In this article we will discuss about the types and characteristics of phycomycoses.
The phycomycoses have several synonyms such as mucormycoses, entomophthoromycoses, oomycoses, etc. The phycomycoses are caused by such fungi that had been previously grouped in the class Phycomycetes.
Recently, the fungi classified under Phycomycetes have been put under two sub-divisions Mastigomycotina (with two classes Oomycetes and Chytridiomycetes) and Zygomycotina (with two classes Zygomycetes and Trichomycetes).
Clark (1968) proposed the name mucormycoses for those mycoses caused by the members of the order Mucorales, and entomophthoromycoses for those mycoses caused by the fungi of the order Entomophthorales.
The phycomycoses are the fatal disease of man and animals in whom the vital organs are infected by the species of Absidia, Mucor and Rhizopus. Mycoses caused by Absidia, Mucor, Rhizopus and Cunninghamella (Table 24.3) occur usually in diabetic patients. In rabbits which have been made diabetic with alloxan, cerebral and pulmonary phycomycoses have been produced with Rhizopus oryzae and R. arrhizus.
The characteristic features of mycoses are the invasion and growth in nasal mucosa and the underlying tissue followed by rapid destruction of tissue. In severe cases the hyphae extend to brain and invade the blood vessels.
Clinical Types of Phycomycoses:
Some of the following clinical types are discussed below:
1. Phycomycosis of Orbital and Central Nervous System:
The pathogens infect the para-nasal sinuses and spread in nasal mucosa and underlying tissues. It is followed by rapid disintegration of tissue resulting in severe cellulitis to the area of orbital. In severe cases even patients dies between 2 and 10 days. If the mycelia continue to grow at the same speed these may penetrate the lungs. Predisposing factor for establishment of mucormycosis may be the diabetic acidosis.
2. Disseminated Mucormycosis:
In addition to the above infection sites, pulmonary lesions, gastrointestinal ulcers and other example of dissemination may also take place. Cunninghamella elegans is the etiologic agent of pulmonary infection. Some members of mucorales may cause abortion in cattle’s as well.
Table 24.2 : Mushroom toxins.
3. Skin Ulcer:
Mortierella spp. are associated with dermal ulcers. In deep subcutaneous areas a few fragements of coenocytic hyphae can be observed.
4. Entomophthoromycosis:
Entomophthoromycosis is of two types on the basis of causal organism. Basidiobolus ranarum causes the disease, entomophthoromycosis basidiobolae, whereas the mycosis caused by Conidiobolus coronatus is known as entomophthoromycosis conidiobolae.
Lie-Kian-Joe (1956) reported three cases of mycotic infection by B. ranarum from Indonesia. B. ranarum infects subcutaneous tissues and muscle fascia. It spreads quickly over neck, arms and upper chest. It could be soon healed up without any treatments. However, some other cases were reported involving additional areas where no natural healing could be observed.
The lesions developed seem firm, lens shaped and sharply demarcated. The demarcated lesions could be lifted from muscle fascia after insertion of fingers in a fold of skin under the edge of lesion. Moreover, the skin becomes hyper-pigmented or discoloured. Infection by the pathogen occurs either through insect bites or piercing of contaminated thorns into the epidermal layer.
Entomphthoromycosis conidiobolae (= phycomycosis entomophthorae) is caused by E.coronatus in man and horses. The mycosis could be observed as nasal polyps and large granulomas of nasal cavity. Lesions begin first in the inferior turbinate thereafter, spread in submucosa, sutures and Para nasal sinuses.
Finally, the subcutaneous tissues of the face is covered. Moreover, the lesions spread beneath the facial muscles and widely covers the face. The patients feel discomfort from swollen tissue on the face but not pain. Clark (1968) studied this disease in Nigerians and found that the ratio of male and female was 10: 1.
Culture Characteristics of Phycomycoses:
1. Absidia Corymbifera:
It grows rapidly and covers the Petri plates within a few days. Colony is grey, wooly; mycelium coenocytic with numerous sporangiophores of a few millimeters in length emerging upwardly from the intermodal portions on the stolon (Fig.24.6) and freely branched. Sporangiophores possess rhizoids. Sporangiophores branch to form corymbs and terminate to form sporangia of 0-70 µm diameter with a columella. Spores are spherical to oval, 2-3×3-4 µm in size.
2. Rhizopus:
Species of Rhizopus produce simple but branched sporangiophores in some species. Sporangiophores develop individually or in groups from rhizoids. The adjacent rhizoids and sporangiophores are interconnected by stolons.
Sporangiophores arise at the nodes i.e. directly above the rhizoids (Fig. 24.10). R. oryzae, which is used in making a fermented food (Koji) in Japan, is pathogenic also. It infects the patients suffering from diabetes mellitus. R. arrhizus arises from the swollen segments of hyphae. These two species are the most frequent pathogens in men. In addition, R. cohnii, R. microsporus and R. equinus have been isolated from mycotic abortions in animals.
3. Mucor:
Mucor produces grey mycelium on the nutrient medium. Mucor possesses simple or branched sporangiophores that come out from the surface of substratum. Neither stolons nor rhizoids are formed by this fungus.
Sporangia are produced on sporangiophores which are large sized (Fig. 24.11). Sporangium consists of a columella in the centre. Spores are spherical and smooth walled. The pathogenic species in men are M. ramosissimus, M. pusillus, M. racemosus, etc.
4. Basidiobolus Haptosporus:
It causes entomophthoromycosis basidiobolae in Indonesia, tropical Africa and Southern Asia. The etiologic agent was identified as B. ranaum in some text. Srinivasan and Thirumulachar (1967) concluded its correct name as B. haptosporus. On the Sabouraud’s agar it forms a grey to yellowish, thin, flat, glabrous and radially folded colony.
Hyphae are 8 to 20 µm in diameter with occasional septa which become very numerous with the production of spores. Surface of the colony becomes covered within white bloom composed of very short aerial hyphae, sporangia, chlamydospores and zygospores. Sporangiospores are 30-50 µm in diameter.
5. Candidiobollus Coronatus (syn.. Entomophthora Coronata):
It grows rapidly on all common media. At first colonies are globose, abundant, short aerial. Conidia are globose and multinucleate. Conidia are capable of replicating. The hyphae are produced as the colony matures.
In C. coronatus no sporangia are formed but the conidia (10-20 µm diameters) are produced on hyphae which are forcibly discharged from the tip of conidiophores. Hyphae produce a short conidiophore at the tip of which a secondary conidium is borne. This process of replication continues until the nutrients are exhausted.