Bacterial Upper Respiratory Infections

Question 1

most common agents responsible for diseases of the upper respiratory tract. i.e.nasopharynx, oropharynx, middle ear and paranasal sinuses, and epiglottitis

Answer 1

• Nasopharynx
  
  • rhinoviruses, coronaviruses, and other respiratory viruses,
• Oropharynx
  
  • Streptococcus pyogenes (group A streptococci),
  • Corynebacterium diphtheriae,
  • Epstein-Barr virus,
  • adenovirus, enterovirus.
  • Note: acute,initial HIV infection
• Middle ear and parasinuses
  
  • Streptococcus pneumoniae
  • Haemophilus influenzae non-typeable
  • Moraxella catarrhalis
  • group A streptococci
• Epiglottis
  
  • Haemophilus influenzae type b

Question 2

microbiological characteristics of Streptococcus pyogenes (GAS).
How is the organism is identified in the laboratory?

Answer 2

• Gram positive cocci that tend to occur in chains
• Catalase negative
• Beta hemolytic on blood agar plates
• Bacitracin sensitive
• Can test w/ commercially available test in which hyperimmune anti-A sera coupled to latex beads

Question 3

virulence determinants of group A streptococci

Answer 3

• M protein helps prevent phagocytosis
  
  • Antibodies to M protein can cross react w/ heart tissue and cause rheumatic fever
• Hyaluronic acid capsule:antiphagocytic; antibodies not protective
• Pyrogenic exotoxins: superantigens stim production of cytokines
  
  • Involved in Scarlet fever and TSS like syndrome
• Streptoysin O: O2 labile, antigenic, and hemolytic
  
  • Toxic to many cells
  • Antibodies to this is basis for ASO test
• DNAases: depolymerize cell free DNA in purulent lesions
  
  • Can also measure antibodies for these
• Streptokinase: lyses blood clots-helps bacteria spread
• C5a peptidase: degrades complement component C5a that attracts neutrophils

Question 4

Group A streptococci Clinical Presentation

Answer 4

• Pharyngitis- uncommonly Scarlet fever
  
  • Symptoms can include N/V/abdominal pain
  • Signs: inflammation of oropharynx; petechia on soft palate
• Pyogenic: pharyngitis, cellulitis, impetigo
• Toxigenic: scarlet fever, TSS-like syndrome
• Immunologic: rheumatic fever, acute glomerulonephritis

Question 5

Haemophilus influenze: Bacterial Characteristics

Answer 5

• Gram negative coccobacilli: curved ends on short rods
• Growth requirements – fastidious
  
  • requires X (hemin, heat stable)
  • Also requires V (NAD or NADP, heat labile)
  • Can be grown w/ S. aureus which provides factor V
• Both factors are provided in chocolate agar.
• Also, grows best in 5-10% C02.
• Transmitted by aerosol

Question 6

Haemophilus influenzae: Virulence Factor

Answer 6

• The type b capsule is polyribose-ribitol phosphate (abbreviated PRP or Hib)
• PRP capsule is antiphagocytic
• antibody against the capsular polysaccharide is protective against invasive infections by H. influenzae
• Produces IgA protease

Question 7

Haemophilus influenzae: Clinical Presentation

Answer 7

-Type b:
-meningitis
-epiglottis
-cellulitis
-acute pneumonia
Nonencapsulated:
-otitis media
-sinusitis
-conjunctivitis

Question 8

Haemophilus influenzae: Treatment

Answer 8

• Menigitis: ceftriaxone

- If suceptible, tx with ampicillin

Question 9

Haemophilus influenzae: Vaccine

Answer 9

• Several different Hib-conjugate vaccines are licensed (e.g. Hib coupled with diphtheria toxoid)
• PRP-conjugate vaccine, primary series in infancy, effective against type b disease but not versus nonencapsulated
• Must conjugate b/c children immune sys not effective against polysaccharide, but can mount response to protein like the protein toxoid

Question 10

Corynebacterium diphtheriae: Biological characteristics

Answer 10

• Gm+ rods
• form “Chinese letters” Club shapped
• non-motile, non-spore-forming
• Grow on special culture media containing tellurite.
• Catalase positive
• Lab diagnosis w/ metachromatic (blue and red) grandules in the rods
• Elek test for toxin

Question 11

Corynebacterium diphtheriae: Virulence Factor

Answer 11

• Causes diphtheria via exotoxin
• Encoded by beta prophage
• Exotoxin inhibits protien synthesis via ADP ribosylation of elongation factor 2

Question 12

Corynebacterium diphtheriae: Clinical Presentation

Answer 12

• Symptoms: pseudomembranous pharyngitis
  
  • Grayish-white membrane
• Lymphadenopathy

Question 13

Corynebacterium diphtheriae: Treatment and Prevention

Answer 13

• Treatment = passive therapy with horse anti-toxin
  
  • Antibiotics eradicate organism
• Prevention= immunize with toxoid