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Term 4: Infectious Diseases > Strep Pneumoniae > Flashcards

Strep Pneumoniae 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 EBC = 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: Infectious Diseases (21 decks)

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