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
Propionibacterium
Peptostreptococcus
Rhodococcus Equi (see Rhodococcus Equi, [[Rhodococcus Equi]])
- Path: Gram-positive coccus or bacillus
- May stain weakly acid-fast
Bacillus Anthracis/Listeria Monocytogenes
Nocardia
- Path: long, branching, Gram-positive filamentous rods (0.5 to 1.5 µm in diameter)
- May stain weakly acid-fast
Actinomyces
- 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
Fusarium
Scedosporium
Aspergillus (see Aspergillus, [[Aspergillus]])
- Monomophic fungus
- Path: 45 degree angle branching
- Rx: Vori (superior to Ampho for invasive aspergillus)
Candida
- 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
Histoplasma
- 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
Paracocci
- Dimorphic fungus (mycelial phase at RT and yeast phase at body temperature)
- Path:
Blastomyces
- 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)
Cryptococcus
- 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