is a cosmopolitan
filamentous fungus that thrives in soil and decomposing fruit and
vegetable matter. Rhizomucor species are often isolated from
composting or fermenting organic matter and they are also rare agents of
serious to fatal infections in humans. Except for Rhizomucor
variabilis, Rhizomucor species are
thermophilic in nature and
can grow at temperatures as high as
Rhizomucor contains three species namely, Rhizomucor pusillus,
Rhizomucor miehei, and Rhizomucor variabilis. Rhizomucor
variabilis is very close to Mucor hiemalis phylogenetically.
Maximum growth temperature, biochemical assimilation profile, thiamine
dependency, and the diameter of the sporangia are the characteristics that
aid in the differentiation of the three Rhizomucor species from
each other. Rhizomucor miehei is homothallic while Rhizomucor
pusillus is either homo - or heterothallic.
Pathogenicity and Health Effects
occasional agents of angio – invasive disease referred to as
which is often considered as fatal. The most frustrating features of this
disease are vascular invasion that causes necrosis of the infected tissue,
and perineural invasion. Rhizomucor pusillus is seldom an agent of
cutaneous, pulmonary, rhinofacial, and disseminated zygomycosis especially
infecting neutropenic patients with hematological malignancies and
diabetes mellitus. Otherwise healthy individuals have been reported with
cutaneous infections caused by Rhizomucor variabilis. Aside from
human infections, animal infections are common as well such as bovine
mycotic abortion due to Rhizomucor species.
Growth rate is very rapid and colonies are typically cotton – candy like
surface colony color is initially white becoming gray to yellowish brown
in time while reverse is white to pale; and
species other than Rhizomucor variabilis are thermophilic and yield
optimum growth at temperatures as high as 54°C.
– septate or scarcely septate broad
sporangiospores are present;
Rudimentary rhizoids are located on stolons between the sporangiophores
but are often rare or difficult to recognize;
Sporangiophores are irregularly branched, with branches sometimes arranged
in an umbel at the apex;
Sporangia are brown in color, round - shaped, with well – developed
columella, and with diameter ranging from 40 – 80 µm;
Sporangiospores are small, round or oval in shape, unicellular, and with
diameter ranging from 3 – 4 µm;
Apophysis is absent;
present, zygospores are formed in the aerial hyphae, round to slightly
compressed, and dark brown to blackish in color;
microscopic morphology of Rhizomucor appears to be intermediate
between that of Rhizopus and Mucor;
species differ from Mucor by having the ability to grow at 50 -
55°C and by having rhizoids and stolons;
by having branched sporangiophores and rhizoids not arising opposite the
Absidia by having globose sporangia and sporangiophores that are
not swollen where they join together with the columellae.
precautions are required, no special safety measures needed.
susceptibility data are not available for Rhizomucor species.
Rhizomucor infections includes antifungal and surgical therapy, which
is also similar to the treatment of zygomycosis caused by fungi belonging
to class Zygomycetes. For antifungal treatment, amphotericin B is most
commonly used such as liposomal amphotericin B. Early diagnosis and
treatment are vital and mortality rate is high.