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Infectious Disease > Streptococci > Flashcards

Streptococci Flashcards

1
Q

Streptococci occur in

A

Gpos cocci occuring in chains

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2
Q

All Streptococci are

A
  • Catalase negative
  • Gpos cocci occuring in chains
  • check for hemolysis pattern
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3
Q

Types of Streptococci

6 listed

A
  • Streptococcus pyogenes (Group A)
  • Streptococcus agalactiae (Group B)
  • Streptococcus pneumonae
  • Streptococcus viridans
  • Enterococcus (Group D)
  • Streptococcus bovis
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4
Q

Group A strep

A

Streptococcus pyogenes

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5
Q

Group B strep

A

Streptococcus agalactiae

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6
Q

Group D strep

A

Enterococcus

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7
Q

Features of Streptococcus pyogenes

A
  • Group A strep
  • Pyrrolidonyl arylamidase (PYR) positive
    • Substrate (L-napthylamide-beta-napthylamide) hydrolyzed by bacterial enzyme to beta-naphthylamide
    • can be detected by color change with detection reagent
  • M protein virulence factor
    • inhibits phagocytosis
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8
Q

Strep pyogenes illnesses

A
  • infections
    • Pharyngitis (strep throat)
    • skin: Cellulitis, impetigo
  • Toxin-mediated disease
    • Scarlet fever
    • Necrotizing fasciitis
    • Toxic Shock Syndrome
  • Immune-disease
    • Rheumatic fever
    • Post-strep glomerulonephritis
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9
Q

Strep pharyngitis

A
  • 15-30% of pharyngitis is due to S. pyogenes
    • most cases are viral
  • important to identify and treat S. pyogenes
    • prevent transmission
    • limit symptoms and severity
    • prevent Rheumatic fever
  • Dx
    • Throat culture
    • Rapid antigen test (useful if positive)
  • Tx
    • Penicillin
    • Amoxicillin
    • Cephalosporins
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10
Q

Strep pyogenes skin infections

A
  • cellulitis and impetigo
  • can also be caused by Staph aureus so antibiotics need to cover both
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11
Q

Strep pyogenes Scarlet fever

A
  • Rash following pharyngitis
  • Skin reaction to ***erythrogenic toxin***
  • gene for toxin transferred by lysogenic bacteriophage (not found in bacterial genome)
  • symptoms
    • fever
    • sore throat
    • diffuse red rash
    • strawberry tongue (can also get from Kawasaki Disease)
    • also many small papules (“sandpaper” skin) (palms and soles usually spared)
    • starts on the head/neck -> expands to cover the trunk
    • Eventually skin desquamates (palms and soles usually spared)
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12
Q

Differentiating Scarlet fever from Kawasaki disease

A

Look for a sore throat to determine Scarlet Fever

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13
Q

Infectious rashes that involve the palms and soles

A
  • Syphilis
  • RMSF
  • Coxsackie virus
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14
Q

Necrotizing fasciitis

A
  • Caused by Strep pyogenes strains that produce streptococcal pyrogenic exotoxin
  • Infection of deep tissues
    • muscle fascia/subcutaneous fat
    • Streptococcal pyrogenic exotoxin released
  • fulminant and deadly
    • infection spreads along the muscular fascia and requires surgical debridement
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15
Q

Necrotizing fasciitis toxin

A

Strep pyogenes that produce streptococcal pyrogenic exotoxin

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16
Q

Type 1 Necrotizing fasciitis

A
  • polymicrobial (Bacteroides, Clostridium, etc. anaerobes)
  • occurs in diabetics, immunocompromised, post-surgery
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17
Q

Type 2 Necrotizing fasciitis

A
  • Group A strep
    • sometimes Staph
  • Occurs in otherwise heallthy people after skin injury
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18
Q

Classic case of Type 2 Necrotizing fasciitis

A
  • minor skin trauma
  • redness/warmth (can be confused with cellulitis)
  • pain out of proportion to exam
  • fever
  • hypotension
19
Q

Rheumatic fever

A
  • A type II autoimmune reaction
  • Follows Group A strep pharyngitis infection
  • Streptococcus -> anti-strep antibodies cross react with tissue-antigens
  • Dx: Jones criteria
20
Q

Rheumatic fever pathology

A
  • Aschoff bodies (form of granuloma) ***Pathognomonic for rheumatic carditis***
  • Anitschkow’s cells
  • Elevated ASO titers (Anti-streptolysin O antibodies)
21
Q

Jones Criteria

A
  • Major
    • carditis
    • polyarthritis
    • chorea
    • Erythema marginatum
    • subcutaenous nodules
  • Minor
    • fever
    • arthralgia
    • prior RF
    • elevated WBC, ESR, CRP
    • prolong PR interval

