2. • Most Fusarium species are soil fungi and have a worldwide distribution.
• Some are plant pathogens, causing root and stem rot, vascular wilt or fruit
rot.
• Several species have emerged as important opportunistic pathogens in
humans causing hyalohyphomycosis (especially in burn victims and bone
marrow transplant patients), mycotic keratitis and onychomycosis (Guarro
2013).
3. • Other species cause storage rot and are important mycotoxin producers.
• Currently the genus Fusarium comprises at least 300 phylogenetically
distinct species.
• 20 species complexes and nine monotypic lineages.
4. Morphological Description
• Colonies are usually fast growing, pale or bright-colored
(depending on the species) with or without a cottony aerial
mycelium.
• The color of the thallus varies from whitish to yellow, pink, red or
purple shades.
• Species of Fusarium typically produce both macro- and
microconidia from slender phialides.
5. • Macroconidia are hyaline, two to several-celled, fusiform to sickle-
shaped, mostly with an elongated apical cell and pedicellate basal cell.
• Microconidia are one or two-celled, hyaline, smaller than macroconidia,
pyriform, fusiform to ovoid, straight or curved. Chlamydospores may be
present or absent.
6. Cultures of F. oxysporum showing purple pigmentation and F.
subglutinans showing pink pigmentation.
7. • Fusarium chlamydosporum complex contains five phylogenetically
distinct species and is common in soils and the rhizosphere of numerous
vascular plants worldwide. It is occasionally isolated from human and
animal infections.
Fusarium chlamydosporum complex, culture showing
pink to ochraceous to brownish surface and a
carmine red reverse.
8. • Fusarium dimerum complex contains 12 phylogenetically distinct species
including F. delphinoides, F. penzigii and F. dimerum. These are regarded
as cosmopolitan saprotrophs in soil and on plant materials (Domsch et al.
2007). They have also been isolated from human corneal ulcers after
trauma and from disseminated or localised infections in
immunocompromised patients
Fusarium dimerum complex
culture showing orange to deep
apricot colour due to confluent
conidial slime, and macroconidia.
9. • Fusarium fujikuroi complex consists of 50 phylogenetically distinct
species including 13 of which have been reported to cause human
infection; F. acutatum, F. ananatum, F. andiyazi, F. fujikuroi, F.
guttiforme, F. napiforme, F. nygamai, F. verticillioides, F. proliferatum, F.
sacchari, F. subglutinans, F. temperatum and F. thapsinum.
• Fusarium incarnatum-equiseti complex consists of 40
phylogenetically distinct species. They occasionally cause infections in
humans and animals.
10. • Fusarium oxysporum complex contains at least five phylogenetically
distinct species and accounts for about 20% of human infections caused
by fusaria. All are ubiquitous soil borne pathogens responsible for
vascular wilts, rots, and damping-off diseases of a broad range of plants.
A number of these fusaria are also clinically important, causing localised
or deeply invasive life threatening infections in humans and other animals.
Mortality in patients who are persistently and severely neutropenic is
typically 100%.
11. • Fusarium solani complex contains at least 60 species and accounts for
about 50% of human infections caused by fusaria. All are ubiquitous soil
borne pathogens responsible for vascular wilts, rots, and damping-off
diseases of a broad range of plants. A number of these fusaria, notably F.
keratoplasticum, F. petroliphilum, F. lichenicola and F. solani are clinically
important, causing localised or deeply invasive life threatening infections in
humans and other animals.
12. Identification of Fusarium species is often difficult due to the variability
between isolates (e.g. in shape and size of conidia and colony colour) and
because not all features required are always well developed (e.g. the absence
of macroconidia in some isolates after subculture).
1. Colony growth diameters on potato dextrose agar and/or potato sucrose
agar after incubation in the dark for four days at 25˚C.
2. Culture pigmentation on potato dextrose agar and/or potato sucrose agar
after incubation for 10-14 days with daily exposure to light.
3. Microscopic morphology including shape of the macroconidia; presence
or absence of microconidia; shape and mode of formation of
microconidia; nature of the conidiogenous cell bearing microconidia; and
presence or absence of chlamydospores.
