RHS13 - Respiratory Tract Infections 4

Question 1

What are the two Gram Negative diplococci we need to know?

Answer 1

Neisseria spp. (gonorrhea and mengitidis)

Moraxella catarrhalis

Question 2

What is the identifying lab information for Moraxella catarrhalis and how is it differentiated from Neisseria spp.?

Answer 2

• Gram Negative diplococcus
• Oxidase positive (they produce CytC oxidase) and Aerobic
• Usually resistant to penicillins
• Round opaque colonies will grow on both blood and chocolate agar and they turn pinkish after 48hrs. They also demonstrate the “hockey puck sign” which means the colonies will slide around the agar if pressed on with a probe.
• Can be differentiated from Neisseria by testing for the presence of DNAse and nitrate reduction. Neisseria exhibits neither of these

Question 3

What are the clinical features of Moraxella catarrhalis?

Answer 3

• Primarily colonize the URT in children or adults with comorbidities (COPD)
• Often causes otitis media in children
• Can cause acute exacerbation of COPD in elderly
• Can cause sinusitis

Question 4

Describe the pathogenesis of a Moraxella catarrhalis infection

Answer 4

1. Harmless colonization of nasopharynx
2. Another infection (usually viral) creates an optimal environment for migration and M. catarrhalis moves from the nasopharynx to the middle ear through the eustachian tube or down into the LRT
3. Mechanism isn’t understood but the acute exacerbation of COPD seems to only occur when several strains of M. catarrhalis have been acquired

Question 5

Answer 5

D