The major factors affecting growth of mould are nutrients, temperature, light, aeration, pH and water activity.

Nutrients
Nutrient requirements for moulds may vary from mould to mould. Some moulds may thrive well on substrates with high sugar or salt content. Some may prefer simple sugars while others have the ability to utilize complex sugars.

Temperature
The majority of moulds are mesophilic, i.e., they can grow at temperatures within the range of 10-35°C. Optimum temperatures for growth may range between 15 and 30°C. However, some moulds such as Chaetomium thermophilum and Penicillium dupontii are thermophilic, i.e., they can grow at 45°C or higher and fail to grow below 20°C. A few moulds are psychrophilic and are unable to grow above 20°C. A significant number are psychrotolerant and are able to grow both at freezing point and at room temperature.

Light
Many moulds species grow well in the dark, but some prefer daylight or alternate light and darkness for them to produce spores.

Aeration
Nearly all moulds require air to grow.

pH.
Moulds differ in their pH requirements. Most will grow well over the pH range 3-7. Some such as Aspergillus niger and Penicillium funiculosum can grow at pH 2 and below.

Water activity
All moulds require moisture for growth but the amount required varies widely. Moulds that are capable of growing at very low water activity are referred to as xerophiles, for examples Eurotium species and Wallemia sebi. Those that are capable of growing at very high water activity are referred to as hydrophilic, e.g., Stachybotrys, Chaetomium and Ulocladium.

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When investigating microbial contamination in an industrial setting, it is important to have an idea of the possible contaminants and sources of contamination and the stages in processing where contamination of the product or raw material is more likely to occur.

The occurrence and significance of microbial contamination in an ecological niche are determined by a number of factors as well as properties of the species concerned and the product. The factors include:

1. The primary contamination
Contamination may be:

• Intrinsic- i.e., of raw materials
• Extrinsic- i.e., during or after processing
• General- i.e., from air, soil and water
• Carriers- i.e., human/animals

2. Environmental factors and properties of the raw material/product
Another thing to consider is the environmental factors. The environmental factors may include pH and water activity of the product or raw material, available nutrients, and the ambient temperature. These factors determine what micro-organism(s) would be the dominant contaminant(s) and the level of spoilage of the product or raw material.

Investigating the problem
The first thing is to tour the plant and analyse in detail the stages of processing or production and using microbiological knowledge identify the stage(s) in the entire production process where possible contamination is likely to occur. The contamination of raw materials or the product may originate from contaminated air or equipment. Therefore, microbiological analysis of the product/raw material, the air and any equipment at the processing stage where contamination is suspected to occur should form the initial part of investigation.

We can help troubleshoot microbiological contamination problems in industrial, public buildings and hospital environments. For help with mould and bacteria testing and identification call us at (905)290-9101.

In many indoor environments such as public buildings, residential homes, hospitals, food industries (production, processing and storage), food eating places (restaurants, hotels etc) monitoring, at regular intervals, of air or surface contamination by moulds and bacteria is recommended. Monitoring would help in detecting changes in microbial diversity and concentration and hence taking the necessary action before a major problem occurs such as a disease outbreak, spoilage of food in case of a food industry or a compromise in air quality.

The monitoring should involve visual inspection and sampling of air and surfaces. This does not have to be an expensive undertaking if conducted by a professional who understands the basic biology and ecology of micro-organisms.

If you need information on monitoring of moulds and bacteria in air and on surfaces, please click Information Request to fill a form with details of your request.

Mould allergies are primarily caused by spores although particulate hyphal fragments may also induce allergic reactions. It is estimated that about 20 percent of the human population is hereditary allergic to mould spores, pollen grains and other particulates at levels that may be considered “normal”.

Activities such as hay making, harvesting of crops, composting, demolition of mouldy buildings and mould remediation can result to very high concentrations of allergenic spores that would sensitize majority of people. Exposure to high concentrations of spores may lead to a type of allergy referred to as hypersensitivity pneumonitis. This may be characterised by flu-like illness with cough; recurrent “pneumonia”; breathlessness and other respiratory problems.

Also, in closed environments such as indoors, mould spore concentrations can be very high particularly if the building is mouldy with poor ventilation. In indoor environment one may be exposed to toxigenic moulds such as Aspergillus spp, Penicillium spp, Fusarium spp, and Stachybotrys spp or less toxigenic but allergenic moulds such as Alternaria spp, Cladosporium spp, and Ulocladium spp.

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