Water activity (aw) refers to “free” water available for microbial growth. For microbial growth to occur, moisture must be freely available. The water activity of a material determines which types of mold would grow on that material.
Technically, the water activity is defined as the ratio of the vapour pressure exerted by the water in the material to the vapour pressure of pure water at the same temperature and pressure. Check out our Mold Inspection, Identification and Control course to learn more about Water Activity.
Indoor molds vary in their water activity requirements and this ranges from 0.7 to >0.9. Higher aw materials tend to support the growth of more microorganisms. Unlike molds, bacteria usually require a water activity of at least 0.91 aw. Molds can be grouped according to their moisture requirements as follows:
Check out our Mold Inspection, Identification and Control course to learn more about Types of Mold.
Note:
Water damage may occur over many months, mainly through roof leakage, but also via rising damp and defective plumbing, which result in mold growth. Indoor molds as well as bacteria are usually saprophytic, meaning that they obtain nutrients from dead organic matter. The nutrients are from the breakdown of simple to complex sugars such as starches, cellulose and pectin. The materials most susceptible to mold growth are organic materials containing cellulose (i.e. jute, wallpaper, cardboard and wooden materials). The tertiary colonisers are used as the indicators of moisture damage. The table below shows some of the most common indicators of water damage in buildings.
Indicators of excessive moisture or chronic condensation
Molds indicative of moisture or chronic condensation in a building | |
Alternaria alternata | Phialophora sp |
Aspergillus fumigatus | Fusarium sp. |
Chaetomium spp | Ulocladium sp. |
Trichoderma (some species) | Yeasts (Rhodotorula spp.) |
Exophiala sp. | Memnoniella echinata |
Stachybotrys chartarum (synonym S. atra) |
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The post Water Activity Requirements For Mold Growth appeared first on Mold Testing and Bacteria Testing.]]>The spores of Aspergillus fumigatus are very small. Having a diameter of 2–3.5 µm, they are easily inhaled deep into the lungs. It is estimated that people inhale at least several hundreds of spores of Aspergillus fumigatus per day without harm. However, Aspergillus fumigatus is an opportunist pathogen (Hazard Risk Group 2) and can cause a lung infection (aspergillosis), in people with weak immune system. Most of the cases of aspergillosis are caused by this fungus. Because of its potential role as an opportunist pathogen, there is concern about high concentrations of Aspergillus fumigatus spores in the vicinity of hospitals, where those with compromised immune system such as organ transplant and cancer patients, may be at increased risk of infection. Therefore, monitoring for airborne spores in hospitals especially during renovations is a good practice.
Aspergillus fumigatus naturally occurs in decaying organic material, but because it is a thermotolerant fungus it grows well at raised temperatures experienced during the composting process. Within the indoor environment, A. fumigatus belongs to the group of indicator microorganisms typical of moisture-damaged buildings such Stachybotrys, Chaetomium, Fusarium and Ulocladium. The following characteristics make A. fumigatus a ubiquitous opportunistic pathogen: 1) ability to survive and grow in a wide range of environmental conditions, 2) effective dispersal in the air, 3) physical characteristics that allow spores to reach deep into the respiratory system, and 4) ability to swiftly adapt to the host environment.
In hospital environment, air sampling may be conducted to monitor air quality during construction, to verify filter efficiency, or to commission new space prior to occupancy. Because aspergillosis cases have occurred when airborne fungal spore concentrations ranged as low as 0.9–2.2 colony-forming units per cubic meter (CFU/m3) of air, it is suggested that an air volume of at least 1000 L (1 m3) should be considered when sampling highly filtered areas.
Malt extract agar (MEA) can be used to sample for Aspergillus fumigatus. For selective isolation of A. fumigatus, a high incubation temperature of 37 to 40 is then used as this inhibits growth of other saprophytic fungi.
