2: Strep

Question 1

general features of strep

Answer 1

G(+) chains 
catalase (-) 
split into groups: 
-GAS - b-hemolytic, S. pyogenes 
-GBS - a-hemolytic, perinatal sepsis/newborns, UTIs
-viridans - a-hemolytic, endocarditis 
-mutans - major cause of dental caries

Question 2

why do you not usually get Ab’s to simple strep with GAS?

Answer 2

too late for Ab’s - they take 7-10d to make, and simple strep infections are usually resolved by that time

Question 3

potential complications of severe strep throat w/ GAS

Answer 3

• erythrotoxin -> Scarlet fever
• Ag + Ab -> glomerulonephritis (2 weeks)
• cross-reacting Ab’s w/ heart valves -> rheumatic fever

Question 4

sx of strep throat

Answer 4

• beefy red appearance
• dysphagia
• pus on tonsils
• fever/ chills
• punctate abscess in tonsillar crypts
• peritonsillar, retropharyngeal abscesses

Question 5

what is strep infection characterized by, histologically?

Answer 5

• neutrophils!!

- more spread: cellulitis -> red, warm (as opposed to staph, which has localized collections of neutrophils)

Question 6

strep virulence factors

Answer 6

• cell wall polysaccharides/ capsules (M proteins) - prevent phagocytosis
• enzymes: streptokinase, streptolysin O, S - spread through tissues (cellulitis)
• erythrogenic toxins - skin rash (very red lesions)

Question 7

describe scarlet fever

Answer 7

• febrile exanthematous disorder, age 3-15
• erythrogenic toxin -> violaceous red rash on trunks (blotches over body, not raised)
• strawberry tongue
• later desquamation of skin
• associated with post-strep sequelae

Question 8

describe PSGN

Answer 8

• 1-2w after strep throat infection
• 4-5w after strep skin infection (impetigo)
• self-limited
• immune complex mediated
• may see signs of acute renal failure - oliguria, hematuria, HTN

Question 9

describe rheumatic fever

Answer 9

-weeks to months past strep infection
-worse with repeated infections
-acute: fever, joint disease, myocardial and valvular disease
-autoimmune rxn that cross-reacts w/ M Ag’s
-no bacteria present
-corresponds to streptolysin O levels in blood as a
measure of severity of infection
-chronic: long-standing damage to mitral and aortic valves
-thickening of leaflets

Question 10

describe strep skin infections

Answer 10

• cellulitis, pyoderma - extensive spreading redness, swelling, pain
• common infection of wounds or breaks in skin
• less localized than staph
• can involve subcutaneous tissues
• rare abscesses, some pustules
• rare - necrotizing fasciitis

Question 11

impetigo

Answer 11

• tends to crust on skin
• contagious skin infection in kids
• involves horny (superficial) layers of skin

Question 12

erysipelas (GAS, GCS)

Answer 12

• middle-aged persons
• warm climate (tropics)
• orange peel skin
• erythematous skin involvement without supporation (no crusting)
• raised, bright red lesion
• need to be careful if on face -> can lead to meningitis

Question 13

necrotizing fasciitis

Answer 13

• uncommon deep-seated soft tissue infection
• if scrotal/perianal form: Fournier’s gangrene
• pre-existing immunodeficiency, diabetes
• subcutaneous strep infection with necrosis that is taken over by anaerobes (gas formation on x-ray)
• mortality 50-70%
• tx: surgical debridement to prevent spread

Question 14

subacute bacterial endocarditis

Answer 14

• associated with S. viridans
• transient bacteremia following dental work
• left sided valvular endocarditis
• greatest risk in patients w/ previously damaged heart valves
• take prophylactic abx for dental work

Question 15

which group of strep causes puerperal sepsis?

Answer 15

GBS

Question 16

diagnosis of GAS: strep throat

Answer 16

• rapid strep test: GAS carb Ag
• confirmatory culture 12-48h always!
  
  • cat (-), tells you abx specificity

Question 17

diagnosis of GAS: rheumatic fever

Answer 17

anti-streptolysin O Ab titer (even though cross-reacting Ab’s are specific for M proteins)