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  #1  
Old 04-03-2011
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Arrow Practice Question, Microbiology #4

A 10 year old boy presents to the emergency department with a mild fever, chest pain, and cough that has been present for the past week. The boy was put on azithromycin by his primary care physician, but the boys symptoms have gotten worse. His mother complains that the boy has had recurrent infections and is small for his age. A neutrophil function test shows lack of NADPH oxidase function. Which of the following is most likely the causative agent for this boy’s symptoms?

A. Streptococcus pneumoniae
B. Mycoplasma pneumoniae
C. Histoplasmosis capsulatum
D. Aspergillus fumigatis
E. Mycobacterium tuberculosis
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Old 04-03-2011
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CGD patient is susceptible to organism with catalase including Staph. aureus, E. coli, Klebsiella spp, Aspergillus spp and Candida spp.

The answer is : D
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Old 04-03-2011
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Correct Answer D is correct!

D is correct!

This is apparently a question that they love to ask on Step 1. We must know the defect in CGD (NAPDH Oxidase def) and the organisms that can cause infection (catalase positive)

Why do catalase positive organisms specifically affect these patients?

Chronic granulomatous disease of childhood is an X-linked recessive disease that is associated with a deficiency of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. This enzyme is necessary to convert molecular oxygen to superoxide free radicals. Superoxide free radicals then are converted by superoxide dismutase to peroxide. MPO combines peroxide with chloride ions to form bleach, which kills phagocytosed bacteria in phagolysosomes. Deficiency of NADPH oxidase leads to a deficiency of peroxide and inability to kill bacteria that are catalase positive, such as
S. aureus. When this pathogen is phagocytosed, the peroxide that normally is produced in its metabolism is immediately degraded by catalase. Patients with chronic granulomatous disease cannot kill S. aureus. Streptococci are catalase negative, however, and when they are phagocytosed, the peroxide that they normally produce is converted to bleach by MPO, and the bacteria are killed.

Aspergillus is the only catalase positive organism listed above
. What are the other catalase positive organisms you ask? Good question, see below:

This was a post by Betro Sadek in 2009:

SPACE
  • Staphylococci (important not confuse it with streptococci)
  • Pseudomonas aeroginosa
  • Aspergillus fumigatus
  • Candida
  • Enterobacteriaceae (specially Klebsiella and Serratia both of which can cause pneumonia and UTI)
Worth to remember that none of the anaerobes are Catalase positive

Also some others are Catalase positive
  • Nisseria (Gonorrhea & Meningitidis)
  • Vibrio
  • Nocardia
  • Campylobacter & Helicobacter
  • Gardnerella vaginalis
  • Pseudomonas cepacia
  • Mycobacterium Tebeculosis also produce a heat sensitive catalase ( active only in body temperature ) so it become catalase negative at 68.0 "F
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  #4  
Old 04-09-2011
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Aspergillosis...

because it is catalase positive...
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