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  • Penicillium: Penicillium is a genus of ascomycetous fungi. It belongs to the ascomycota fungi division. Ascomycota is the largest division of fungi. This genus of fungi is of major importance to man; and they have application in antibiotic production and even in food production. Penicillin is an antibiotic used to treat bacterial infection, and it is naturally sourced from a member of the Penicillium genus known as Penicillium chrysogenum (also known as P. notatum). Penicillium species are recognized by their dense brush-like spore-bearing structures called penicilli (singular: penicillus). Structurally, the conidiophores are simple or branched and are terminated by clusters of flask-shaped phialides. The spores (conidia) are produced in dry chains from the tips of the phialides, with the youngest spore at the base of the chain; and the conidia of Penicillium species usually assume a paint-brush morphological pattern (Figure 1). Penicillium is found in the soil, decaying vegetation, and in the air. They are common contaminants on various substances. Penicillium causes food spoilage, and it colonizes leather objects and other household furniture. It is an indicator organism for dampness indoors. Some Penicillium species are known to produce toxic compounds known as mycotoxins, which have pathological effects on humans. In terms of their reproduction, some species of Penicillium reproduce sexually by means of asci and ascospores produced within small stony stromata. However, Penicillium reproduces both sexually and asexually.


Figure 1. A sketch of Penicillium. Observe the paint-brush pattern that is characteristic of conidia formation by Penicillium species. Photo courtesy: https://www.microbiologyclass.com
  • Scopulariopsis: Fungi in the genus Scopulariopsis are common soil saprophytes. This genus contains fungal species that are anamorphic in nature; and they are also pathogenic to animals and humans. They have asexual forms or stages of reproduction – which allow them to form conidia. Morphologically, Scopulariopsis species form a distinct type of spore that appears as spiky/rough round conidia, usually in chains (Figure 2). Scopulariopsis species are commonly found in soil, dry walls, food, cellulose board, wallpaper, wood, mattress dust, decaying wood, and various other plant and animal products. Examples of fungal species in the genus Scopulariopsis include S. asperula, S. brumptii and S. brevicaulis. Clinically, S. brevicaulis causes deep mycoses; and the organism is notably resistant to antifungal agents. Scopulariopsis species are dermatomycotic molds and they have been associated with onychomycosis (i.e., fungal infection of the nails). They are common fungal contaminants in both the indoors and outdoors, but they also cause mycosis in humans, particularly in immunocompromised patients. Generally, Scopulariopsis species are known as saprobesbecause they feed on dead or decayed organic matter in the environment. Therefore, they undergo a saprotrophic mode of nutrition. This implies that Scopulariopsis species are saprobes.
Figure 2  A sketch of Scopulariopsis. Photo courtesy: https://www.microbiologyclass.com
  • Cladosporium: This is a genus of fungi that contain fungal organisms commonly found in indoor and outdoor environments. They cause the blackening of walls inside the house, especially during humid conditions. Cladosporium species are ubiquitously found worldwide; and the two common species are C. cladosporioides, C. oxysporum, and C. sphaerospermum, C. herbarum. They are commonly found in the air and on surfaces such as wallpaper or carpet indoors, especially where moisture is present. However, Cladosporium species can grow at low temperatures, and thus can cause contamination of refrigerated foods especially meat. Fungi in this genus parasitize plants, animals and other fungi. Cladosporium species rarely cause disease in humans but they can cause mycoses of the skin and toe nails occasionally. Morphologically, they form brown or black colonies on their substrates, and they have dark-pigmented conidia that are formed in simple or branching chains (Figure 3). Cladosporium species are significant allergens. In large amounts, spores of Cladosporium species can severely affect people with asthma and respiratory diseases who inhale these spores. Though they rarely cause human infections; Cladosporium species may occasionally cause mycoses of the skin, eye, sinus, and brain in immunocompromised individuals.
Figure 3. A sketch of Cladosporium species. Photo courtesy: https://www.microbiologyclass.com
  • Fusarium: Fusarium species are globally-distributed filamentous fungi that are abundant in the soil. They form both large conidia (macroconidia) and small conidia known as microconidia (Figure 4). Some fungi form phialides, from which their conidia develop, and this is applicable in fungi that undergo asexual reproduction such as F. solani. Phialides are bottle-shaped structures within which or from which conidia develop (Figure 5). Many Fusarium species are plant pathogens. They are major plant pathogens that affect agricultural plants in temperate regions, causing Fusarium infection known as Fusarium head blight in grains such as barley and wheat. Fungi in this group are known for their ability to produce toxins that have medical significance. Fusarium species are toxigenic in nature, and the mycotoxins produced by these fungi are often associated with animal and human diseases. When these mycotoxins enter the food chain, they can cause disease in human population. For example, Fusarium species cause onychomycosis (fungal infection of the nails) and mycoses of the cornea (keratomycosis). They also cause opportunistic infections in immunocompromised individuals. Many species of Fusarium found in the soil are harmless, and they undergo a saprotrophic mode of nutrition. F. moniliforme, F. solani, and F. oxysporum are examples of fungi in the genus Fusarium.
Figure 4. A sketch of microconidia and macroconidia of Fusarium species. Photo courtesy: https://www.microbiologyclass.com
Figure 5. A sketch of phialide types of sporulation. Some fungi form phialides from which their conidia develop. Phialides are formed during asexual stages of reproduction of some fungi such as Fusarium species. Photo courtesy: https://www.microbiologyclass.com
  • Fonsecaea: Fonsecaea is a genus that contains fungi implicated in causing chromoblastomycosis. Chromoblastomycosis is a localized fungal infection of the skin and subcutaneous tissues. Human infection usually occurs through the traumatic implantation of conidia or hyphal forms of the organism. Fonsecaea species are pleomorphic and sporulating in nature. They form spores or conidia used for reproduction and dispersal (Figure 6). Fonsecaea pedrosoi is a typical example of fungus in the genus Fonsecaea; and the organism grows as a soil saprotroph and can be pathogenic in humans. Saprotrophs are organisms whose mode of nutrition or feeding are saprophytic in nature (i.e., they feed on decaying organic matter). Fusarium species can also be found on trees and plants. Other likely pathogenic fungal species in the genus Fonsecaea include F. nubica and F. monophora. People who work in occupation where dusts particles can become easily aerosolized (for example, farmers) especially in endemic areas of the disease can easily develop chromoblastomycosis. 
Figure 6. A sketch of various types of sporulation of Fonsecaea pedrosoi. Photo courtesy: https://www.microbiologyclass.com
  • Exophiala: Exophiala is a fungal genus that contains fungi known as black yeasts. Exophiala species are ubiquitous fungi found worldwide, and they are dematiaceous in nature. Typical example is Exophiala dermatitidis, formerly known as Wangiella dermatitidis. E. dermatitidis is an imperfect thermophilic black mold that rarely causes infection in humans. However, people with compromised immune system are mostly at risk of acquiring infection with Exophiala dermatitidis. Exophiala dermatitidis is found in low abundance in nature; and the fungus occurs in the soil in decaying matter. It can also be found in dead plant matter in the soil. Exophiala species are saprobes that derive their nutrients from the decomposition or breakdown of dead organic matter in the soil. Exophiala species can be found in wet and moist man-made environments such as in pools. Exophiala dermatitidis is an anamorphic fungus that forms many conidia. The hyphal forms of E. dermatitidis shows fertile sterigmates of hyphae and conidiophore which are surrounded by spores or conidia during growth (Figure 7). E. dermatitidis also form black yeast forms on substrates (Figure 8). Fungi in the Exophiala genus cause subcutaneous and cutaneous opportunistic infections in endemic regions, especially in immunocompromised individuals. Pulmonary infections, liver infections and infections of the bone or joints are some of the infections in which E. dermatitidis is implicated as a causative fungal agent.
Figure 7.  Hyphal form of Exophiala dermatitidis. Photo courtesy: https://www.microbiologyclass.com
Figure 8. A sketch of black yeast forms of Exophiala dermatitidis. Photo courtesy: https://www.microbiologyclass.com

