Why do some people get sick from mould and others do not? It is because of genetic and physiological differences. Sensitivity to mould in about 20 % of the human population is believed to be hereditary. Other factors that influence individual's resistance to mould include age and general health status. For example, infants, the elderly and those recovering from diseases may be at risk of mould exposure even at levels that would otherwise be considered "normal".

Susceptibility differences among individuals and the variability of moulds in their ability to cause health problems make it difficult to determine and set permissible exposure levels for indoor moulds.

Recently we were asked whether it would be OK to paint over mould on the shower ceiling. Painting over existing mould is probably not a good idea because the mould may continue growing beneath the paint film and subsequently the paint would start peeling off. The best solution would be to clean the mould following current mould remediation guidelines such as CCA 82 - Mould Guidelines for the Canadian Construction Industry and then find a way of reducing condensation in the shower. Painting after the mould has been cleaned and the condensation problems fixed would be OK.

I have always been fascinated by fungi. Fungi are a group of organisms to which moulds (mildews), yeasts, and mushrooms belong. Fungi used to be classified under the plant kingdom. However, they differ from plants in that they cannot make their own food and their cell wall is mainly made of chitin and glucan and not cellulose. Since they cannot make their own food, fungi have to survive as either saprophytes, parasites (pathogens) or by forming symbiotic relationships with their hosts. Saprophytic moulds are the ones commonly found in indoor environment growing on wall surfaces and other organic substrates. It is estimated that there are close to 1.5 million species of fungi but only about 100,000 species have been described.

My interest in fungi started when I completed my B.Sc. (Agriculture) and got employed as a plant pathologist. As a trainee plant pathologist, I spent countless hours in a plant clinic where farmers brought their diseased plants for diagnoses. My first fungus to identify without help was Entomosporium. One feature that makes me remember this fungus is the shape of the spores. The spores have appendages that make them resemble insects or two-legged mice with legs stretched sideways. I also went out into the field collecting diseased plants and taking them back to the laboratory for disease diagnoses and preservation as reference material. Working with diseased plants is not always easy because they won’t tell you where it is hurting (if at all they feel pain). You have to depend on symptoms and laboratory culturing and identification of the causative agent. If a plant is just wilting, for example, it is had to tell the cause of wilting which could be due to fungi, nematodes, bacteria, physical/chemical or physiological factors that interfere with water movement in the plant.

In my early days as a trainee, one challenge I had was to isolate the disease causing agent and getting pure cultures of the mould. It was not always easy because of the myriad saprophytic moulds and bacteria present on the surfaces of the plant. However, I learned quickly some clever ways plant pathologists and mycologists have developed to overcome the problem of contamination.

I was fortunate to be taught and interact with some of the world authorities in Mycology at CABI Bioscience (formerly the International Mycological Institute) and the University of Kent in the United Kingdom. These great people made me to like the subject.

My interest in fungi is now focused on indoor moulds. Indoor moulds are recognized health hazards and it is estimated that 20% of human population is sensitive to mould exposure. It is also believed that long-term exposure to mould could lead to sensitization.

Close to 100,000 species of fungi have been described. However, only a small number has been reported indoors. The most common indoor fungi include some species of Cladosporium, Aspergillus, and Penicillium. These may be found growing on damp wall surfaces in the basement, washroom, kitchen, windowsills, and ceiling tiles.

Below is a list of fungi that have been found in indoor environment. Click the name of the fungus (if the link is active) to get some details about its ecology and associated health effects where known.

Fungi that have been reported from indoor environment

Absidia corymbifera

Acremonium Species
Acremonium strictum

Alternaria Species
Alternaria alternata

Aspergillus Species
Aspergillus candidus
Aspergillus clavatus
Aspergillus flavipes
Aspergillus flavus
Aspergillus fumigatus.
Aspergillus nidulans
Aspergillus niger.
Aspergillus niveus.
Aspergillus ochraceous.
Aspergillus penicillioides
Aspergillus restrictus
Aspergillus sydowii
Aspergillus tamarii
Aspergillus terreus.
Aspergillus ustus
Aspergillus versicolor
Aspergillus wentii

Aureobasidium pullulans

Chaetomium globosum

Chrysonilia Species
Chrysonilia crassa
Chrysonilia sitophila

Cladosporium Species
Cladosporium cladosporioides
Cladosporium herbarum
Cladosporium sphaerospermum

Curvularia Species
Curvularia aureum
Curvularia geniculata
Curvularia lunata


Emericella nidulans (=Aspergillus nidulans)

Epicoccum nigrum

Eurotium Species
Eurotium amstelodami
Eurotium chevalieri
Eurotium herbariorum

Exophiala jeanselmei group

Fusarium Species
Fusarium culmorum
Fusarium oxysporum
Fusarium solani
Fusarium verticillioides (= Fusarium moniliforme)

Geomyces pannorum.

