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Infectious Disease Microbiology & Immunology Intermediate
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Catalase-Positive Pathogens

P
L
A
C
E
S
S
Pathogens capable of decomposing hydrogen peroxide (H2O2), predisposing patients with Chronic Granulomatous Disease (CGD) to recurrent infections.

Catalase degrades hydrogen peroxide into water and oxygen. In Chronic Granulomatous Disease (NADPH oxidase deficiency), phagocytes cannot generate endogenous H2O2; catalase-negative organisms provide their own H2O2 which neutrophils can utilize, but catalase-positive bugs destroy it.

Systematic Breakdown

P

Pseudomonas aeruginosa

Opportunistic Gram-negative bacillus causing ecthyma gangrenosum and pneumonia in CGD and neutropenia.

L

Listeria monocytogenes

Facultative intracellular Gram-positive rod with tumbling motility; unpasteurized milk and cold cuts.

A

Aspergillus fumigatus

Monomorphic fungus with 45-degree acute-angle branching hyphae; leading cause of death in CGD patients.

C

Candida albicans

Dimorphic yeast producing pseudohyphae; causes recurrent mucocutaneous and invasive candidiasis.

E

Escherichia coli

Lactose-fermenting Gram-negative rod causing recurrent UTIs and sepsis.

S

Staphylococcus aureus

Coagulase-positive staph causing recurrent suppurative skin abscesses and osteomyelitis in CGD.

S

Serratia marcescens

Slow lactose fermenter producing red pigment; osteomyelitis and lymphadenitis in CGD.

High-Yield Clinical Pearls & Exam Tips
  • Patients with Chronic Granulomatous Disease (X-linked mutation in gp91phox of NADPH oxidase) suffer recurrent infections specifically by these organisms.
  • Diagnostic test for CGD: Dihydrorhodamine (DHR) flow cytometry assay (absence of green fluorescence) or Nitroblue Tetrazolium (NBT) reduction test (remains yellow/colorless).
Related Pharmaceuticals
Trimethoprim-Sulfamethoxazole (prophylaxis) Itraconazole Interferon-gamma
Related Clinical Conditions
Chronic Granulomatous Disease Invasive Aspergillosis Staphylococcal Abscess
Authoritative Sources: Robbins & Cotran Pathologic Basis of Disease 10e · First Aid USMLE Step 1

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System Notice

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