Lately there has been many misconceptions about what fungi is. Many have wrongly used the words mold and fungi interchangeably and others have missed the mark entirely by referring to it as bacteria.
Fungi (singular: Fungus) is a group of living organisms that are distantly related to plants, and more closely related to animals, but which are very different from these groups. In the aim to classify all living organisms the Kingdom system was formulated. There are five kingdoms: Prokaryotes, Protists, Plants, Animals and Fungi. The kingdom fungi are made of: yeasts, mushrooms and molds (the dreaded organism [Fig. 1]).
Figure 1: Types of Fungi
Fungi can be helpful and harmful. Some helpful fungi include Saccharomyces cerevisiae (yeast used in baking) others used in making blue cheese and some edible mushrooms such as Morels and Shiitake. However, the harmful fungi have taken the spotlight lately as they have been associated with adversely impacting human health. Apart from the well-known disease causing fungi such as Candida Albicans (a type of yeast which causes yeast infections) (Fig. 2) ¸ molds are now seen to survive in human tissue as well (de Hoog et al, 2015).
Figure 2: Various forms of Candidiasis caused by Candida Albicans.
Molds form long filaments known as hyphae and under stressful conditions produces spores (resistance structures). Molds are considered the ‘weeds’ of the fungal kingdom as they grow on many natural substrates (surfaces) such as plant tissues, wood and bark, insects and other arthropods and other fungi. They are also associated with food spoilage, and also contaminate many manufactured materials such as wood, paper and textiles, and are frequent visitors to the indoor environment (Seifert et al, 2011), associated with a number of human health ailments. It is the saprophytic nature of molds which makes them destructive as they are not capable of producing their own food. And as a result they secrete enzymes which break down whatever they are growing on. When the enzymes dissolve the substrate, the hyphae are used to absorb the nutrients.
Molds fall into three hazard classes: those which are allergenic, pathogenic or toxigenic. However, mold produces a characteristic musty/moldy odour which is associated with actively growing mold. this odour is associated with the production of volatile organic compounds (VOC) or microbial volatile organic compounds (mVOC) (Brandt et al, 2006).
Mold exposure can be through three pathways: skin contact, inhalation and ingestion, with inhalation being the most prevalent route of exposure. Mold spores (viable [living] and non-viable [dead]) can impact human health. Some spores are aerodynamically favourable (2 – 10 um in size) which makes it easy to be inhaled. These can be deposited in either the upper or lower respiratory tract. However, spores need to be aerosolized (airborne) in order for them to be inhaled (Brandt et al, 2006). This normally occurs when disturbed by inexperienced, unknowledgeable individuals or through natural disturbances. It should be noted that the longer a susceptible individual remains in a moldy environment, the greater the possibility of impact.
Prepared by: Ermine Herman
References
1. Brandt Mary et al (2006) Mold Prevention Strategies and Possible Health Effects in the Aftermath of Hurricanes and Major Floods. National Centre for Environmental Health, CDC.
2. de Hoog G.S., Guarro J., Gene J., Figueras M.S., (2015) Atlas of Clinical Fungi. CBS-KNAW Fungal Biodiversity Centre, Urecht.
3. Seifert Keith, Morgan-Jones Gareth, Gams Walter, Kendrick Bryce (2011) The Genera of Hyphomycetes CBS-KNAW Fungal Biodiversity Centre, Urecht.