Geotrichum candidum

Gliocladium Species

Gliomastix murorum

Memnoniella echinulata

Mucor Species
Mucor hiemalis
Mucor mucedo
Mucor plumbeus
Mucor racemosus

Myrothecium verrucaria

Oidiodendron Species
Oidiodendron griseum
Oidiodendron tenuissimum

Paecilomyces Species
Paecilomyces lilacinus
Paecilomyces variotii

Penicillium Species
Penicillium aurantiogriseum
Penicillium brevicompactum
Penicillium chrysogenum
Penicillium citrinum.
Penicillium commune
Penicillium corylophilum
Penicillium crustosum
Penicillium expansum
Penicillium funiculosum
Penicillium glabrum
Penicillium janthinellum
Penicillium olsonii
Penicillium polonicum
Penicillium roqueforti
Penicillium rugulosum
Penicillium simplicissimum
Penicillium spinulosum
Penicillium variabile.
Penicillium viridicatum

Phialophora Species
Phialophora fastigiata

Phoma Species
Phoma glomerata
Phoma macrostoma

Pithomyces Species
Pithomyces chartarum
Pithomyces Species

Rhizopus stolonifer

Scopulariopsis Species
Scopulariopsis brevicaulis
Scopulariopsis candida
Scopulariopsis fusca
Scopulariopsis Species

Sistotrema brinkmanii.

Sporothrix Species
Sporothrix schenckii.

Stachybotrys chartarum

Stemphylium botryosum

Syncephalastrum racemosum


Trichoderma Species
Trichoderma harzianum
Trichoderma viride

Ulocladium Species
Ulocladium botrytis
Ulocladium chartarum

Wallemia sebi



References

With increasing grow ops in residential houses many home buyers, home inspectors and indoor air quality consultants wonder if there were some types of mould species that can be used as ‘fingerprints’ or indicators for homes formerly used for marijuana grow ops. Currently we are not aware of species of moulds that can strictly be associated with marijuana grow ops. However, the dominant moulds in a building environment are generally indicative of the moisture levels prevailing over a long period of time.

The environments tends to select and maintain certain micro-organisms as the “home microflora”. This “home microflora” is usually determined by the types of nutrients available, water activity, pH and temperature. In building environments, moisture is the growth limiting factor for moulds. Moulds differ in their water requirements. A small group of moulds requires high levels of available water (water activities of more than 0.9). This group, referred to as hydrophilic or tertiary colonizers can be used as indicators for water/moisture damaged buildings. Such moulds include species of Chaetomium, Fusarium, Memnoniella, Stachybotrys, Trichoderma, Ulocladium and a few others. The largest group of moulds requires continuous damp conditions (or water activities between 0.80 and 0.90). This group is referred to as secondary colonizers. Examples of secondary colonizers include common indoor contaminants such as Cladosporium spp and some species of Aspergillus and Penicillium. Another small group of noulds, the xerophilic or xerotolerant, is able to grow at water activities below 0.80. This group, also referred to as primary colonizers, include Aspergillus restrictus, Aspergillus versicolor, Eurotium spp., Penicillium aurantiogriseum, P. brevicompactum, P. chrysogenum and Wallemia sebi. Xerophilic moulds are indicators of relatively dry environments.

Moulds commonly associated with marijuana in storage include species of Aspergillus, Penicillium, Fusarium, Mucor, Rhizopus, Alternaria, and Curvularia. These moulds cannot be used as indicator moulds for marijuana grow ops since they are also found on many other substrates.

Secondary colonizers are likely to be the most common in houses used for grow ops but they are not unique to the grow ops. In conclusion no moulds are currently known to be strictly associated with marijuana grow operations.

