Streptococcus dysgalactiae
- Bacterium
Gram-positive
Thick peptidoglycan wall: stains purple.- For completeness
A cousin of the strep throat bacterium that causes sore throat, cellulitis and bloodstream infection, mostly in older or sick adults.
Also called: group C and G streptococci, S. dysgalactiae subsp. equisimilis (SDSE)
Quick facts
- Type
- Bacterium · Streptococci and enterococci
- Gram / shape
- Gram-positive · Cocci in chains
- Spread
- Carried on skin and in the throat
- Causes
- Cellulitis and erysipelas · Bacteraemia
- Treatment
- Treated like group A
At a glance
- Gram
- Gram-positive
- Shape
- Cocci in chains
- Oxygen
- Facultative anaerobe
- Family
- Streptococcaceae
- Size
- Large beta-haemolytic colonies like group A
Morphology
- Gram-positive cocci in chains; catalase-negative
- Beta-haemolytic large colonies that look like Streptococcus pyogenes
- Carries Lancefield group C or G antigen (rarely A or L)
Transmission
- Carried on skin and in the throat; enters through skin breaks
- Respiratory droplets for pharyngitis; foodborne pharyngitis outbreaks have occurred
- Animal-linked group C species (S. equi subsp. zooepidemicus) come from horses and unpasteurised milk
Reservoir: Human skin, throat, gut and genital tract; animals for some group C species
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- M protein that resists phagocytosis, as in group A
- Streptolysins and streptokinase
- Some lineages are especially invasive
Diseases it causes
- Pharyngitis indistinguishable from group A strep throat Streptococcal pharyngitis →
- Cellulitis and erysipelas, often recurrent in legs with lymphoedema or venous disease Cellulitis of the leg →
- Bacteraemia, usually from a skin source Sepsis and septic shock →
- Septic arthritis, including prosthetic joints Septic Arthritis of the Knee →
- Infective endocarditis Infective endocarditis →
- Necrotizing fasciitis and streptococcal toxic shock syndrome Necrotizing soft tissue infection (necrotizing fasciitis, gas gangrene) →
Clinical picture
- Typical patient: older adult with diabetes, cancer, skin breakdown or chronic oedema
- Recurrent leg cellulitis
- Raw-milk outbreaks of S. zooepidemicus have caused post-streptococcal glomerulonephritis
Diagnosis
- Blood, tissue or joint culture; beta-haemolysis and Lancefield grouping
- Throat culture identifies it; rapid group A antigen tests usually do not detect it
- MALDI-TOF mass spectrometry to species
Treatment
Treated like group A: penicillin is the drug of choice, with cephalosporins as alternatives and clindamycin added in toxin-mediated severe disease. Macrolide, clindamycin and tetracycline resistance varies by region, so test isolates; surgery for necrotizing infection.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Skin care and treatment of foot fungal infection and leg oedema to prevent recurrent cellulitis
- Pasteurisation of milk
- No vaccine
Test yourself
Think of the answer, then tap the question to see it.
Which species is the main human pathogen among group C and G streptococci?
Streptococcus dysgalactiae subsp. equisimilis.
Which virulence factors does S. dysgalactiae share with group A streptococcus?
M protein, streptolysins and streptokinase.
Which antibiotic is the drug of choice for group C and G streptococcal infection?
Penicillin, as for group A.
Why can a rapid strep test be negative in group C or G pharyngitis?
Rapid tests detect the group A antigen, which these strains usually do not carry.
Connections
← Back to the group: Streptococci and enterococci
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Infections Caused by Group C and G Streptococcus (Streptococcus dysgalactiae subsp. equisimilis and Others): Epidemiological and Clinical Aspects (Microbiology Spectrum (ASM), 2019); Streptococcal Infections - Infectious Disease - MSD Manual Professional Edition (MSD Manual Professional Edition, 2025).
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Representative model, for educational purposes only.