Must have evidence of strep infection and 2 major or 1 major & 2 minor to diagnose Rheumatic fever

22
Q

Clues to diagnosing Rheumatic fever

A

Sore throat or URI followed by joint pain, new murmur

23
Q

Tx of Rheumatic fever

A

Penicillin (often indefinitely for prevention of recurrent infection)

24
Q

Cardiac involvement of Rheumatic fever

A

Acute RF -> severe valve disease, heart failure

Later -> mitral stenosis (rarely aortic or tricuspid valves)

25
Q

Post-streptococcal GN

A
  • Nephritic syndrome 2-3 weeks after GAS infection
  • Nephritogenic strains of strep
    • bacteria with particular M protein subtypes cause nephritis
      • specific subtypes are associated with RF and others with post-streptococcal GN (so pts get on or the other but not both)
26
Q

Strep agalactiae features

A
  • Group B strep
  • Beta-hemolytic (like GAS)
  • Makes CAMP factor
    • Staph aureus makes beta-hemolysin
    • CAMP factor enhances lysis by beta-hemolysis
  • hydrolyzes hippurate
    • alters the color of hippurate test
  • Colonizes the vagina
  • causes infections in newborns
    • babies infected in utero or during birth
    • Pneumonia, meningitis, sepsis
  • Pregnant women screened at 35-37 weeks
  • GBS+ pregnant women recieve prophylaxis
    • 4 hours pre-delivery
    • Penicillin, ampicillin or cefazolin
27
Q

Beta-hemolytic strep

A
  • GAS (Strep pyogenes)
  • GBS (Strep agalactiae)
28
Q

Rapid Strep agalactiae test

A

Hippurate test

29
Q

Step pneumonia features

A
  • “Lancet-shaped” gram (+) cocci
  • Makes IgA protease
  • Key virulence factor: polysaccharide capsule
    • prevents phagocytosis
    • basis of vaccine from capsular material
    • Asplenic patients at risk for sepsis
      • splenectomy
      • Sickle cell anemia
30
Q
A
31
Q

Step pneumonia illnesses

A
  • Lobar pneumonia
  • Meningitis
  • Ottitis media
  • Sinusitis
32
Q

Strep viridans features

A
  • group of similar bacteria
  • No strep Lancefield grouping
  • Normal mouth flora
33
Q

Strep viridans illnesses

A
  • Dental caries (Strep mutans)
  • Subacute endocarditis (Strep sanguis)
34
Q

Subacute endocarditis

A
  • caused by Strep sanguis
  • slow-onset of symptoms
  • less sick pts
  • often affects abnormal vales
  • Dextran -> fibrin
  • Requires endothelial damage
  • Mitral valve prolapse
  • PEARL= Recent Dental Procedure
35
Q

Dextran?

A

Strep viridans

36
Q

Types of enterococcus

A
  • E. faecalis
  • E. faecium
37
Q

Features of Enterococcus

A
  • normal colonic bacteria
  • Group D Strep (Lancefield Group D)
  • Resistant to penicillin
  • Vancomycin resistant Enterococcus (VRE)
    • dangerous hospital acquired infection
38
Q

Enterococcus illnesses

A
  • UTIs
  • Endocarditis (rare)
  • VRE (Vancomycin Resistant Enterococcus)
    • dangerous hospital acquired infection
39
Q

Antibiotics for Enterococcus

A
  • relatively resistant to cell wall agents (penicillin, ampcillin, vancomycin)
  • Impermeable to aminoglycosides
  • For bacteremia us synergystic therapy
    • Vancomycin/Gentamycin
    • Ampicillin/Gentamycin
  • For VRE use
    • Linezolid
    • Daptomycin
  • Micro lab sensitivities are very important for therapy
40
Q

Enterococcus UTIs

A
  • Often hospital acquired (associated with catheters)
  • Removal of catheter alone may cure infection
  • Urinalysis: negative for nitrites
41
Q

UTIs negative for nitrites

A

only 2 bacteria do this

  • Staph saprophyticus
  • Enterococcus
42
Q

Enterococcus Endocarditis

A
  • Rare cause of endocarditis
  • usually caused by GU tract manipulation
    • TURP procedure for enlarged prostate
    • Cystoscopy
  • Vancomycin/Gentamycin often used for empiric therapy before culture data is available
43
Q

Strep bovis features

A

normal colonic bacteria

44
Q

Strep bovis illnesses

A
  • Rare cause of bacteremia/endocarditis
  • endocarditis or bacteremia infection is strongly associated with colon cancer (breakdown of the colon wall is how bovis got into the blood stream)

Infectious Disease (82 decks)

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