Mold spores are common in household and workplace dust. Also, due to their light weight, mold spores are often floating in the air both outdoors and indoors. Inhaling mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Allergic reactions to mold spores are common. They can be immediate or delayed. Mold spores can also cause asthma attacks in people with asthma who are allergic to mold.
We breathe in mold spores and fragments every day, indoors and outdoors. Usually these exposures do not present a health risk. However, health problems may result when people are exposed to large amounts of mold, particularly indoors.
In about 20 percent of people, the immune system overreacts and causes the allergic response resulting in symptoms such as runny nose, scratchy throat and sneezing. Most of us know this allergic illness as “hay fever” or “allergic rhinitis.”
If you have an allergy that never ends when seasons change, you may be allergic to mold spores. Allergic symptoms from outdoor mold spores are most common in summer.
It is impossible to get rid of all mold spores indoors; some spores will be found floating through the air and in house dust. However we can reduce the amount of spores in our homes by controlling mold growth. The mold spores will not grow if moisture is not present. Therefore, indoor mold growth can and should be prevented or controlled by controlling moisture indoors. If there is no mold growth indoors then the only source of spores would be outdoors. Spores originating from outdoors may not be in amounts that would present a health problem. If there is mold growth in your home, you must clean up the mold and fix the water problem. If you clean up the mold, but don’t fix the water problem, then, most likely, the mold problem will come back.
Although there are many types of molds, only a few dozen are known to cause allergic reactions. Alternaria, Cladosporium, Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus and Aureobasidium are the major culprits. Some common mold spores can be identified easily in a laboratory when viewed under a microscope.
The spores can be actively released or passively released depending on the type of mold. The release of spores is also influenced by environmental conditions. Some spores are released in dry, windy weather. Others are released with the fog or dew when humidity is high.
Indoor air sampling for mold is important for several reasons. Mold spores are not visible to the naked eye and the only way to determine whether the air is contaminated and the types of mold present is through laboratory analysis of the air samples. Having air samples analyzed can also help provide evidence of the scope and severity of a mold problem, as well as aid in assessing human exposure to mold. After mold removal, new samples are typically taken to help ensure that the amount of airborne mold spores has been successfully reduced.
Air samples can be used to gather data about mold present in the interior of a house. Samples are taken using a pump that forces air through a collection device which catches mold spores. The sample is then sent off to a laboratory to be analyzed.
The post Mold Spores In Air And Health Issues appeared first on Mold Testing and Bacteria Testing.]]>People often talk of black mold or mildew in their bathroom, ceiling, basement and kitchen.
The question you may ask, is it a single type of mold? No. In most cases, more than one type of mold will be growing on the same surface. At least 150 mold species have been reported from residential and commercial buildings. Fortunately, not all of these are harmful to most people, so even if you suspect mold growth, don’t panic; but make you have it tested at the earliest.
If you want to know more about specific molds, visit the Mold Library.
If you are looking for a professional to help you with mold testing or remediation, contact us to discuss your situation further.
Exposure to indoor mold has been associated with the following health problems:
The level of moisture (usually referred to as water activity) in building material determines not only whether mold will grow or not but also the types that colonize the material. Damp materials with a water activity value equal to or greater than 0.90 are usually colonized by strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp.
Materials with a water activity value ranging from 0.90 – 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.
A study conducted in Denmark found that water leakage through roofs, rising damp, and defective plumbing installations were the main sources for water damage with subsequent mold growth.
The building materials most susceptible to mold attacks were water damaged, aged organic cellulose containing materials such as wood, jute, wallpaper, and cardboard. In this study, the molds that were most frequently encountered were Penicillium (68%), Aspergillus (56%), Chaetomium (22%), Ulocladium (21%), Stachybotrys (19%), Cladosporium (15%), Acremonium (14%), Mucor (14%), Paecilomyces (10%), Alternaria (8%), Verticillium (8%), and Trichoderma (7%). These molds are all known to cause different types of inhalation allergy. The species most frequently encountered were Stachybotrys chartarum, Penicillium chrysogenum, and Aspergillus versicolor.