Further reading

Anaissie E.J, McGinnis M.R, Pfaller M.A (2009). Clinical Mycology. 2nd ed. Philadelphia, PA: Churchill Livingstone Elsevier. London.

Baumgardner D.J (2012). Soil-related bacterial and fungal infections. J Am Board Fam Med, 25:734-744.

Calderone R.A and Cihlar R.L (eds). Fungal Pathogenesis: Principles and Clinical Applications. New York: Marcel Dekker; 2002.

Champoux J.J, Neidhardt F.C, Drew W.L and Plorde J.J (2004). Sherris Medical Microbiology: An Introduction to Infectious Diseases. 4th edition. McGraw Hill Companies Inc, USA.       

Gladwin M and Trattler B (2006). Clinical Microbiology Made Ridiculously Simple. 3rd edition. MedMaster, Inc., Miami, USA.

Larone D.H (2011). Medically Important Fungi: A Guide to Identification. Fifth edition. American Society of Microbiology Press, USA.

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12th edition. Pearson Benjamin Cummings Inc, USA.

Stephenson S.L (2010). The Kingdom Fungi: The Biology of Mushrooms, Molds and Lichens. First edition. Timber Press.

Sullivan D.J and Moran G.P (2014). Human Pathogenic Fungi: Molecular Biology and Pathogenic Mechanisms. Second edition. American Society of Microbiology Press, USA.

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