Two forms of Coccidioides

• 25-yo African-American man presents with fever, nonproductive cough, skin lesion. sick for a month

• temperature 102^o F, diffuse rales, patchy infiltrates on CXR

• wart-like lesions on his back that shows round structures with internal structures inside them, termed spherules. this is the tissue form of Coccidioides

• histology: caseation surrounding spherules and large endospores coming out of a spherule. indeed, endospores are the internal structures of the spherules

• in soil, forms conidia within the mycelium, not externally like most other fungi

• when these are broken up and inhaled, they begin to round up (forming a spherule) and divide internally until they are full off endospores and release them (~96 hours after inhalation)

SEM and TEM of arthroconidia of Coccidioides

• these mycelia contain arthroconidia, which are fungal spores produced by segmentation of pre-existing hyphae (Wikipedia)

• every other cell in the hyphae is an empty cell that can be broken by wind to form one infectious particle

• then, these round up and form spherules after inhalation

Micrograph

• internal division inside the spherule occurs; the endospores get smaller and smaller until the spherule ruptures and pours them all out

• each endospore has the capacity to grow into a completely mature spherule or, if coughed up, to form more mycelia in the soil

• so it can go either way, and what makes the decision is the environment

Category: Microbiology Notes