Streptococci I

Question 1

Streptococcus

Gram
Oxygen use
Shape/Configuration

Answer 1

Gram +

Facultative anaerobes - grow aerobically and anaerobically

Spherical - chains or pairs

Question 2

Alpha-hemolysis - what tests do you run to distinguish between alpha-hemolytic bacteria?

Answer 2

Partial hemolysis of RBC’s - green color due to hemoglobin reductant

Optochin sensitivity and bile solubility

Question 3

Beta-hemolysis - what tests do you run to distinguish between beta-hemolytic bacteria?

Answer 3

Complete hemolysis with no intact RBC’s

Bacitracin susceptibility

Question 4

Gamma-hemolysis - what tests do you run to distinguish between gamma-hemolytic bacteria?

Answer 4

Misnomer - no hemolysis

Bile esculin test - Growth on bile esculin agar, hydrolyze esculin and turn agar black

Question 5

How can you differentiate between S. pneumoniae and Viridans streptococci?

Answer 5

Optochin disks - S. pneumoniae are susceptible, Viridans are not

Bile salts - S. pneumoniae are soluble, viridans are not

Question 6

How can you differentiate between B-hemolytic streptococci?

Answer 6

Susceptibility to bacitracin disks

S. pyogenes is susceptible, groups B,C,G are resistant

Question 7

What is Lancefield classification used for?

Answer 7

Classification based on differences of cell wall carbs (c-carbohydrates)

Used for b-hemolytic strep initially, but also for others

Question 8

Hyaluronic acid capsule

Answer 8

non-antigenic (indistinguishable from hyaluronate in human ground substance), antiphagocytic by interfering with PMNs

Question 9

M-proteins

Answer 9

Exist on fimbriae

Antiphagocytic by preventing interaction w/ complement, associated with invasive disease

Question 10

C-carbohydrate

Answer 10

Group polysaccharide - basis for Lancefield groupings

Antigenicity depends on terminal sugar residue on side chains of polysaccharide

Question 11

Muramyl dipeptide (peptidoglycan)

Answer 11

Structural component, phage receptor, endotoxin-like activity

Question 12

Lipoteichoic acid

Answer 12

Adherence ligand - polyglycerophosphates

Question 13

What extracellular products do streptococci produce?

Answer 13

• Pyrogenic/erythrogenic exotoxins A,B,C, D aka streptococcal superantigen - hyperactivate T cells
• Streptolysin O - hemolysin, neutralized by cholesterol
• Streptokinase - disrupts blood clots by activating plasminogen
• Hyaluronidase - spread of infection by destroying human hyaluronic acid
• DNAse - antigenic; anti-DNAse B titers used diagnostically, especially following skin infections b/c DNAse is not bound in skin by cholesterol

Question 14

What three ways can disease manifest with S. pyogenes infection?

Answer 14

• Direct infection w/ tissue destruction
• Toxin production
• Immunological response to infection (cross-reaction Abs, superantigen, immune complex deposition)

Question 15

S. pyogenes pharyngitis (strep throat)- symptoms

Answer 15

sore throat, malaise, fever, headache

Enlarged, red tonsils w/ exudates, tender, enlarged mandibular nodes, red pharynx

Question 16

What is gold standard for diagnosis of streptococcal pharyngitis/strep throat?

Answer 16

Throat culture

Rapid Ag tests are not as sensitive

Question 17

What is scarlet fever?

Answer 17

Results from S. pyogenes infection that produces erythrogenic toxin as a result of being infected by a phage

Strawberry tongue, sandpaper rash

Question 18

Pyoderma/impetigo

Answer 18

Superficial skin infection with papule-vesicle-pustule-crust stages

S. pyogenes, S. aureus

Question 19

Cellulitis/lymphangitis

Answer 19

S. pyogenes

Cellulitis: Diffuse inflammation of both skin & subcutaneous tissues w/ redness and tissue edema

Lymphangitis: redness following lymph path

Question 20

Erysipelas

Answer 20

Form of cellulitis - diffuse lymphangitis of skin in which infection actively spreads along lymphatics, with redness & pain at advancing margins

Question 21

What procedures are streptococcal cellulitis/erysipelas associated with?

