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Infectious Disease Unit 1 > Streptococcal Species > Flashcards

Streptococcal Species Flashcards

1
Q

what is the most common cause of pharyngitis

A

viral; most commonly diagnosed bacterial cause is Group A strep

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2
Q

How are strep species classified

A

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

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3
Q

Group A strep

A

S. pyogenes

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4
Q

Group B strep

A

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
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5
Q

what is purpose to treat streptococcal pharyngitis

A

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

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6
Q

Group D strep

A

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

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7
Q

Enterococci

A
  • 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
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8
Q

Major virulence factor of group A strep

A

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)
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9
Q

Group A spreading factors

A

Streptokinase, hyaluronidase, DNAse, proteinase

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10
Q

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

A

early onset disease

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11
Q

alpha hemolytic strains

A
  • S. pneumoniae
  • Viridans group (S. mutans, S. sanguinis)
  • have green ring around colony–biliverdin/heme degradation products
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12
Q

Streptococci Metabolism

A
  • Gram positive
  • Catalase negative
  • aerotolerant
  • ferment carbohydrates to lactic acid
  • fastidious nutritionally (hard to grow)
  • ## blood/serum enhances growth
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13
Q

beta hemolytic bugs

A

Group A, Group B,

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14
Q

M protein

A

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
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15
Q

Group A Antigens

A
  • capsule (hyaluronic acid)
  • cell wall (surface protein–M, T, R)
  • Group Carbohydrate (A)
  • Mucopeptide
  • glycerol teicholic acid
  • cytoplasmic membrane
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16
Q

GAS extracellular virulence products

A
  • 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
17
Q

Streptolysin O

A
  • Oxygen labile hemolysin
  • binds RBC, polymerizes, forms pore in membrane–causes hemolysis)
  • Antistreptolysin O (ASO) antibody increases after infection
18
Q

Diseases caused by group A strep

A
  • Pyogenic (pharyngitis, osteomyelitis, cellulitis, impetigo, erysipelas)
  • Toxigenic (Toxic chock-like syndrome, scarlet fever, necrotizing fasciitis)
  • Immunogenic (rheumatic fever, acute glomerulonephritis)
19
Q

Acute Rheumatic Fever

A

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)
-

20
Q

Scarlet Fever

A

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

21
Q

Post streptococcal glomerulonephritis (PSGN)

A
  • 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
22
Q

CAMP factor

A

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

23
Q

GBS virulence factors/toxins

A

Neuraminidase, C protein, Beta hemolysin, Protease, Hyaluronidase

24
Q

Non-enterococcus Group D strep

A
  • 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)
25
Q

Pus in strep vs Staph

A

strep is more watery, thin vs thicker pus from staph

26
Q

Which nonsuppurative complications does antibiotic therapy prevent

A
  • ARF, probably not APSGN
27
Q

nephitogenic GAS strains

A

M12, M4, M49

28
Q

Viridans strep

A
  • 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)
29
Q

Group G strep

A

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
30
Q

Group C strep

A

animal pathogens with occasional human disease

  • some pharyngitis oubreaks
  • streptolysin O produced
  • No ARF but occasional APSGN
31
Q

GBS cell wall components

A
  • C carbohydrate
  • Lipoteichoic acids - -mediate adhesion
  • polysaccharide capsule in virulent forms with capular types Ia, Ib, II, III; resist phagocytosis (we develop Ab against capsule )
  • NO M, T, R Ag
32
Q

Extracellular products of GBS

A
  • neuraminidase, protease, betahemolysin, hyaluronidase

- CAMP factor – soluble protein enhancing hemolysis of S. aureus–used to ID group B strep

33
Q

forms of neonatal group B strep dz

A
  • Early onset within first 24 hrs– high mortality; all capsular types can cause this
  • Late onset after 24 hrs, usually 1 wk or later; almost all due to type III organisms
  • Vaccines have been produced but not all women produce Ab

Infectious Disease Unit 1 (19 decks)

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