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CMBM Exam 3: Immunology > Streptococcus and Enterococcus > Flashcards

Streptococcus and Enterococcus Flashcards

1
Q

What are 5 morphological and general characteristics associated with streptococcus?

A
  1. Gram (+) occuring in chains or pairs
  2. Catalase (-)
  3. Usually encapsulated
  4. Part of the normal flora in the respiratory tract, GU and GI tract
  5. Antibiotic resistance less of a problem than compared to Staph
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2
Q

What 3 ways/tests do we use to classify Strep? Include pertinent information

A
  1. Serological properties (Lancefield Grouping): Based on major cell wall carbohydrates (A-W). Used clinically to identify medically important strains (A, B, C, F, and G)
  2. Hemolytic Patterns: 3 types alpha (incomplete hemolysis), beta (complete hemolysis), and gamma (no hemolysis)
  3. Biochemical (physiological) Properties: such as tolerance to high heat or salt concentration
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3
Q

What are 6 medically important Strep strains? Give examples for each group

A
  1. Group A: S. pyogenes (GAS)
  2. Group B: S. agalactiae (GBS)
  3. Group C and G: S. milleri, S. dysgalactiae
  4. Group D: Enterococcus (actually is a separate genus but contains group D antigen), and non-enterococcal Group D Strep is S. bovis
  5. Viridans: S. salivarius, S. mitis, S. sanquis, and S. mutans and very importantly S. pneumoniae
  6. Anaerobic: Peptostreptococci
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4
Q

What 3 types of diseases do GAS cause?

A

Causes both suppurative and non-suppurative diseases

  1. Bacterial pharyngitis (most common)
  2. Myonecrosis (life threatening)
  3. Acute rheumatic fever (ARF)
  4. Post-strep glomerulonephritis (PSGN)
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5
Q

What are 6 structural virulence factors (that is ones that are contained in the cell membrane/wall and are not secreted) of GAS?

A
  1. M Protein: inhibits C3b binding thus blocking phagocytosis => invasion (functions as adhesion protein)
  2. M-like proteins: Bind Fc portion of antibody
  3. Hyaluronic acid capsule: since humans make HA then it is not immunogenic and conveys an anti-phagocytic property
  4. C5a peptidase: prevents chemotaxis
  5. Adhesion proteins: lipotechoic acid (LTA), M protein, and F protein
  6. Invasion of epithelial cells: M and Sfbl
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6
Q

What are 3 types of extracellular products that function as virulence factors for GAS? Give specific examples

A
  1. Spreading factors: Streptokinases, DNases, and proteases
  2. Streptolysin S and O: damage cell membranes => hemolysis
  3. Streptococcal pyrogenic exotoxins (SpeA, B, C, and F): result from a prophage, act as superantigens, responsible for rash associated with scarlet fever
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7
Q

What are 4 skin/soft tissue infections associated with GAS?

A
  1. Impetigo (pyoderma)
  2. Erysipelas
  3. Cellulitis
  4. Necrotizing fasciitis (possibly accompanied by bacteremia)
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8
Q

What is Streptococcal Toxic Shock Syndrome (STSS)? How is it distinguished clinically from TSS caused by Staph?
What are some risk factors for STSS?
What determines whether a specific GAS strain will cause STSS?

A

It is very similar to TSS and usually presents as both an infection and intoxication since it is frequently associated with bacteremia and necrotizing fasciitis
Clinically TSS caused by Staph tends to stay more localized while STSS is more systemic
Risk factors include many immunocompromised patients such as those with HIV, cancer, diabetes, and IVDU
Those that contain the SpeA or SpeC prophage gene or have the M protein serotypes 1 or 3; or strains that produce a very copious mucoid capsule

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9
Q

What are 2 non-suppurative complications involving GAS, what suppurative condition do they normally follow and what are each of them characterized by?

A
  1. Acute rheumatic fever (ARF): usually follows a severe respiratory infection, characterized by: inflammation of the heart, joints, blood vessels, and subcutaneous tissue
  2. Post-Strep Glomerulonephritis (PSGN): follows either a respiratory or skin infection, characterized by: acute inflammation of renal glomeruli with edema, hypertension, dark urine, and proteinuria
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10
Q

What test will distinguish GAS from GBS?

