Zygomycetes

Zygomycetes

Fast growing fungi, present in the environment (saprophytic). Mostly ASEPTATE (coenocytic) hyphae (many nuclei/cells), SEXUAL reproduction through ZYGOSPORES, uncommon isolate in labs...presence means contamination or devastating zygomycosis in immunocompromised

Mucormycosis/Zygomycosis

Rare, severe, and fatal opportunistic infection that affects immunocompromised, broad spec antibiotics, breakdown of cutaneous barrier, burns, etc.

Mucormycosis/zygomycosis: infection process

1. Inhaled spores trapped in sinuses or reach distal airspace
2. Replication of spores occurs (usually macrophages and white blood cells would block replication... neutropenia, corticosteroid, etc. cannot)
3. Undetected fungal proliferation, angioinvasion (invasion of blood vessels), and necrosis
4. Progressing fungal invasion, hemorrhage, and necrosis
5. Extensive necrosis limits drug delivery and immune response
6. Dissemination

Types of Mucormycosis/Zygomycosis

Rhinocerebral: Starts in sinus and spreads to brain, most common in uncontrolled diabetes

Pulmonary: inhalation of fungal spores

GI: Ingestion of the fungal spores; more common in infants

Mucormycosis/Zygomycosis: Specimen processing

Skin scrapings, sputum, and exudates examined by KOH preparation

Mucormycosis/Zygomycosis Microscopic Features

Aseptate broad ribbon-like hyphae with right-angle branching of conidiophores

Fungal Structures of Mucormycosis/Zygomycosis

*Appearance in culture, not specimens in tissue*

Columnella: sterile, dome-like structure at tip of sporangiophore

Apophysis: funnel-shaped swelling of sporangiophore, immediately below columnella (unique to and only seen in SOME zygomycetes)

Sporangiophore: specialized hyphae that bears a sporangium

Sporangium: sac-like structure producing asexual spores endogenously by cytoplasmic cleavage

Stolon: a running hyphae from which rhizoids and sporangiophores arise

Rhizopus: Basic Info

Grows best at 45 degrees, sexual reproduction through zygospores , asexual reproduction through sporangium

Rhizopus: microscopic

Large , irregular aseptate hyphae (in vivo only you will see right angle branching hyphae)

Rhizoids (root-like hyphae)

Spherical sporangium

Columnella is spherical to elongated

Brown and unbranched sporangiophores

Non-prominent apophysis

Zygospores

Mucor: Basic Info

Found in soil, decaying fruits and vegetables

Infections found in humans, amphibians, cattle, and swine

Most grow at less than 37 degree C, but some are infectious to humans and are thermo-tolerant

Mucor: Microscopic

Broad, aseptate/barely hyphae

No rhizoid hyphae

No apophysis or stolon

Round sporangium with round-oval sporangiospores

Sporangiophore are hyaline and can be branched or unbranched

Zygospores

Rhizomucor: Microscopic

*Has similar characteristics to rhizopus and mucor*

Aseptate or sparsely septate, broad hyphae

Rudimentary rhizoids located on stolons between sporangiophores

Brown and round Sporangium

No apophysis

Stolon present

Columnella are prominent and spherical to pyriform in shape

Sporangiospores are small and round to ellipsoidal

Irregularly branched sporangiophores

Zygospores, if present, round to slightly compressed and dark brown to blackish brown

Absidia/Lichtheimia: Microscopic

Pyriform sporangium

Rhizoid hyphae between sporangiophores

Contain septa just below sporangium in the sporangiophore

Branching sporangiophores arise in groups of 2-5 at internodes

Sporangiophore widens at funnel-shaped apophysis

Conically-shaped columnella

Cunninghamella: Characeristics

Found in soil and plant material, especially in Mediterranean and subtropical zones (not in temperature climates)

In addition to being OPPORTUNISTIC, it is a common lab contaminant

Cunninghamella: Microscopic

Does not contain a sporangium, but rather terminal vesicles with SPORANGIOSLES that contain spherical sporangiospores

Sporangiosles often have needle-like projections

Sporangiophores erect and form short, lateral branches

Swollen terminal vesicle instead of sporangium with spine-like denticles... these terminal vesicles contain the sporangiosles

Five Zygomycetes Microscopic Overview

Rhizopus: have rhizoids; sporangium are round and pigmented and base is located at rhizoids

Mucor: no rhizoids, not pigmented, sporangiophore can branch irregularly

Rhizomucor: less developed rhizoids, rhizoids are not at base of sporangiophores, sporangiophores can branch

Absidia: pear-shape/pyriform sporangium, septum just below sporangium, well developed apophysis, sporangiophores arise between rhizoids

Cunninghamella: hyaline hyphae, erect sporangiophores that form lateral branches, swollen terminal vesicles at end of sporangiophore that contain sporangiosles projections that contain sporangiospores