Investigation of fungal contamination in indoor environments normally includes visual inspection and sampling. The samples to collect, the number, when and where to collect them and the methods to be used for sample analyses depends on the objectives or goal of the investigation. The samples that may be collected include air, dust or bulk samples. Swabs or clear cellophane tape can be used to sample for fungi from contaminated surfaces. The samples can be analyzed by either direct microscopy or by culture methods depending on the type of data required.
Indoor air quality is compromised by both biological and non-biological pollutants. Sources of biological pollutants include microorganisms, animal, insects and related organisms.
The most common biological pollutants of indoor air quality include molds and their byproducts, dust mites, pet dander (scales from hair, feathers, or skin), droppings and body parts from cockroaches, rodents and other pests or insects, viruses, and bacteria. Due to their small size, many of these biological pollutants are airborne and easily inhaled deep into the lungs.
Health Effects From Poor Indoor Air Quality
Some biological pollutants may cause serious health problems including hypersensitivity pneumonitis, allergic rhinitis, and some types of asthma. Other health problems attributed to biological pollutants are sneezing, watery eyes, coughing, shortness of breath, dizziness, lethargy, fever, and digestive problems.
It is believed allergic reactions occur only after repeated exposure to a specific biological allergen. The reaction may occur immediately upon re-exposure or after multiple exposures over time. It’s important to regularly monitor the indoor air quality.
What are colony forming units? Colony forming units, usually abbreviated as CFU, refer to individual colonies of bacteria, yeast or mold. A colony of bacteria or yeast refers to a mass of individual cells of same organism, growing together. For moulds, a colony is a group of hyphae (filaments) of the same mould growing together. Colony forming units are used as a measure of the number of microorganisms present in or on surface of a sample. Colony forming units may be reported as CFU per unit weight, CFU per unit area, or CFU per unit volume depending on the type of sample tested. To determine the number of colony forming units, a sample is prepared and spread or poured uniformly on a surface of an agar plate and then incubated at some suitable temperature for a number of days. The colonies that form are counted. CFU is not a measure for individual cells or spores as a colony may be formed from a single or a mass of cells or spores.
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
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