High-Yield Infectious Disease Information – USMLE Step 2 CK Exam

by / Wednesday, 07 July 2010 / Published in Internal Medicine

Gram Stain Characteristics

ORGANISM CHARACTERISTICS STAINING CHARACTERISTICS
Gram (+) organisms Blue in color
Gram (-) organisms Red in color
Gram (+) cocci (pairs) S. Pneumonia
Gram (+) cocci (chains) Streptococcus
Gram (+) cocci (clusters) Staphylococcus
Gram (-) diplococci Neisseria
Gram (-) rods Hemophilus
Gram (-) rods with mucoid capsule Klebsiella
Pseudohyphae on stain Candida
Acid Fast Organisms Mycobacterium, Nocardia
Silver Staining Pneumocystis Carinii
Spirochete Borrelia, Treponema/Leptospira(darkfield)

Common situations and their associated organisms

SITUATION ASSOCIATED ORGANISMS
Cellulitis from a dog or cat bite Pasteurella Multocida
Burn wound infection with a blue/green color Pseudomonas
Baby Paralyzed after eating honey Clostridium Botulinum
Diarrhea after taking antibiotics Clostridium Difficile
Pricked by thorn while gardening Sporothrix Schenckii
Gastroenteritis in young child Rotavirus
Diarrhea after traveling to Mexico E. Coli
Aplastic crisis in Sickle Cell patient Parvovirus B19
Food poisoning after eating reheat rice B. Cereus
Food poisoning after eating raw seafood Vibrio Parahemolyticus
Pneumonia in Southwest USA Coccidioides Immitis
Pneumonia after exploring caves Histoplasma Capsulatum
Pneumonia after exposure to bird droppings in Ohio Histoplasma Capsulatum
Pneumonia after exposure to exotic birds Chlamydia Psittaci
Pneumonia in a patient with silicosis Tuberculosis
Diarrhea after hiking or drinking from a stream Giardia Lamblia
B12 deficiency Diphyllobothrium Latum
Fever and muscle pains after eating raw meat Trichinella Spiralis
Pneumonia after being near an air conditioner or water tower Legionella Pneumophilia
Slaughterhouse worker with a fever Brucellosis
Fungal ball/hemoptysis after TB or cavitary lung disease Aspergillus

High-yield conditions/illnesses and their most likely organism and treatments

CONDITION/ILLNESS ORGANISM BEST TREATMENT
Cellulitis Staph, Strep Antistaphylococcus penicillin
UTI E. Coli TMP-SMX, Nitrofurantoin (in pregnancy)
Endocarditis Staph, Strep Antistaphylococcus, Aminoglycoside
Sepsis Gram (-) organisms 3rd generation cephalosporin’s
Septic Arthritis Staph Aureus Antistaphylococcus PCN, Vancomycin (severe)
Meningitis (neonatal) Group B Strep, E. Coli, or Listeria Ampicillin + Aminoglycoside
Meningitis (child – adult) Neisseria Meningitidis 3rd generation cephalosporin
Osteomyelitis Staph Aureus, Salmonella (Sickle cell patient) Antistaphylococcus PCN, Vancomycin
Pneumonia Strep Pneumonia, H. Influenza 3rd generation cephalosporin
Pneumonia (atypical) Mycoplasma, Chlamydia Doxycycline, Macrolide
Bronchitis H. Influenza Amoxicillin, Erythromycin

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