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Flashcards in Streptococcal Species Deck (33)
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what is the most common cause of pharyngitis

viral; most commonly diagnosed bacterial cause is Group A strep


How are strep species classified

based on hemolysis, Lancefield groups (based on C carbohydrate in cell wall), Type specific antigens


Group A strep

S. pyogenes


Group B strep

S. agalactiae
- primarily infection of babies (pneumonia, meningitis, sepsis)
- 20-25% prego women colonized in rectum/vagina, so babies can acquire through birth-- very high mortality
- Gropu B vaccine given during pregnancy
- beta hemolytic, lipoteichoic acid, polysaccharide capsule
- NO M, T, R proteins
- Ab to polysaccharide capsule


what is purpose to treat streptococcal pharyngitis

to prevent rheumatic fever, not necessarily to get rid of pharyngitis


Group D strep

-kinda 2 categories but not really called Group D anymore-- Enterococci and non-enterococci group D (S. bovis)



- formerly group D-- colonize nl GI tract
- usually opportunistic
- Adults: nosocomial infections-- UTI, bacteremia, biliary tract infections, line sepsis, endocarditis
- Children: nosocomial bacteremia
- inducible transferable high level vancomycin resistance (VRE)
- can grow in 6.5% NaCl
- variable hemolysis
- E. faecalis more common but E. faecium more dangerus


Major virulence factor of group A strep

M protein-- contributes ability to adhere by binding lipoteichoic acid (LTA) in correct orientation
- in the form of fine fimbriae
- 80 serotypes
- certain M types associated with predilection for pharyngeal infection or skin infection, as well as possible non-suppurative complications (ARF, AGN)


Group A spreading factors

Streptokinase, hyaluronidase, DNAse, proteinase


Which type of group B strep in newborn can be prevented b y giving antibiotics prior to delivery

early onset disease


alpha hemolytic strains

-S. pneumoniae
-Viridans group (S. mutans, S. sanguinis)

- have green ring around colony--biliverdin/heme degradation products


Streptococci Metabolism

- Gram positive
- Catalase negative
- aerotolerant
- ferment carbohydrates to lactic acid
- fastidious nutritionally (hard to grow)
- blood/serum enhances growth


beta hemolytic bugs

Group A, Group B,


M protein

major virulence factor present on group A strep (S. pyogenes)
- phagocytes ingest and kill strains without this protein but can't kill bugs with it
- Ab against M-protein allows killing but is serotype specific
- N terminus where variation occurs


Group A Antigens

- capsule (hyaluronic acid)
- cell wall (surface protein--M, T, R)
- Group Carbohydrate (A)
- Mucopeptide
- glycerol teicholic acid
- cytoplasmic membrane


GAS extracellular virulence products

- Streptolysin O (hemolysin- antigenic)
- Streptolysin S (hemolysin--non antigenic)
- Pyogenic exotoxins (A-C; immunosuppressive and enhance susceptibility to endotoxin shock)
- Spreading factors (hyaluronidase, DNAse, proteinase, streptokinase)
- streptokinase lyses clots


Streptolysin O

- Oxygen labile hemolysin
- binds RBC, polymerizes, forms pore in membrane--causes hemolysis)
- Antistreptolysin O (ASO) antibody increases after infection


Diseases caused by group A strep

- Pyogenic (pharyngitis, osteomyelitis, cellulitis, impetigo, erysipelas)
- Toxigenic (Toxic chock-like syndrome, scarlet fever, necrotizing fasciitis)
- Immunogenic (rheumatic fever, acute glomerulonephritis)


Acute Rheumatic Fever

Nonsuppurative complication of S pyogenes 3-6 weeks after pharyngitis infection (NOT skin) but bug not recovered from site inflammation
- inflammation of heart valve, skin, joints, CNS
- Best model = autimmune disease-- M3 and M18 strains associated with ARF; genetic predisposition (HLA and B cell alloantigen)--think genetically programmed abnormal immune response to common infection
- JONES criteria
(Joint polyarthritis, Carditis, Nodules (subcutaneous) erythema marginatum--annular arythema, Syndenham chorea)


Scarlet Fever

scarlet rash with sandpaper like texture, strawberry tongue, circumoral pallor, subsequent desquamation
- due to infection with strains producing pyrogenic exotoxins


Post streptococcal glomerulonephritis (PSGN)

- Nonsuppurative complication from S. pyogenes 2-4 weeks after infection but don't recover organism from site of inflammation
- some M types associated with increased
- Best model = immune complex disease (Type III sensitivity reaction)-- complexes trapped below glomerular basement membrane-- complement deposition and neutrophil recruitment results in kidney damage
- Dark urine, facial swelling from edema
- can be after pharyngitis and skin infections


CAMP factor

produced by gropu B-- enlarges area of hemolysis formed by S. aureaus
- distinguishes S. galactiae


GBS virulence factors/toxins

Neuraminidase, C protein, Beta hemolysin, Protease, Hyaluronidase


Non-enterococcus Group D strep

- i.e. Strep bovis
- colonizes gut, upper respiratory tract, GU, skin
- opportunistic! (intra-abdominal infections, TUI, abscesses post appendicitis/diverticulitis/other GI dz, endocarditis/heart valve infection; in-dwelling IV catheter infection common

- can cause bacteremia with subacute endocarditis
- associated with colon cancer
- can grow in bile but NOT 6.5% NaCl (diff from Enterococci)


Pus in strep vs Staph

strep is more watery, thin vs thicker pus from staph


Which nonsuppurative complications does antibiotic therapy prevent

- ARF, probably not APSGN


nephitogenic GAS strains

M12, M4, M49


Viridans strep

- alpha hemolytic
- S. salivarius, S pyogenis sanguis, S. mitis, S mutans
- mutans assd with dental caries
- bacterial endocarditis from ability of strains to adhere to previously damaged valves (about 50% cases due to viridans strep)


Group G strep

similar to goup A
- many produce streptolysin O, streptokinase
- several M proteins
- uncommon cause of pharyngitis; can cause othe rinfections
- ARF doesn't occur but APSGN can


Group C strep

animal pathogens with occasional human disease
- some pharyngitis oubreaks
- streptolysin O produced
- No ARF but occasional APSGN