Source / episode info

• **Episode:**623
• **Title:**DIP Ep 623: Last Minute Microbiology Review (Step 2 and 3)
• **Published:**2025-09-15
• Source:Episode page

One-liner

This episode provides a comprehensive review of high-yield infectious disease topics, covering osteomyelitis (Staph aureus), community-acquired pneumonia pathogens (S. pneumoniae, Legionella), meningitis etiologies and prophylaxis (Meningococcus, Listeria), fungal infections (Candida, Cryptococcus, Aspergillus), and key antibiotic mechanisms/resistances (Vancomycin, Linezolid).

High-yield summary

• Osteomyelitis: The most common cause is Staphylococcus aureus, especially following recent surgery or trauma. In sickle cell disease patients, always consider Salmonella first; if not listed, use S. aureus.
• CAP/Pneumonia: Streptococcus pneumoniae remains the most common adult CAP pathogen. For neonates (first 20 days of life), Group B Streptococcus is the most common cause of sepsis and meningitis.
• Meningitis Prophylaxis: In close quarters (military, dorms, ships), suspect Neisseria meningitidis. Empirical prophylaxis is preferred: Rifampin > Ceftriaxone > Ciprofloxacin.
• Legionella Pneumonia: Associated with HVAC systems and plumbing work; presents as interstitial pneumonia, diarrhea, and hyponatremia due to impaired renin/aldosterone axis function. Diagnosis relies on the urinary antigen test.
• Fungal Infections: Candida infections are common in immunocompromised patients (e.g., those on inhaled steroids). Disseminated candidiasis is best treated with an Echinocandin (Caspofungin, Micafungin, Anidulafungin).
• TB/Cavity Lesions: When evaluating cavitary lung lesions, consider Mycobacterium tuberculosis (especially in immunocompromised patients), Aspergillus, Squamous Cell Carcinoma, and post-viral pneumonia.

Learning objectives

• Identify the most likely pathogen causing osteomyelitis in specific risk groups (e.g., trauma, sickle cell).
• Differentiate between common causes of pneumonia based on patient history and lab findings (e.g., Legionella vs. S. pneumoniae).
• Recall appropriate empirical antibiotic prophylaxis for meningitis in close quarters or neonates.
• Master the differential diagnosis and treatment principles for various fungal infections (Candida, Cryptococcus, Aspergillus).
• Understand the mechanism of action and clinical implications of key antibiotics (e.g., Linezolid, Vancomycin resistance, Amphotericin B nephrotoxicity).