Streptococcus dysgalactiae (grupos C e G)
Gram-positive cocci in chains
Identification & Growth
Identification
- Beta-hemolytic, catalase-negative
- Lancefield latex agglutination positive for group C or G
- Large colonies (> 0.5 mm), distinct from Streptococcus anginosus group
Growth Conditions
- Blood agar, 35–37 °C, 5% CO2, 18–24 h; wide zones of beta-hemolysis
Clinical Significance
- Cellulitis, erysipelas, soft-tissue infection in diabetic patients
- Bacteremia, septic arthritis and pharyngitis in adults
Intrinsic Resistance
- Never report susceptibility to aminoglycosides alone
- No confirmed penicillin resistance has been described — an R result requires repeat testing
Bench Alerts
- Penicillin remains the drug of choice; test clindamycin with a D-test
- Differentiate from the anginosus group (small colonies, caramel-like odour)
Clinical Notes
Clinical presentations
- Causes pharyngitis, cellulitis, erysipelas, and soft tissue infections, with clinical presentation similar to Streptococcus pyogenes.
- Can cause bacteremia, infective endocarditis, and septic arthritis, especially in elderly patients with comorbidities.
- Cases of necrotizing fasciitis and streptococcal toxic shock syndrome have been described, similar to those caused by group A.
Specimens and collection
- Oropharyngeal swab is indicated in pharyngitis, though less standardized than for Streptococcus pyogenes.
- Blood cultures should be collected when bacteremia or endocarditis is suspected, with attention to a primary cutaneous focus.
- Deep tissue or joint fluid culture is indicated when invasive soft tissue or joint infection is suspected.
Epidemiology and at-risk populations
- Elderly adults with diabetes, peripheral vascular disease, or lymphedema are at higher risk of recurrent skin and soft tissue infection.
- Incidence of invasive disease has increased in elderly and immunocompromised populations over recent decades.
Resistance and therapeutic implications
- Remains universally susceptible to penicillin, which is the antimicrobial of choice for confirmed infections.
- Resistance to macrolides and clindamycin has been reported in a variable proportion of isolates, requiring susceptibility testing before use.
- Combination therapy with clindamycin is considered in severe invasive infection to reduce toxin production.
Bench and reporting notes
- Beta-hemolysis on blood agar and Lancefield serologic grouping (group C or G) aid routine identification.
- Differentiation of Streptococcus dysgalactiae subsp. equisimilis from other beta-hemolytic species requires supplementary biochemical tests or mass spectrometry.
- Double-disk diffusion (D-test) clindamycin susceptibility testing is recommended before indicating the drug as monotherapy.
Sources
- CDC — Group A, C, and G Streptococcal infection
- EUCAST — Clinical breakpoints
- PubMed — Streptococcus dysgalactiae clinical review
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Streptococcus dysgalactiae (grupos C e G) in the lab?
Streptococcus dysgalactiae (grupos C e G) is identified through beta-hemolytic, catalase-negative, lancefield latex agglutination positive for group c or g, large colonies (> 0.5 mm), distinct from streptococcus anginosus group.
What are the intrinsic resistances of Streptococcus dysgalactiae (grupos C e G)?
This organism is naturally resistant to never report susceptibility to aminoglycosides alone, no confirmed penicillin resistance has been described — an r result requires repeat testing. These drugs should not be reported as susceptible.
Where is Streptococcus dysgalactiae (grupos C e G) commonly found?
It is typically associated with cellulitis, erysipelas, soft-tissue infection in diabetic patients, bacteremia, septic arthritis and pharyngitis in adults.
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