Bacterial Upper Respiratory Infections Flashcards
most common agents responsible for diseases of the upper respiratory tract. i.e.nasopharynx, oropharynx, middle ear and paranasal sinuses, and epiglottitis
- 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
microbiological characteristics of Streptococcus pyogenes (GAS).
How is the organism is identified in the laboratory?
- 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
virulence determinants of group A streptococci
- 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
Group A streptococci Clinical Presentation
- 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
Haemophilus influenze: Bacterial Characteristics
- 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
Haemophilus influenzae: Virulence Factor
- 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
Haemophilus influenzae: Clinical Presentation
-Type b:
-meningitis
-epiglottis
-cellulitis
-acute pneumonia
Nonencapsulated:
-otitis media
-sinusitis
-conjunctivitis
Haemophilus influenzae: Treatment
- Menigitis: ceftriaxone
- If suceptible, tx with ampicillin
Haemophilus influenzae: Vaccine
- 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
Corynebacterium diphtheriae: Biological characteristics
- 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
Corynebacterium diphtheriae: Virulence Factor
- Causes diphtheria via exotoxin
- Encoded by beta prophage
- Exotoxin inhibits protien synthesis via ADP ribosylation of elongation factor 2
Corynebacterium diphtheriae: Clinical Presentation
- Symptoms: pseudomembranous pharyngitis
- Grayish-white membrane
- Lymphadenopathy
Corynebacterium diphtheriae: Treatment and Prevention
- Treatment = passive therapy with horse anti-toxin
- Antibiotics eradicate organism
- Prevention= immunize with toxoid
