Streptococci I

Question 1

Streptococci anaerobic or aerobic?

Answer 1

Facultative anaerobes (can grow in both)

Question 2

a, b, y hemolysis

Answer 2

a - partial hemolysis ex: viridans streptococci, streptococcus pneumoniae b - total hemolysis, no intact RBCs (groups A,B, C, and G, sreptococcus iniae) y - not really hemolysis (strep gallolyticus, enterococcus, milleri group)

Question 3

How to differentiate between a streptococci?

Answer 3

Strep pneumoniae are susceptible to optochin (death disc) and soluble in bile salts while viridans strep are not

Question 4

How to differentiate between b-hemolytic strep?

Answer 4

Susceptibility to bacitracin (s pyogenes is suseptible while others group B, C, and G are resistant) when you think B-hemolytic strep…use the B (bactracin) test!

Question 5

What does Lancefield classification rely on?

Answer 5

immunologic classification based on differences in cell wall carbohydrates (Groups A, B, C, D, F and G)

Question 6

Hyaluronic acid capsule

Answer 6

non-antigenic (indistinguishable from human connective tissue hyaluronate). antiphagocytic (interferes with PMN phagocytosis)

Question 7

M proteins

Answer 7

immunologically distinct group A, exist on fimbriae, antiphagocytic prevents complement

Question 8

C- carbohydrate

Answer 8

group polysaccharide, basis of Lancefield groupings,

Question 9

Lipoteichoic acid

Answer 9

functions as adherence ligand

Question 10

Muramyl dipeptide

Answer 10

aka peptidoglycan - phage receptor, endotoxin-like activity

Question 11

Pyrogenic exotoxins A, B, C, D) aka erythrogenic toxins aka SPEA, SPEB, SPEC etc,

Answer 11

toxins responsible for scarlet fever rash….antibodies to these protect against repeat infection

Question 12

Streptolysin O

Answer 12

oxygen-llabile hemolysin that is neutralized by cholesterol in skin. Anti titers used to Dx rheumatic fever, less useful following skin infections

Question 13

Streptokinase

Answer 13

activates plasminogen to disrupt blood clots (can be used therapeutically in patients with coronary artery occlusion)…not really used much anymore since you can get allergic rxns

Question 14

Hyaluronidase

Answer 14

contributes to pathogenicity by allowing spread of infection through tissues

Question 15

DNAse

Answer 15

antigenic, antiDNAse used dx after skin infections

Question 16

Which class of MHC are presented by APCs and cleaved into peptides

Answer 16

Class II MHC

Question 17

How can streptococcus pyogenes cause disease?

Answer 17

• direct infection with tissue destruction - toxin production - immunological response

Question 18

pharyngitis/tonsillitis (“strep throat”)

Answer 18

-abrupt onset of sore throat with malaise, fever, and headache -edema and lympphoid hyperplasia, tonsil exudates, enlarged nodes, temperature greater than 101F

Question 19

What is the “gold standard” for dx of strep throat?

Answer 19

Throat culture! can also use rapid antigen tests

Question 20

Scarlet fever

Answer 20

“strawberry tongue”, “sandpaper rash”, results from infection due to strain of S. pyogenes that produces erythrogenic toxin as a consequence of being infected by a page

Question 21

Pyoderma (impetigo)

Answer 21

superficial skin infection with papule-vesicle-pustule crust stages due to S pyogenes, S aureus…spreads within households on fomites

Question 22

Cellulitis

Answer 22

vast majority due to S pyogenes. Diffuse inflammation of both skin and subcutaneous tissues with redness and tissue edema

Question 23

lymphangitis

Answer 23

charactersitic of S pyogenes soft tissue infections, lymph node tenderness may precede soft tissue symptoms

Question 24

erysipelas

Answer 24

form of celluitits characterized by diffuse lymphangitis in which infection actively spreads along lymphatics with redness and pain at advancing margins

Question 25

Cellulitis/erysipelas can follow years after what procedures?

Answer 25

• Bypass. (CABG) can recurrent…interrupts drainage - axillary lymph node dissection for breast carcinoma pretty much anything that disrupts lymph drainage

Question 26

How to define streptococcal toxic shock syndrome?

Answer 26

Isolate group A strep (S. pyogenes) from a normally sterile site (i.e. blood, CSF,) or a non sterile site, hypotension (systolic under 90 mmHg), have organ systems involved (renal, liver, respiratory, etc)

Question 27

acute rheumatic fever

Answer 27

immunologic response towards S. pyogenes (maybe M proteins) that occurs EXCLUSIVELY following pharyngitis Major manifestations: carditis, polyarthritis, chorea, erythmea marginatum, subcutaneous nodules (not all of these may be present when you see patient)

Question 28

post-streptococcal glomerulonephritis

Answer 28

occurs following skin OR pharyngeal infetions due to deposition of immune complexes in kidneys. Manifestations: edema, of face and extremities, hematuria, hypertension, decreased complement, abormal urinary sediment

Question 29

guttate psoriasis

Answer 29

occurs 1-2 weeks following infection with group A strep. Increased frequency of Vb2 T cells in their skin lesions…ACTIVE LESIONS

Question 30

How to test for acute rheumatic fever?

Answer 30

Anti streptolysin O titers (ASO)