Answer 21

Saphenous vein harvesting for CABG

Axillary lymph node dissection for breast carcinoma

Question 22

Toxic Strep Syndrome

Answer 22

Group A Streptococcus (S. pyogenes)

Caused by super-antigen/pyogenic exotoxins –> polyclonal T cell activation

Hypotension, can involve renal impairment, coagulopathy, liver, respiratory distress, erythematous macular rash that can desquamate, soft tissue necrosis

Question 23

Rheumatic fever - what is it/what do you treat it with?

Answer 23

immunologic response towards S. pyogenes that occurs exclusively following streptococcal pharyngitis

Question 24

What are Jones criteria for diagnosis of acute rheumatic fever?

Answer 24

MAJOR
- Carditis - appearance of new murmur
- Polyarthritis
- Chorea
- Erythema marginatum - painless, red, blanching dermatitis
- Subcutaneous nodules
MINOR
- Arthralgia, arthritis - most common (LE joints)
- Fever

Question 25

Glomerulonephritis

Answer 25

Occurs following skin or pharyngeal infection

Due to deposition of immune complexes in glomeruli of kidneys

Manifests as: edema of face & extremities, hematuria, HTN, decreased complement levels, abnormal urine

Question 26

Guttate Psoriasis

Answer 26

Post-infection with Group A strep (S. pyogenes)

Involves exotoxin C - superantigen stimulation of T cells in skin lesions

Splotchy, red rash - dots - vascular alterations, keratinocyte proliferation w/ activation of Ag-producing cells, lymphokine secretion by activated T cells and neutrophil infiltration

Question 27

What test do you run to identify Group A strep/rheumatic fever? When are they less useful?

Answer 27

Anti-streptolysin O titers (ASO)

Less useful following skin infections b/c streptolysin O is bound by cholesterol in the skin and is not available for presentation to Ab producing cells

Question 28

Superantigens (a type of pyogenic exotoxin)

Answer 28

Do not require processing by Ag-presenting cells - bind directly with class II MHC molecules outside conventional Ag-binding groove

Superantigen-MHC complex binds only to the Vbeta variable elements of TCRs

Question 29

What type of hemolysis do Group A strep (S. pyogenes) exhibit?

Answer 29

Beta-hemolysis

Question 30

What strep group’s streptokinase is used therapeutically to lyse blood clots?

Answer 30

Group C

Question 31

What strep exotoxin is a cysteine protease that degrades ECM components like fibronectin to help spread infection?

Answer 31

SPEB

Question 32

Streptococcus pyogenes

Strep group
Type of hemolysis
Bacitracin sensitivity
Diseases
Diagnostic Indicator
Treatment

Answer 32

• Group A
• Beta-hemolytic
• Bacitracin sensitive
• Streptococcal pharyngitis (strep throat), scarlet fever, cellulitis/erysipelas, pyoderma (impetigo), toxic strep syndrome, rheumatic fever
• (+) throat culture or EIA, elevated or rising ASO titers (anti-streptolysin O)
• Penicillins and cephalosporins, long-term prophylactic penicillin

Question 33

Viridans streptococci

Type of hemolysis
Optochin sensitivity
Diseases

Answer 33

• Alpha-hemolytic
• Optochin resistant
• Dental caries, endocarditis

Question 34

Streptococcus pneumoniae

Type of hemolysis
Optochin sensitivity
Catalase
Bile salts
Diseases

Answer 34

• Alpha- hemolytic
• Optochin sensitive
• Catalase negative
• Bile salt soluble
• MOPS - meningitis (sporadic), otitis media, pneumonia, sinusitis (acute, purulent)