If you’re interested in learning more about mold and bacteria, you can explore the links above to the left. If you’re curious or concerned about anything not covered here, please use the Question Form.
Interested in having an in-depth understanding? Check our Resources page which will provide you with links to other educational materials.
The post Mold Information appeared first on Mold Testing and Bacteria Testing.]]>Metalworking fluids (MWF) is the name given to a range of oils (mineral -petroleum, animal, marine, vegetable or synthetic oils) and other liquids that are used to cool and/or lubricate metal works during machining, grinding, cutting, milling, etc. There are four basic classes of Metalworking Fluids:
Although each class will vary greatly in composition, each may contain additives such as sulphurized or chlorinated compounds, corrosion inhibitors, extreme pressure additives, emulsifiers, biocides, stabilizers, dispersants, defoamers, colorants, dyes, odorants and fragrances.
Although metalworking fluids are used throughout the industry by hundreds of thousands of workers safely, problems can develop when good hygiene practices are not followed or when fluids are not properly managed or maintained.
Bacterial and fungal contamination of metalworking Fluids (MWFs) is a major concern in the industries which use these fluids. It may cause equipment malfunction, off-odors, degradation in the fluid quality, economic losses and finally, they pose as a major health hazard. Several Gram +ve and Gram -ve bacteria are found as contaminants. These include Staphylococcus sp., Bacillus sp., Pseudomonas sp., Proteus sp. and Coliforms. Amongst the fungi, Aspergillus sp., Penicillium sp., Fusarium sp. and Cephalosporium sp. are found to be prevalent.
Major health concerns of improperly managed Metalworking fluids include skin irritation, allergic contact dermatitis, irritation of the eyes, nose and throat, and, occasionally, breathing difficulties such as bronchitis and asthma. There is also evidence that some MWFs are associated with an increase in risk of certain cancers such as larynx, rectum, pancreas and skin.
Most bacteria and fungi enter the system through the water supply, debris and build up in any equipment like hoppers, conveyors and sump pump. Therefore, it is highly recommended by experts to perform monitoring of metalworking fluids, associated machinery and pipe work, periodically, to ensure quality and safety.
At MBL, we perform total mould and bacterial counts of the samples to help you monitor quality standards of MWFs. MBL provides you with a Report of Analysis that indicates levels of mold and/or bacterial contamination and what can be regarded as good, reasonable or poor standards of fluid management.
Following are the acceptable indicator levels used to determine the standard of the fluids and required action:
Comparing your counts with these levels will help you decide the quality of your metal working fluid. It will also help you select the treatment method if contamination is detected and economize performance.
Should you have a question concerning contamination of metalworking fluids or our services contact us via email, or fill out our Question Form and submit for priority attention. Your questions will be answered within 48-72 hours. For immediate assistance call 905-290-9101.
The post Metalworking Fluids Bacteria and Fungi appeared first on Mold Testing and Bacteria Testing.]]>Building molds and yeasts such as strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp. grow well on very wet building materials.
Materials with a water activity value ranging from 0.90 – 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.
In some countries building molds have been grouped into 3 hazard classes based on associated health risk. These classes are similar to risk groups assigned to microorganisms handled in laboratory environments.
See which hazard class each of the common building molds belong to at Common Indoor Molds.
Yes. Building occupants need assurances that they were not exposed to building molds that may cause health problems. Some of the objectives for laboratory testing are:
References
Gravesen S, Nielsen PA, Iversen R, Nielsen KF. (1999). Microfungal Contamination of Damp Buildings–Examples of Risk Constructions and Risk Materials. Environmental Health Perspectives, Supplements Volume 107, Suppl 3:505-8.
Sedlbauer, K., (2002): Prediction of mould fungus formation on the surface of and inside building components. Doctoral Dissertation, Fraunhofer Institute for Building Physics.
