Various haemolytic groups, GAS is beta haemolytic. Other groups of beta haemolytic identified by Rebecca Lancefield.
- Beta haemolytic Group B is seen in the genitourinary tract of women and is an important pathogen in neonates.
- Groups C and G both cause invasive disease, both have M proteins, more common throat carriage in developing countries. Maybe also responsible for acute rheumatic fever.
- Alpha-haemolytic (strep viridans) are associated with line infections and endocarditis.
- Gamma-haemolytic include enterococci, of which faecium is usually resistant to amoxicillin but faecalis is usually sensitive. Of note, some enterococci are now resistant to vancomycin (VRE).
M type proteins on GAS are the main virulence factors esp 1, 3. About 20 toxins, all superantigens. Antibodies to toxin are effective. Some HLA types appear more susceptible.
- Pharyngitis and tonsillitis
- Erysipelas – rapidly spreading skin infection with clear demarcation, can evolve over a few hours. Differential is staphylococcus.
- Post streptococcal nephritis
- Post streptococcal arthritis
- Necrotizing fasciitis
- Acute rheumatic fever, including Sydenhams chorea.
- Sepsis. Group A strep sepsis is provoked by varicella. A quarter of all invasive strep infections in kids follow chickenpox esp toxic shock, osteomyelitis. ?Shifts T helper cells from Th2 (antibody) to Th1 (cellular).
Culture from throat, skin etc.
ASO titre and DNAse B titres are not 100% sensitive, and high titres can persist after infection.
Group A streptococcus has never been resistant to penicillin! But doesn’t mean penicillin is the best treatment: Clindamycin shows superior killing (in animal models) – inhibits protein synthesis so works throughout cell cycle, cf penicillin where action only during replication. Will also inhibit toxins (in theory).
IVIG effective against toxins.
GAS vaccine? – danger of priming for rheumatic fever! New 26 valent, effective for sore throats and invasive disease, probably not long term effective or appropriate for preventing rheumatic fever.