49. Group B, C, D & G streptococci. Streptococcus viridians group. Genus Enterococcus
Covers the main features, virulence factors, clinical disease, diagnosis and treatment of Streptococcus agalactiae, then group C and G streptococci, group D non-enterococcal streptococci of the S. bovis group, the viridans streptococci with their key species and dental and endocarditis links, and finally the genus Enterococcus. Tables summarise virulence factors, disease patterns and treatment by severity, including vancomycin-resistant enterococci.
Topic 49 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 6 sections, about 353 words (4 min of reading), with 14 flashcards.
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Group B, C, D & G Streptococci. Streptococcus Viridans. Genus Eneterococcus.
Group B Streptococci – Streptococcus agalactiae
Group C & G Streptococci
Group D Streptococci (non-enterococcal) – Streptococcus bovis group
Streptococcus viridans group
Genus Enterococcus (Group D Enterococci)
Group B Streptococci – Streptococcus agalactiae
General Features:
Gram-positive cocci in chains.
β-hemolytic on blood agar.
Catalase-negative, Bacitracin-resistant.
CAMP test positive – enhances hemolysis by S. aureus → “arrowhead” pattern.
Part of the normal flora of the vagina, GI, and URT.
Virulence Factors:
Epidemiology:
Causes neonatal infections, postpartum infections, and elderly infections.
Transmission: during delivery or from maternal genital tract.
Clinical Disease:
Diagnosis:
Culture from blood/CSF.
CAMP test positive.
Gram stain: chains of G+ cocci.
Antigen testing is not sensitive enough.
Treatment:
Penicillin G – first-line.
Severe: combine with aminoglycosides (e.g., gentamicin).
Vancomycin if allergic to penicillin.
Prevention: screen pregnant women at 35–37 weeks + prophylaxis if positive.
Group C & G Streptococci
β-hemolytic, catalase-negative.
Normal flora of throat, skin, GI.
Cause pharyngitis, skin infections, bacteremia, and rarely rheumatic fever.
Not part of regular screening unless recurrent infections occur.
Diagnosed by blood agar + Lancefield grouping.
Group D Streptococci (non-enterococcal) – Streptococcus bovis group
Gram-positive cocci, α- or γ-hemolytic, non-enterococcal.
Catalase-negative, bile esculin positive.
Found in GI tract of humans.
Clinical importance:
Strong association with colorectal cancer.
Also causes endocarditis, bacteremia.
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