A

Bacitracin sensitivity test
GAS is bacitracin sensitive
GBS is bacitracin resistant

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11
Q

What 4 tests can be used to diagnose Strep throat?

A
  1. Beta-hemolytic on blood agar
  2. Bacitracin sensitive
  3. Streptolysin O (ASO test): titer detects recent respiratory infection by S. pyogenes
  4. Anti-DNase B test for recent cutaneous infection
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12
Q

What condition is GBS most often associated with?

A

Sepsis and meningitis in newborns since GBS colonize the lower GI and GU tract with transient vaginal carriage

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13
Q

What is the best way/tests to diagnose a GBS infection?

A
  1. Gram stain of the cerebrospinal fluid (CSF)
  2. CAMP test: increased hemolysis on blood plates when grown with S. aureus
  3. PCR
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14
Q

Where in the body is Viridans Strep most often encountered?

A

Main facultative bacteria in the oral flora, but can also encounter in the GI and GU tracts

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15
Q

What 4 types of diseases do Viridans Strep cause?

A
  1. Dental caries (they metabolize sugars giving off acid which erodes the enamel)
  2. Sub-acute bacterial endocarditis: especially in pts with abnormal heart valves, dental caries, and intra-abdominal infections
  3. Bacteremia
  4. Abscesses in the brain, oropharynx, or peritoneal cavity
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16
Q

What hemolytic properties do Viridans Strep have?

A

They are composed of a heterogenous collection of alpha and gamma/non-hemolytic strains

17
Q

What are 4 identifying characteristics of S. pneumoniae?

A
  1. Gram (+) diplococci, lancet shaped in short chains
  2. Alpha hemolytic
  3. Optochin sensitive and lysed by bile
  4. Encapsulated with 94 serotypes (however we do have a polyvalent vaccine Prevnar 13 and 23)
18
Q

What are the 3 main virulence factors for S. pneumoniae?

A
  1. Capsule (basis for vaccine)
  2. Pneumolysin: exotoxin which creates pores in ciliated epithelial cells and phagocytes, activates compliment => migration of inflammatory cells => tissue damage
  3. Secretory IgA protease
19
Q

What 5 diseases does S. pneumoniae cause?

A
  1. Typical lobar pneumonia (pneumococcal pneumonia)
  2. Meningitis (mostly in children and young adults)
  3. Otitis media (middle ear infection)
  4. Sinusitis
  5. Bacteremia
20
Q

What 5 tests are used to diagnose S. pneumoniae?

A
  1. Microscopic analysis for lancet-shaped diplococcus
  2. Bile soluble (dissolves in bile)
  3. Optochin sensitive
  4. Quelling reaction to detect capsule (expose bacteria to certain antibodies and observe if swelling of the capsule occurs)
  5. Immunoassay detection of pneumococcal C polysaccharide in urine
21
Q

What are 4 characteristics of Enterococci?

A
  1. Gram (+) cocci, usually occurring in pairs
  2. Part of the normal intestinal flora
  3. Virulence is due to resistance to commonly used antibiotics (so infection occurs in immunocompromised patients or those treated with broad spectrum antibiotic)
  4. One of the most common causes of nosocomial infections
22
Q

How do enterococci clinically manifest, through what types of conditions?

A
  1. UTI (can gain access to blood)
  2. Nosocomial bacteremia
  3. Bacterial endocarditis
  4. Peritonitis (usually polymicrobial)
23
Q

How is enterococci identified? 3 ways

A
  1. Observe growth in high salt (6.5%) environment
  2. Observe growth at high temp (42C) environment
  3. Observe growth in presence of 40% bile salts
24
Q

How is an enterococci infection treated?

A

Usually synergistic combination of antibiotic therapy (aminoglycoside and a cell wall active antibiotic)
Can use vancomycin but resistance does exist

CMBM Exam 3: Immunology (21 decks)

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