“Eating mouldy bread is discouraged. Where can I find the facts that prove this? Are there moulds that grow on bread that are harmless? Some of my patients that survived food shortages in The UK during World War II by eating mouldy bread and other foods insist that such fears about mould are unfounded”.
Those are the comments/questions that we received and below we explain why eating mouldy food should be discouraged.
It is true that people may eat mouldy food without any harm. In many cases, children and adults who live on the streets in developing countries survive on food and fruits thrown into waste bins. Most of these foods and fruits are usually contaminated with mould and bacteria.
The major reasons why eating mouldy food is dangerous is because such food is likely to be contaminated with mycotoxins (i.e., fungal poisons).
Luckily, moulds that produce toxins (also called toxigenic moulds) require certain growth conditions to produce the toxins and hence presence of these moulds on food does not necessarily mean the food contains mycotoxins.
There is also a high risk of food poisoning caused by bacteria such as Staphylococcus aureus, Salmonella, Clostridium perfringens, Campylobacter, Listeria monocytogenes, Vibrio parahaemolyticus, Bacillus cereus, and Entero-pathogenic Escherichia coli.
Mycotoxin poisoning is primarily through ingestion and to some extent through contact. The effect of poisoning by mycotoxin is called mycotoxicoses. There are several documented (and probably more undocumented) cases of mycotoxicoses both in human and domesticated animals.
Yes. In fact some moulds are used in the processing of food especially in Asian countries. The following are some of the moulds used in processing of foods.
Feeding on food or feed contaminated with mould is risky and should be avoided at all times. Eating such food could result to food poisoning either due to mycotoxin or bacterial contamination or both.
The post The Risks of Eating Mouldy Foods appeared first on Mold Testing and Bacteria Testing.]]>In agriculture Fusarium is known to cause diseases of many economically important crop plants. Some species are known to colonize stored cereal grains not only causing losses but also producing mycotoxins such as trichothecenes, zearalenone, and fumonisins that are harmful to humans and animals(1, 3).
In the medical field, the species cause opportunistic infections of human eyes, skin or nails and may also cause systemic infections in individuals with weak immune system. The most important species as far as human infection is concerned are Fusarium solani, F. moniliforme (=Fusarium verticilloides), F. oxysporum and F. dimerum (1, 3). Fusarium solani is also allergenic and is occasionally found in indoor environments. It affects 4% of nasobronchial allergy patients (4).
Some of the infections attributed to some species of Fusarium are:
In the industrial environment, Fusarium species are known to contaminate industrial products such as pharmaceutical solutions or machine cooling fluids. Fusarium keratitis has been in the news as the cause of severe fungal eye infections through contamination of contact lens solution.
Fusarium species do not grow well at low water activity levels and will usually colonize very damp or wet material, hence, presence of Fusarium in a building is an indication of a water problem. Fusarium may produce three types of spores: namely, macroconidia, microconidia, and chlamydospores (3).
The macro and microconidia are the most likely to become airborne, but since they are produced in wet form they do not easily become aerosolized unless the mould is completely dry. Indoor airborne spore counts for Fusarium are therefore rarely high. A few spores of this fungus indoors could be an indication of serious mould growth.
Airborne microconidia and chlamydospores are difficult to identify and for air samples analysed by direct microscopy, only the macroconidia of some species may be reported. It is therefore possible that Fusariumspores (especially the microconidia) are usually lumped together with other unidentified spores.
For viable samples it is important to note that desiccation affects viability of Fusarium spores and therefore a few colony forming units (CFUs) would also be an indication of a problem.
According to Health Canada, persistent presence of significant numbers of Fusarium species and other toxigenic moulds such as Stachybotrys chartarum, Aspergillus and Penicillium requires further investigation (2).
