Group C & G Streptococci

Group C & Group G Streptococci:

Several species of streptococci that carry the Lancefield group C or G antigens occasionally cause infections similar to those of Str. pyogenes. Most of these species have their primary habitat in horses, cattle and pigs, but some strains have become adapted to the human host and then produce some of the virulence factors primarily associated with Str. pyogenes. They can cause epidemic sore throat, especially in communities such as schools, nurseries and institutions, often associated with consumption of unpasteurized milk. Group C streptococci have been associated with acute glomerulonephritis but not with rheumatic fever. The most important of the group C streptococci in human medicine is "Str. equisimilis" (noted to carry both C or G antigens).

β-haemolytic streptococci of large colony size (≥0.5 mm in diameter) can almost always be grouped with Lancefield antisera using latex agglutination or coagglutination directed against the cell wall carbohydrate of groups A, B, C, or G.

In many diagnostic microbiology laboratories, bacitracin disk susceptibility is also used as a screening test to separate group A streptococci from other pyogenes-like organisms. Studies employing the standard 0.04-unit bacitracin disk have demonstrated that only 6% to 8% of groups C and G β-haemolytic streptococci are susceptible. However, other investigators have found greater variation in the bacitracin susceptibility of these streptococcal strains.

Large colony-forming β-haemolytic strains not containing group antigens are rarely etiologic agents of human disease. Those possessing group antigens other than A, B, C, and G have been isolated primarily from animals and environmental sources and may be carried as the normal flora of the pharynx, vagina, or skin of wild or domestic animals. Rare infections in humans have been reported to be caused by serogroups E, L, M, N, and O.

Streptococcus suis ("viridans Streptococci")

Group G Streptococci:

Group C's:

• Str. dysgalactiae subsp. equisimilis [most common human isolate]
  • Sepsis in neutopaenic hosts, puerperal sepsis, nec fasc etc.
  • Usually related to an underlying disease
• Str. dysgalactiae subsp. dysgalactiae
• Str. equi subsp. equi
• Str. equi subsp. zooepidemicus [bovine mastitis, sheep etc., but consumption of unpasturized cheese and milk led to outbreaks of pneumonia, bacteraemia, endocarditis, also post strep GN in some cases].

Microbiology:

• Large beta haemolytic colonies on blood agar, differentiating them from the small, minute colonies of viridans Streptococci, which may also group with C.
• Large colony group C organims cause pharyngitis while anginosus (A, C, F or G) organisms do not.
• Str. dysgalactiae subsp. dysgalactiae may be alpha- beta- or non-haemolytic.
• May carry streptococcal pyrogenic exotoxins (SPE G), also may acrry genes encoding proteins from the group A streptococcal superantigen family.

Group G's:

• Normal part of human flora
  • GI, vaginal, oropharyngeal, skin
  • Human isolate: Str. dysgalactiae subsp. equisimilis
  • Animal isolate: Str. canis
  • Bacteraemia, pneumonia, cellulitis etc.
  • Severe infections include prosthetic joint infections.
  • Cellulitis or septic arthritis near injection sites lead to subsequent bacteraemia and haematogenous spread (esp. IVDUs)

Management:

• Usually penicillin sensitive, also to ceftrioxone
• Maybe macrolide (and clindamycin) resistant
• All are vanc sensitive so far.

AMH.