RHIZOPUS

SPECIES

MICROSCOPIC APPEARANCE

Hyphae broad, not or scarcely septate; rhizoids and stolons present; sporangiophores brown, solitary or in tufts on the stolons, diverging from the point at which the rhizoids form; sporangia rather round; apophysis absent or scarcely apparent; sporangiophores ovoid.

MACROSCOPIC APPEARANCE

Surface: Texture deeply cottony; White becoming gray-brown on surface.
Reverse: Pale white.
Growth Rate: Very rapid growth.

DISTINGUISHING FEATURES

Rhizopus is recognized by the presence of well developed rhizoids situated at the point where sporangiophores are attached to the stolons. In contrast to Mucor , Rhizomucor and Absidia , the sporangiophores are often unbranched and grouped in tufts.

Organism Pathogenic Maximum Growth Temperature Rhizoid Length
(um)
Sporaniophore
Length
(um)

Sporangium
Length
(um)

Columellae Sporangio-
spores
R.
microsporus
Positive 50-52°C 100-120 200-1000 40-130 Slightly elongated;
distinct apophysis
Equal size, average length 4-6um; smooth to slightly striated; almost round to slightly elongated
R.
oryzae
Postive 40-46°C 150-300 500-3500 50-250 Almost round Variable size, average length 6-8um; striated; elongated to lemon-shaped
R.
stolonifer
Negative 30-32°C 300-350 1500-4000 150-350 Almost round Variable in size, average length 9-11um; very striated; elongated to polyhedric

Pathogenic strains grow better at 35 degrees C. than saprophytes.

HABITAT

Rhizopus are cosmopolitan, frequently isolated from soil and agricultural products (cereal, vegetables, etc.). Certain species are plant pathogens.

PATHOGENICITY

Rhizopus is the principal agent of mucormycosis (formally zygomycosis). This rapidly progressing infection is characterized by the cerosis of tissues and the production of infarcts in the brain, the lungs, and the intestines. Primarily, it is patients suffering from diabetic ketoacidosis, malnutrition, severe burns, or immunocompromising conditions who are most at risk to develop this type of infection.

RECOMMENDED MEDIA

INCUBATION

Temperature: 25 degrees C.
Time: 2-7 days.

REFERENCES

1. Hensyl, William R. et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

2. St. Germain, Guy and Summerbell, Richard, Ph.D. 1996. Identifying Filamentous Fungi , 1st ed. Star Publishing Company, Belmont, CA.

3. Larone, Davise, H. 1995. Medically Important Fungi , A Guide to Identification . 3rd ed. American Society for Microbiology Press, Washington, D.C.

4. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.


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