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Term 4: ID practice > Strep Pneumo > Flashcards

Strep Pneumo Flashcards

1
Q

Which organism causes the majority of the cases of bacterial pneumonia, leading to hospitalization?

A

-Strep Pneumoniae

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2
Q

Is strep pneumoniae gram positive or negative?

A

Gram + (Blurple)

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3
Q

What is alpha hemolysis?

A

-when grown on agar that contains RBC’s, a molecule called alpha-hemolysin breaks hemoglobin down to a greenish pigment

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4
Q

What is the outermost layer of pneumococcus?

A
  • a polysaccharide capsule
  • contains peptidoglycan
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5
Q

What does PMN stand for?

A

-polymorphonuclear Leukocytes

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6
Q

Why is pneumococcus not readily ingested by PMNs?

A
  • The capsule is not recognized by receptors on PMN
  • in the absence of antibodies to specific capsular polysaccharide, they won’t be eaten by PMN
  • IgG to cell wall can’t be “seen” by PMN
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7
Q

Why are antibodies for the cell wall of pneumococcus not immune response inducing?

A

-The capsular polysaccharides are too long, and shield the Fc region of abs from PMNs

**Ig and complement diffuse through capsule, but capsule prevents PMN receptors from interacting with Fc of IgG.

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8
Q

What are the constituents of pneumococcus from the outside going in?

A
  • Polysaccharide capsule
  • Teichoic acid attached to lipid (lipoteichoic acid)
  • Choline-Binding Proteins
  • Peptidoglycan: Principal constiduent of cell wall
  • Pneumolysin
  • Autolysin
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9
Q

What factors cause decreased neutrophil function (chemotaxis, ingestion, killing)?

A
  • Diabetes Mellitus
  • Glucocorticosteroids
  • Renal insuficiency
  • Cirrhosis
  • Alcohol Ingestion
  • Genetic defects in PMN function
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10
Q

What factors can lead to defective IgG production?

A
  • Congenital
  • Acquired: myeloma, lymphoma, common variable immunodeficiency
  • HIV infection
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11
Q

How are splenectomies related to pneumococcal pneumonia?

A

-doesn’t predispose to infection

***but does predispose to overwhelming sepsis and shock in pneumococcal pneumonia

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12
Q

What is pneumolysin?

A
  • a major virulence factor produced by pneumococci
  • activates complement (inflammation)
  • Damages ciliated cells and PMN
  • reproduces changes of pneumonia in animals
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13
Q

What is the difference between epidemiology & pathogenesis?

A

Epidemiology = where the organism likes to hang out

Pathogenesis = how disease comes about

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14
Q

How is pneumococcal pathogenesis related to viral illness?

A
  • viral infection characterizes the major form of pneumococcal disease
  • virus messes up our normal anatomy (cilia), and pneumococcus gets stuck where its not supposed to be
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15
Q

Describe the microbiology of pneumococcus.

A
  • pairs or chains of elongated cocci
  • gram positive
  • colonies on blood agar surrounded by greenish zone (alpha-hemolysis)
  • colonies collapse in center (autolysin)
  • optochin susceptibility (ring of death around white thing)
  • dissolve in bile salts (definitive identification)
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16
Q

Which TLR does Teichoic acid of pneumococcus interact with ?

A

TLR 2 >>4

17
Q

What is important about Choline-binding proteins on pneumococcus?

A
  • they contribute to virulence
  • highly conserved between pneumococci strains
18
Q

What are bacterial cell wall peptidoglycans made of?

A

-alternating glucosamine and muramic acid in long chains

19
Q

Which TLR recognizes cell wall peptidoglycans?

A

TLR 2 >> 4

20
Q

What is the epidemiology of pneumococcus?

A
  • Confined to humans
  • lives in nasopharynx of healthy children/adults
  • contact or aerosol spread (facilitated by viral resp infection)
21
Q

What must first happen for bacteria to cause disease?

A
  • adhere to epithelial cells
  • bacterial surface constituents interact with surface molecules on mammalian cells, causing adherence
22
Q

What molecule on pneumococcus is responsible for adherence?

A

-Lipoteichoic acid

23
Q

What is colonization?

A

-when bacteria are present in sufficient number that we can find them by culture, AND, they cause no symptoms or signs of infection

**some organisms never colonize, mere presence indicates infection (TB)

24
Q

What is the pathogenesis of pneumococcus?

A
  • carried by secretions to space from which clearance is poor (damage/obstruction)
  • aspiration & inhalation = pneumonia

**organisms get where they do not belong, clearance is damaged, induce inflammation & disease results.

25
Q

What is the difference between inhalation and aspiration of an organism?

A
  • inhalation = breathing in aerosolized organisms
  • aspiration = mouth contents bypass glottis
26
Q

What factors decrease action of cilia and cough in the respiratory tract?

A
  • Smoking
  • inflammation
  • viral infection
  • Alcohol, codeine, morphine (suppress cough)
  • pollution
27
Q

How does pneumonia result from pneumococcus infection?

A
  • cocci reach alveoli, activating inflammatory response
  • WBCs attracted & capillary permeability increased
  • this means WPCs, plasma constituents, and RBC’s collect in alveoli = pneumonia infiltrate
28
Q

What factors predispose people to infection by pneumococcus?

A
  • Multifactorial: extremes of life, prior hospitalization, malnutrition, alcoholism
  • Decreased pulmonary clearance
  • diminished neutrophil function
  • defective IgG production
  • absence of spleen
29
Q

What are the common clinical manifestations of pneumonia?

A

(often preceded by viral infection)

  • Cough (90%)
  • Fever (90+%)
  • sputum production (variable)
  • chest pain (50-75%)
  • general appearance = look sick
  • can percuss and listen for rales, but xray is best
30
Q

What are the lab findings for pneumonia?

A

-High WBC, possible left shift

**reduction in WBC = overwhelming infection

  • opacity in chest xray
  • decreased O2 sat
31
Q

How is the diagnosis for pneumonia made?

A
  • gram stained sputum (90%)
  • Blood culture (bacteremia) (20%)
  • Urine antigen test (50%) = highly specific
32
Q

What other diseases are commonly caused by pneumococcus?

A
  • Acute otitis media
  • acute sinusitis
  • primary bacteremia
  • meningitis
  • acute cardiac events (23%)
33
Q

What are the vaccine options for pneumococcus?

A
  • Pneumovax (adult)
  • Protein-conjugated vaccine (children)
34
Q

How does the pneumovax vaccine work?

A

-contains capsular polysaccharide of 23 pneumococci serotypes

**not protective before age of 2 years, due to immature immune response to polysaccharides

35
Q

how does the protein-conjugated vaccine for pneumococcus work?

A
  • chemical conjugation of polysaccharide to a protein that alters the mode of presentation, so it works in babies
  • stimulates antibody in nasopharynx, thus preventing colonization
36
Q

What are the three main bacterial causes of acute otitis media?

A
  1. Strep pneumo (30%)
  2. H. influenzae (25%)
  3. Moraxella catarrhalis (15-20%)

Term 4: ID practice (22 decks)

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