• Cardiology

Background:

• Streptococcus adjacens and S. defectivus are recently identified viridans streptococci species.
• Previously classified as nutritionally variant streptococci, they exhibit unique growth requirements, often needing helper bacteria or enriched media.

Purpose of the Study:

• To characterize Streptococcus adjacens and S. defectivus.
• To investigate their role in endocarditis and treatment outcomes.
• To evaluate therapeutic strategies for endocarditis caused by these bacteria.

Main Methods:

• Morphological and growth studies using semi-chemically defined media.
• Analysis of clinical data on endocarditis cases.
• Experimental models of endocarditis to assess antimicrobial efficacy.

Main Results:

• These species are primarily found in the oral, intestinal, and genito-urinary tracts.
• They are implicated in a significant percentage of blood-culture-negative endocarditis cases.
• Endocarditis caused by these bacteria shows higher failure, relapse, and mortality rates compared to other viridans streptococci.

Conclusions:

• The slow growth and exopolysaccharide production by S. adjacens and S. defectivus contribute to treatment challenges in endocarditis.
• Extended antimicrobial therapy may be necessary for successful treatment.
• Vancomycin is effective as an alternative therapy when standard treatments fail or are contraindicated.