Aspergillus flavus

Aspergillus flavus is a potentially dangerous pathogen. It is a fungus with a very widespread distribution.  It grows in soils as a saprophyte. It also grows on cereal grains, legumes, and tree nuts.

In addition to causing pre-harvest and post-harvest infections, many strains produce toxic compounds known as mycotoxins. If eaten, they are toxic to mammals. The toxin produced by this species is called 'aflotoxin'.

A. flavus is a human and animal pathogen. In mammals, the pathogen can cause liver cancer if contaminated food is eaten. It also causes aspergillosis (invasive growth) in people whose immune system is damaged.

 How deadly is it? 
In 1960 on an English farm, about 100,000 turkeys died. The cause of death was the primary food source, peanut meal. It was infected with A. flavus. The culture was isolated, grown in pure culture, and a subset of healthy turkeys was infected. The pure culture isolate causes death in the healthy turkeys. There were four toxic chemicals (aflatoxins).

Turkey autopsies showed aflatoxins targeted the liver and either completely killed the tissue cells or induced tumor formation. New standards for the production of food for human consumption were developed, which led to increases in cost.

 Crop management 
To keep grains and legumes remain free of A. flavus infection, some things must be done before, during, and after harvest. Moisture levels should be kept below 11.5%. Temperature in storage units should be kept as low as possible: the pathogen cannot grow below 5°C. The low temperature slows respiration and reduces moisture.

Fumigation reduces insects and mites, otherwise they help the spread of the pathogen. Removing old, unripe, damaged and broken seeds, and cleanliness also keeps down the spread of the pathogen.

 Biological control 
 Yeast 
To protect tree nuts and corn plants that are affected by A. flavus  treating the plants with the yeast Pichia anomala reduces the growth of A. flavus. Treating pistachio trees with P. anomala inhibited the growth of A. flavus up to 97% when compared to untreated trees.   The yeast successfully competes with A. flavus for space and nutrients, ultimately limiting the growth of A. flavus.

 A.flavus AF36 
The good news is that there is a non-harmful strain which outcompetes the pathogenic strains.

Aspergillus flavus strain AF36 is not carcinogenic and is toxin-free. It is used as an active ingredient in pesticides. AF36 is a fungal antagonist and is applied as a commercial biocontrol to cotton and corn to reduce aflatoxin exposure. AF36 is grown on sterile seeds which serve as the carrier and a source of nutrients. After application and colonization, AF36 growing seeds will out-compete aflatoxin-producing strains of A. flavus. Non-aflatoxin spore dispersal is aided by wind and insects.

 References 

 Other websites 
How safe is mouldy food to eat? BBC News magazine. 

Category:Moulds