It is widely accepted that mold growth in occupied places should not be allowed because of health risks. However, it is always debated as to whether mold testing is necessary in situations where growth is visible. Both mold assessment and mold testing are necessary as discussed below.

Mold Assessment
Mold assessment involves a qualified professional who would conduct a thorough inspection of the building. The key objectives of a mold assessment are to determine the underlying cause of mold growth and the extent of contamination. Mold assessment does not tell the investigator the types of molds growing in the building and whether these molds have contaminated the air.

Mold Testing
Would doctors prescribe antibiotics to patients with bacterial infection without testing to know which bacterium is causing infection? Similarly, a mold investigator requires to know whether the building is contaminated with toxigenic molds such as Stachybotrys, Aspergillus, Fusarium, or any of the close to 200 molds likely to be found in a water damaged building. The investigator may also want to know whether the air is already contaminated with spores from the visible growth and hence, they have to collect samples and send them to a reputable mold laboratory for testing.

From laboratory results and the visual assessment data, the investigator is able to give recommendations on the level of mold abatement required and the necessary protection for the workers and the building occupants. Read more about why test for mold at http://www.moldbacteria.com.

Recently we received some questions from Australia on why eating food contaminated with mould is dangerous. We have posted the questions here together with our brief answers.

Q. Can you still eat food once you chop the mould off?

A. It is risky to eat food that is already contaminated with visible mould. As mould grows it tends to produce by-products (secondary metabolites) that permeate into the food or material it is growing on. Some strains of moulds such as those belonging to Aspergillus, Penicillium and Fusarium produce metabolites that are highly toxic.

Q. If there are foods you can eat after chopping mould off, what are they?

A. I would not recommend eating of any food that has previously been contaminated with mould because the person eating the food may not be knowing which mould is contaminating the food and whether the mould has produced toxins.

Q. What kind of moulds are unsafe to eat? Why?

A. All moulds are generally unsafe to eat. However, the risk is higher if one is to eat those moulds known to produce toxins (the so called toxigenic moulds). Some examples of toxigenic moulds commonly found on food are species of Aspergillus, Penicillium and Fusarium. Some species of these moulds are known to produce highly toxic metabolites. A good example is Aspergillus flavus which produces Aflatoxin. Recently aflatoxin killed 125 people in Kenya after eating contaminated maize.

Q. What are the conditions that are best for producing the toxins in toxigenic moulds?

A. The conditions that trigger toxin production by moulds are not well understood. However, genetic and growth conditions are known to influence toxin production. Growth conditions that may influence toxins production are food nutrient composition, pH of the food, moisture content and temperature.

Q. If mould is present on food, does this necessarily mean that bacteria causing food poisoning is also present?

A. If mould is present on food, this does not necessarily mean that bacteria causing food poisoning are also present.

Q. What are some of the symptoms that can be caused by eating toxigenic moulds? Are any fatal?

A. Symptoms of mycotoxin poisoning may depend on the root of entry into the body.

1. Inhalation symptoms may include: nose and throat pain, nasal discharge, itching and sneezing, cough, wheezing, difficult breathing, chest pain and bloody sputum.
2. Ingestion symptoms may include: nausea, vomiting, and watery or bloody diarrhea with abdominal pain.
3. Contact Symptoms: burning skin pain, redness, and blurred vision (if the eyes are affected).

Severe poisoning can lead to death. Some Mycotoxins such Aflatoxin can also trigger cancer.

Q. Are there any ‘safe’ moulds that you can eat? Are there any moulds that may improve health by eating them?

A. There are no ‘safe’ moulds to eat. However, some moulds including some that are known to produce toxins have been used for many years in production of fermented food. Quorn is a high protein fungal product produced from a species of Fusarium. It is used as an alternative to animal protein.

Q. Can you mistake bacteria for mould? ie. do any look similar to the naked eye?

A. Bacteria and moulds are totally different organisms. Their cell structures are different. Their mode of growth is different and therefore easy to differentiate.

We would be happy to use this blog for answering questions on indoor mould and bacteria. If you have a question that you want answered on this blog please send it to us at http://www.moldbacteria.com/questions.html. If we don't have the answers, we will research them for you.