Atypical — Flashcards

Flashcard 1: Name the clinical presentation, culture medium, and treatment for Mycoplasma pneumoniae.

Answer: • Clinical: Atypical "walking" pneumonia • Culture: Eaton's agar • Treatment: Macrolides or Fluoroquinolones

Extra: Note: Mycoplasma pneumoniae lacks a cell wall, making it naturally resistant to penicillins and cephalosporins. It is associated with high titers of cold agglutinins (IgM).

Flashcard 2: What are the key associations to remember for cold agglutinin?

Answer: IgM, Mycoplasma, Mononucleosis (EBV)

Flashcard 3: Mycoplasmal pneumonia (Most common cause)

Answer: Which organism is the most common cause of atypical pneumonia (walking pneumonia)?::Mycoplasma pneumoniae (Eaton agent)

Extra: • Features: Insidious onset, headache, nonproductive cough, and diffuse interstitial infiltrates. • Patient profile: Young adults (<30 y/o), military recruits, and prisoners. • Diagnosis: PCR, Cold agglutinins (IgM), culture on Eaton agar. • Treatment: Macrolides (e.g., Azithromycin), Doxycycline, or Fluoroquinolones. • Note: Lacks a cell wall (does not stain on Gram stain; resistant to β-lactams).

Flashcard 4: What factor explains Mycoplasma's inability to Gram stain?

Answer: no cell wall!

Flashcard 5: What is the Gram stain and morphology of Nocardia spp.?

Answer: Gram-positive branching filaments

Extra: Key features of Nocardia: - Aerobe - Weakly acid-fast (modified Ziehl-Neelsen stain) - Found in soil - Clinical: Pneumonia/brain abscess in immunocompromised; cutaneous infections after trauma in immunocompetent. - Treatment: Sulfonamides (e.g., TMP-SMX)

Flashcard 6: tuberculoid leprosy

Answer: Mycobacterium leprae

Extra: few hairless skin plaques6 months of dapsone and rifampin

Flashcard 7: What is the characteristic staining and culture status of Mycobacterium leprae?

Answer: Acid-fast bacillus (AFB) that cannot be cultured in vitro.

Extra: • Disease: Leprosy (Hansen's disease) • Animal reservoir: Armadillos (US) • Growth: Obligate intracellular; prefers cool temperatures (skin, peripheral nerves) • Staining: Weakly acid-fast (modified Ziehl-Neelsen)

Flashcard 8: What are the clinical characteristics of Mycobacterium avium complex (MAC)?

Answer: Acid-fast bacilli; causes disseminated disease in immunocompromised patients (AIDS).

Extra: Prophylaxis/Treatment: Azithromycin or Clarithromycin. Mycobacterium avium-intracellulare complex (MAC).

Flashcard 9: What are the key clinical and microbiological features of Mycobacterium kansasii?

Answer: Photochromogen (Runyon Group I) NTM causing TB-like pulmonary symptoms.

Extra: Mycobacterium kansasii: - Long, thick, cross-barred bacilli. - Acid-fast (Ziehl-Neelsen stain). - Photochromogen: produces yellow-orange pigment when exposed to light. - Clinically mimics pulmonary Tuberculosis (TB). - Treatment: Rifampin, ethambutol, and isoniazid/clarithromycin.

Flashcard 10: Morphology and staining characteristics of Mycobacterium tuberculosis?

Answer: Acid-fast bacilli (AFB) / Gram-positive (weakly)

Extra: Mycobacterium tuberculosis is a slender, slightly curved, obligate aerobic bacillus. Its cell wall is extremely rich in mycolic acids, which prevents Gram staining (stains poorly) and makes it Acid-Fast (resists decolorization by acid-alcohol).