Microbiology for USMLE
Free microbiology gallery for Step 1 and Step 2 CK. Every high-yield bacterium, virus, fungus, and parasite with the buzzword presentations, associated diseases, and first-line treatments boards actually test.
BACTERIA · 15FUNGUS · 4PARASITE · 3VIRUS · 3
BACTERIA
Spirochete
Borrelia burgdorferi
Borrelia burgdorferi — Dark-field microscopy
Ixodes tickerythema migrans / bull's-eye rashBell palsy
Gram-positive spore-forming anaerobic rod
Clostridioides (Clostridium) difficile
Clostridioides difficile — Gram stain
pseudomembranous colitistoxins A and Bantibiotic-associated diarrhea
Gram-negative rods (Enterobacteriaceae)
Escherichia coli
Escherichia coli — Gram stain
lactose fermenterpink on MacConkeymetallic green sheen on EMB
Gram-negative coccobacillus
Haemophilus influenzae
Haemophilus influenzae — Gram stain
chocolate agarfactors V (NAD+) and X (hematin)satellite phenomenon
Gram-negative curved/spiral rod
Helicobacter pylori
Helicobacter pylori — Gastric biopsy (Giemsa stain)
urease-positivecurved gram-negative rodduodenal ulcer
Gram-positive rod (facultative intracellular)
Listeria monocytogenes
Listeria monocytogenes — Gram stain
tumbling motility at 22°Cactin rocketscold enrichment
Acid-fast bacillus (obligate intracellular)
Mycobacterium leprae
Mycobacterium leprae — Acid-fast skin biopsy
acid-fastcooler body temperaturearmadillos
Acid-fast bacillus (mycolic acid cell wall)
Mycobacterium tuberculosis
Mycobacterium tuberculosis — Ziehl-Neelsen acid-fast stain
acid-fast bacillicord factorcaseating granuloma
Gram-negative diplococci
Neisseria meningitidis
Neisseria meningitidis — Gram stain of CSF
intracellular gram-negative diplococcikidney-bean shapedpetechiae/purpura
Gram-positive filamentous, partially acid-fast
Nocardia spp.
Nocardia — Modified Ziehl-Neelsen (weakly acid-fast)
partially acid-fastbranching filamentssoil aerobe
Gram-negative rod (non-fermenter)
Pseudomonas aeruginosa
Pseudomonas aeruginosa — Pigment production on culture
blue-green pigmentgrape/fruity odorburn wounds
Gram-positive cocci
Staphylococcus aureus
Staphylococcus aureus — Gram stain (grape-like clusters)
grape-like clustersgolden coloniescoagulase-positive
Gram-positive cocci
Streptococcus pneumoniae
Streptococcus pneumoniae — Gram stain
rusty sputumlancet diplococcioptochin-sensitive
Gram-positive cocci
Streptococcus pyogenes (Group A Strep)
Streptococcus pyogenes — Gram stain (chains)
chains of coccibeta-hemolyticbacitracin-sensitive
Spirochete
Treponema pallidum
Treponema pallidum — Microscopy (syphilis spirochete)
corkscrew motilitypainless chancresnail-track ulcers
FUNGUS
Mold (monomorphic)
Aspergillus fumigatus
Aspergillus — Conidiophore microscopy (septate hyphae 45° branching)
septate hyphae45° branchingfungus ball / aspergilloma
Yeast (dimorphic)
Candida albicans
Candida albicans — Gram stain (yeast + pseudohyphae)
pseudohyphaegerm tube at 37°Cthrush
Encapsulated yeast
Cryptococcus neoformans
Cryptococcus neoformans — India ink preparation
India ink halosoap-bubble lesionsnarrow-based budding
Atypical fungus (extracellular)
Pneumocystis jirovecii
Pneumocystis jirovecii — Toluidine blue / silver stain (cup-shaped cysts)
cup-shaped cystsground-glass infiltratesAIDS CD4 < 200
PARASITE
Flagellated protozoan
Giardia lamblia (G. duodenalis / intestinalis)
Giardia lamblia — Trophozoite microscopy
owl-face trophozoitefatty foul-smelling diarrheacampers/hikers
Apicomplexan protozoan
Plasmodium falciparum
Plasmodium falciparum — Thin blood smear (ring forms)
banana gametocytessignet-ring trophozoitesirregular fevers (malignant tertian)
Hemoflagellate protozoan
Trypanosoma cruzi
Trypanosoma cruzi — Blood smear (trypomastigote)
reduviid (kissing) bugRomaña signmegacolon and megaesophagus
VIRUS
Enveloped dsDNA herpesvirus (β-herpesvirus)
Cytomegalovirus (HHV-5)
Cytomegalovirus — Owl's-eye intranuclear inclusion
owl's-eye inclusioncytomegalic cellheterophile-negative mononucleosis
Enveloped dsDNA herpesvirus (α-herpesvirus)
Herpes Simplex Virus (HSV-1/HSV-2)
Herpes Simplex Virus — Tzanck smear (multinucleated giant cells)
multinucleated giant cellsCowdry A inclusionsmolded nuclei
Enveloped ssRNA retrovirus (diploid)
Human Immunodeficiency Virus 1
HIV-1 — Transmission electron micrograph
CD4 + CXCR4/CCR5reverse transcriptasep24 antigen
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