Gram Positive: Corynebacterium & Listeria (non-spore forming rods)

Question 1

General features of Corynebacterium and Listeria. What are the major species of each?

Answer 1

• these are Gram positive rods
• they are NOT spore forming (differentiate between the spore-forming rods Bacillus and Clostridium)
• they mainly affect children and immunocompromised patients
• both are facultative anaerobes
• C. diphtheriae, C. equi, L. monocytogoenes

Question 2

What does Corynebcaterium diphtheriae cause? What’s the pathogenesis?

Answer 2

• causes diphtheria by colonizing the pharynx (forms grey pseudomembranes) where it then releases powerful exotoxins into the bloodstream
• the exotoxins inhibit protein synthesis and mainly target heart and neural cells

Question 3

How do patients with diphtheria usually present? How do we treat it?

Answer 3

• patients are usually children who present with a sore throat, fever, and an inflammatory exudate of the pharynx (the grey pseudomembranes of C. diphtheriae; don’t scrape it off as this will promote exotoxin release into bloodstream!)
• treat with antitoxin, penicillin or erythromycin, and the DPT vaccine

Question 4

How do we culture Corynebacterium diphtheriae?

Answer 4

• culture on potassium tellurite agar and Loeffler’s coagulated blood serum media

Question 5

What does Corynebacterium equi cause? What does this disease resemble?

Answer 5

• causes a necrotizing pneumonia when inhaled by immunocompromized patients
• it is very similar to and resembles tuberculosis via Mycobacterium

Question 6

What are the virulence factors of Listeria monocytogenes? What disease does it mainly cause? How about in pregnant women? How do we treat it?

Answer 6

• flagellated, can grow at cold temperatures, and has listeriolysin O (allows it to escape phagolysosomal destruction)
• causes disease in neonates, pregnant women, elderly, and immunocompromised patients via consumption of contaminated foods (milk, soft cheeses, cold cuts)
• largely causes meningitis (but in pregnant women, it actually causes sepsis)
• treat when suspected by adding ampicillin or trimethoprim-sulfamethoxazole to the empirical regimen

Question 7

Which organisms are the main causes of neonatal meningitis?

Answer 7

• Listeria monocytogenes, Group B Strep (Streptococcus agalactiae), and Escherichia coli