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References
Ulocladium (you-low-clay-dee-um) is a genus of saprophytic, darkly pigmented fungi. Ulocladium species are cosmopolitan and are commonly found in the soil and on decaying herbaceous plants, paper, textiles, dung, emulsion paint, grasses, fibres and wood.
In buildings, Ulocladium is commonly found in damp or wet areas such as bathrooms, kitchens and basements and around windows. It is frequently isolated from painted surfaces, damp wall finished with wallpaper or water based emulsion paint; floor and mattress dust. It grows on very wet walls and particleboard. Because of its high water requirements it is considered an excellent indicator of water damage.
Ulocladium has two known species; Ulocladium chartarum and U. botrytis.
U. chartarum is the species most commonly found in indoor environment. Its presence in indoor environment together with other molds such as Stachybotrys, Fusarium and Chaetomium is an indication of water damage.
Ulocladium has been reported to cause Type I (hay fever) allergy. There have been cases of U. chartarum causing skin surface and deep skin infections in immuno-suppressed patients. U. botrytis has no proven pathogenicity.
Alternaria (all-tur-nair’-ee-uh) is another dark-colored mold. Alternaria species are among the most abundant fungi. It’s very closely related to Ulocladium. Alternaria can cause allergic reactions. It’s common in dust, around windows, damp areas, in soil, on foodstuffs, textiles, and on plants. Exposure to Alternaria can provoke respiratory and asthmatic symptoms in susceptible persons.
If this article was helpful, you may also benefit from reading our list of common household moulds.
The post Ulocladium appeared first on Mold Testing and Bacteria Testing.]]>Plant parasitic Fusarium causes wilting of many plants including crops such as tomatoes, bananas, sweet potatoes, pigeon peas, and pears. Some species of Fusarium are commonly isolated from seeds, especially those of cereals.
In addition, this common species of fungus can produce a number of different mycotoxins which include trichothecenes (T-2 toxin, HT-2 toxin, deoxynivalenol (DON) and nivalenol), zearalenone and fumonisins. The Fusarium species are probably the most prevalent toxin-producing fungi in the northern temperate regions and are commonly found on cereals grown in the temperate regions of America, Europe and Asia. These toxins have been shown to cause a variety of toxic effects in both experimental animals and livestock and are also suspected of causing toxicity in humans.
In indoor environments Fusarium species are generally found under very wet conditions. They are commonly isolated from carpet and mattress dust, damp walls, wallpaper, polyester polyurethane foam, humidifier pans and areas where stagnant water occurs in HVAC systems. Some species cause keratitis in humans, and infect eyes and finger nails. Fusarium species are also an inhalation hazard.
F. culmorum is soilborne and has a worldwide distribution. Indoors, it has been isolated from floor, carpet and mattress dust; damp wall and polyurethane foam.
Fusarium culmorum is associated with allergy. It also produces vomitoxin, a trichothecene mycotoxin that causes a serious feed refusal and vomiting in animals fed contaminated feed.
F. solani is a soil borne fungus found indoors in carpet and mattress dust; damp walls, wallpaper; polyester polyurethane foam; insulating cotton in duct liner; water pipes and humidifiers.
F. solani causes keratitis in humans. It is also associated with wounds and infections of the eyes and fingernails. It poses inhalation and deep skin (dermal) inoculation health risks to persons with weak immune systems. It also poses health risks related to major barrier breaks such as corneal perforation, major surgery, peritoneal or venous catheter presence, and injection drug use.
F. verticillioides is soilborne. Indoors, it is found on humidifier pans and other areas where stagnant water occurs in HVAC systems. Also found in mattress dust, and on damp walls.
F. verticillioides causes keratitis in humans and invasive mycoses in immunocompromised people. It poses inhalation and deep skin (dermal) inoculation health risks to persons with weak immune systems. F. verticillioides also poses health risks related to major barrier breaks such as corneal perforation, major surgery, peritoneal or venous catheter presence, and injection drug use.
You can learn more about our Fusarium mold testing service here.
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