Bacteria and Fungi

Polysaccharide Encapuslated Organisms

Organism Metabolic Characteristics

  • Lactose Fermenting Gram-Negative Rod
  • Non-Lactose Fermenting Gram-Negative Rod
  • Non-Fermenting Gram-Negative Rod

Moraxella Catarrhalis (see Moraxella Catarrhalis, [[Moraxella Catarrhalis]])

  • Path: Gram-negative intracellular cocci


  • Anaerobe


  • Anaerobe

Rhodococcus Equi (see Rhodococcus Equi, [[Rhodococcus Equi]])

  • Path: Gram-positive coccus or bacillus
    • May stain weakly acid-fast

Bacillus Anthracis/Listeria Monocytogenes

  • Path: Gram-positive rod


  • Path: long, branching, Gram-positive filamentous rods (0.5 to 1.5 µm in diameter)
    • May stain weakly acid-fast


  • Path: Gram-positive diphtheroidal or filamentous branching rods

Mucor (Zygomycetes)

  • Path: large (10-15 µm) broad 90° angle branching non-septate hyphae
    • Only rare side branches
    • No pseudohyphae or budding yeasts
    • Stain better with H+E than with fungal stains
  • Rx: Posaconazole (not FDA released yet) or Ampho


  • Rx: Vori or Ampho


  • Rx: Vori

Aspergillus (see Aspergillus, [[Aspergillus]])

  • Monomophic fungus
  • Path: 45 degree angle branching
  • Rx: Vori (superior to Ampho for invasive aspergillus)


  • 50% of infections are due to non-albicans species
  • Rx-Candida albicans: Caspo or Mica
  • Rx-Candida krusei: as many as 95% of Candida krusei isolates are Flucon-resistant, so Ampho B is indicated


  • Dimorphic fungus (mycelial phase at RT and yeast phase at body temperature)
  • Path: no characteristic morphologic features

Coccidioides Immitis (see Coccidioidomycosis, [[Coccidioidomycosis]])

  • Dimorphic fungus (mycelial phase at RT and yeast phase at body temperature)
  • Path: spherules


  • Dimorphic fungus (mycelial phase at RT and yeast phase at body temperature)
  • Path:


  • Path: large organism (8-20 µm) with thick double-refractile cell wall/single-budding with broad base of attachment (”broad-based buds”)/multiple nuclei
    • 10% KOH exam: easiest technique to identify organism
    • Other fungal stains (PAS, calcofluor white, silver stain): more sensitive, especially when used in combination
    • PAP Stain: also sensitive (In one study, sputum were 78% positive by PAP, compared to 37% positive by KOH + PAS)


  • Monomophic fungus
  • Path: forms vary in size, ranging from 2 to 15 µm with average diameters of 4 to 7 µm.
    • Yeast organisms have a thick mucinous capsule, which appears as clear halo in Grocott-Gomori methenamine silver staining