Topic 16 - Mycotoxicosis - human and animal poisonings of microfungi Flashcards
Fungi
Unicellular, or multicellular organisms (without tissues) developing hyphae
Sessile, heterotroph organisms feeding on dead matter, or living tissues
Secrete extracellular digestive enzymes into the environment and adsorb dissolved molecules
1.5-10 million species worldwide’
Symbiotic fungi
Two thirds of all fungi
Mutualists or parasites
Fungal community role in predators (humans)
community of anaerobic microfungi in the intestines; pathogenic microfungi (digestion, parasites)
Fungal community role in herbivorous animals (livestock)
community of anaerobic microfungi in the intestines, in the rumen; pathogenic microfungi (digestion, parasites)
Fungal community role in photosynthetic plants (crop plants)
community of mycorrhizal fungi, endo-phytic microfungi (nutrient uptake, com-mon mycorrhizal network, protection)
Fungal community role in community of terricolous saprotrophic fungi
mineralization (ammonification), biological weathering, sharing of nutrients among plants
Production of secondary metabolites
Produced primarily when sources of nutrients become limited in the environment
Support (stabilise) the primary metabolism
Biosynthesised from the primary metabolites → strictly regulated
Number of secondary metabolites is generally high, once produced do not considerably affect the stability of primary metabolism
alternative origin of secondary metabolites
Horizontal gene transfer from bacteria
Biological functions of secondary metabolites in fungi
Support the acquisition and defence of nutrient sources against other organisms
Protection from UV radiation
During sexual reproduction, attract the hyphae of the opposite sex then play a key role in cell differentiation during ontogeny
Toxic heavy metals and poisonous chemical compounds
Depend on environment and the species identity of the fungus
Pb: passive accumulation along roadsides (in the past, from exhaust fume)
Some fungal genera are characterised by the active accumulation of Cd (from the brake pads of vehicles)
Hg: some Agaricus species (with a yellowing flesh) and puffballs accumulate it specifically; it can also be accumulated passively in many other taxa growing on crop fields
Accumulation of insecticides and herbicides
Radioactive materials in fungi
Fungi able to accumulate large amounts of radioactive isotopes within a short time period due to extensive mycelia and the huge total surface of hyphae
K+ ions can be replaced with cesium ions → can be taken up easily from acidic soils
fungi preferring acidophilus haibitats → higher in cesium
Toxins
concentration of toxins accumulated by soil fungi increases towards the higher trophic levels (thus highest in comminites in predators)
Food safety should be considered from the soil microbes
Health hazards caused by fungi
Allergy
Mycetism
Mycotoxicosis
Mycosis
Allergy
allergic reactions to fungal spores and/or to other fungal substances
Mycetism
mushroom poisoning; ingestion of toxic substances present in macro fungal sporocarps
Mycotoxicosis
Poisonings caused by the toxic compounds of microfungi (mainly holds) that readily colonise crops and human foods
Mycosis
Infection of animals and humans by pathogenic microfungi (mainly holds, yeasts)
Mycosis in fish
Saprolegnia: Caused by saprolegnia species through wounds
Generally secondary pathogens affecting usually overfed individuals with other infections, and kept in dirty and too cold water
Symptoms of mycosis in fish
Skin with cotton-like structures
Often covered by algae
Treatment of mycosis in fish
Quarantine
alteration of circumstances suitable for fungal infections
Mycosis in amphibians
Devastating amphibian populations worldwide
Batrachochytrium dendrobatidis and B. salamandrivorans cause lethal skin infections in frogs and salamanders, respectively
Mycosis in reptiles
Infections difficult to recognise, often overlooked
Circumstances perfect for fungal infections: many individuals are crowded in a small box, and kept in sub-optimal temperatures with high air humidity
Most frequently, their skin and mucous membranes are affected
Mycosis in birds
Aspergillosis most frequently affect respiratory system including air sacs
Poultry highly susceptible
Cryptococcosis rarely develop in birds, but a large population of Cryptococcus neoformans lives int heir intestines → humans can be infected in cities from the droppings of pigeons
Mycosis in humans (mammals)
Fungal infection in case of Immune deficiency: HIV infection, long-term application of broad-spectrum antibiotics, radioactive radiation, cancer, autoimmune diseases, neutropenia, diabetes, skin burns, catheter, intravenous drug use
infect skina nd mucous membranes
Subcutaneous infections (injuries)
Infection of internal organs
They are often difficult to cure → prevention
Mycotoxicosis
Never induce immune response
Symptoms: often occur when major organ damage is developed
approx. 150 micro fungal taxa
Most important mycotoxins detected in forages and human foods
Aflatoxins Ochratoxins Trichothecenes Zearalenon Rubratoxins Ergot alkaloids
Aflatoxins
Produced mainly by Aspergillus flavus and A. parasiticus
grow mainly on fleshy forages and oil plants damaged by insects
Effects of microfungi producing aflatoxins
mutagens, teratogens, immunosuppressives, cause hepatic impairments (hepatitis, liver chirrosis and cancer)
Ochratoxins
Nephrotoxins causing necrosis of renal tubules, immunosuppressive, carcinogenic
Fat-soluble compounds → pork fat is rich in ochratoxins;
too much consumption of coffee and rye bread should be avoided
By A. ochraceus, A. carbonarius, Penicillium verrucosum
Fumonisins
Affecting white matter of horse brain → leucoencephalomalacia
Structural analogues of sphingosine → disruption of sphingolipid metabolism → erosion of myelin sheath of axons
Carcinogenic
Trichothecenes
Inhibit protein synthesis
Large subunit of ribosomes is affected
Produced by fusarium species
All cereals and gras species are potential hosts
Zearalenon
Interferes with sexual maturation
Pigs particularly sensitive, humans not
Enlarged outer genitals; atrophic ovaries → sterility
In corn flakes and beers made of maize
Produced by fusarium species
Rubratoxins
Cause damage in liver and kidneys; also affecting the CNS
Trigger the effects of aflatoxins
Eggs, dairy and meat products can be rich rubratoxins
Produced by penicillium and Aspergillus species
