Lecture 4 - Respiratory Tract Infections

Question 1

What are the defence mechanisms of the respiratory tract?

Answer 1

Vibrissae - to physically block particles
Mucus - traps microbes and has lysozyme that digests peptidoglycan
Mucociliary escalator - sweeps foreign bodies up and out of respiratory tract
Sloughing of epithelial cells - removes bacteria
Mucosa-associated lymphoid tissue (MALT) - engulf and kill penetrating bacteria

Question 2

A major bacterial pathogen of the respiratory tract is Haemophilus influenzae type B, what are its growth factors and virulence factors?

Answer 2

G- short rods
Requires both X factor (haemin, haematin) and V factor (minimally NAD) to grow. Grows well in chocolate blood agar

Capsule inhibits phagocytosis and sticks to mucosal lining.
Outer membrane proteins act as adhesins
IgA protease cleaves IgA which is antibody in mucus
Able to squeeze between apical tight junctions including BBB
Lipooligosaccharides and glycopeptides in outer membrane: mimic host cell membrane to hide from IS, also impairs action of cilia and damages respiratory epithelium

Question 3

What are the systemic effects of Hib infection?

Answer 3

Cellulitis - bacterial skin infection, swollen and red
Septicaemia - bacterial infection of bloodstream
Meningitis - fever, fits, bulging fontanelle in infants

Question 4

What are the treatment options for Hib infection?

Answer 4

Treatment must be bactericidal, penetrate lipid membrane, and be lipid soluble

Ampicillin if the particular strain is sensitive
Broad spectrum antibiotics
Possible prophylaxis

Question 5

Which bacteria causes Diphtheria? And what are it’s virulence factors.

Answer 5

Corynebacterium diphtheriae

Corynebacteriophage beta carries tox gene, causes pathogenicity in C. diphtheriae
Encodes A-B toxin which disrupts protein synthesis