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.
Moulds commonly found in carpet and mattress dust
A number of moulds are frequently found in carpet and mattress dust. Eurotium repens is the most frequently detected mould in mattress dust. Others include Aureobasidium pullulans, Alternaria alternata, Penicillium chrysogenum, Aspergillus penicilloides and Aspergillus restrictus.
More than 100 species of moulds have been recorded from carpet dust. As with mattress dust, the most frequently isolated mould in carpet dust is Eurotium repens. The others are Penicillium chrysogenum, Alternaria alternata, Aureobasidium pullulans and Phoma herbarum.
Concentrations of these moulds in carpet and mattress dust can be as high as 70 million colony forming units per gram of dust. Such high concentrations of moulds are likely to cause respiratory allergy or irritating symptoms. Therefore, it is import to regularly HEPA vacuum the carpets, mattresses and upholstered furniture to reduce the dust and spore concentration. If people are suffering from reoccurring respiratory allergy or irritating symptoms in a building where there is no visible mould, it is suggested that dust be tested for the types and concentrations of mould present.
Legionella: Health Effects, Occurrence and Sampling
Health effects of Legionella
In 1976, in Philadelphia, USA, over 200 attendees of the US-American Legion, developed pneumonia. The disease was later called “Legionnaires’ disease”. The causative agent, a Gram-negative bacterium, was named Legionella pneumophila. Legionella pneumophila causes 85-90% of all cases of Legionella infections (legionellosis). There are over 40 species of Legionella.
Legionella pneumophila can cause very severe infection of the respiratory system. However, Legionnaires’ disease epidemics are rare but the disease is fatal if untreated. The disease may develop within 2 to 13 days (average 5-6 days).
Another form of legionellosis is Pontiac fever, named after an outbreak in 1968 in Pontiac, USA. This form of disease, caused by a number of Legionella species, is milder than Legionnaires’ disease. Pontiac fever develops within 48 to 72 hours and the illness may clear in 2-5 days. No fatal cases have been reported in relation to Pontiac fever. This disease mainly appears as epidemics. Pontiac fever is believed to be a reaction to inhaled Legionella antigens rather than an infection.
Disease transmission
There is no evidence for transmission of legionellosis from person to person or by ingestion. Legionella infection occurs when people inhale the bacterium via fine water droplets as aerosols from the environment. Indoor transmission of legionellosis has been reported via contaminated hot water supplies in hospitals, hotels and other public buildings, respiratory therapy equipment, jacuzzis, spas and air-humidifiers.
Occurrence
Legionella bacteria are part of the natural aquatic bacterial population of lakes and rivers. They are present in all types of fresh water, including tap water. Legionella multiply in water, using other microorganisms like bacteria, algae and protozoa. Their concentration in fresh water is influenced mainly by the temperature. They are isolated more frequently and in higher concentrations from warm water (30 to 50 °C.). However, Legionella also survive at much lower temperatures indoors as well as outdoors. At temperatures above 60 °C Legionella can’t survive.
Sampling Of Legionella
Sampling of Legionella in indoor air or water on a routine basis is not recommended. However, sampling is recommended to:
- determine the source of outbreaks of legionellosis
- check the effectiveness of maintenance practices and control measures for hot water supplies and humidified ventilation systems
- guarantee the safe use of hot water supplies and humidified ventilation systems.
When investigating the water services within a building for Legionella, the condition of pipes, the joining methods used, the presence of lagging, sources of heat, and the standard of protection afforded tanks should be noted, as well as disconnected fittings, ‘dead-ends’, and cross-connections with other services.Water Sampling
Water samples should be collected in sterile autoclavable plastic containers. The samples should be taken from:
- the incoming supply;
- tanks;
- an outlet close to, but downstream of, each tank;
- the distant point of each service;
- the water entering and leaving any fitting under particular suspicion.
Surface Sampling
Using swabs, surface samples should be taken from shower heads, pipes and taps. Also, sludge, slime or sediments within building water services or humidifiers can also be collected, particularly where accumulation occurs.
Sample Handling and Storage
Samples should be stored at room temperature (20 ± 5 °C.) in the dark and should be processed within 2 days. That means the samples should be sent to the laboratory within 24 hours. It is also important to confirm with the lab that they have the necessary media before sampling is done.
Air sampling
The presence of Legionella in indoor air can be investigated using Reuter Centrifugal Sampler (RCS) or the Andersen sampler. Regardless of the sampler used, the recommended sampling agar at present is BCYE-agar.
References
- Flannigan, B., R.A. Samson, and J.D. Miller (Editors). Microorganisms in home and indoor work environments: diversity, health impacts, investigation and control. 2001. London, UK: Taylor & Francis (ISBN: 0-415-26800-1).
- Wanner, H-U, AP Verhoeff, A Colombi, B Flannigan, S Gravesen, A Mouilleseux, A Nevalainen, J Papadakis, and K Seidel. 1993. Biological Particles in Indoor Environments. Indoor Air Quality and Its Impact On Man. Brussels: Commission of the European Communities. Report No. 12.
For more information on indoor bacteria, please visit http://www.moldbacteria.com/ or call 905-290-101.
How Fast Does Mould Grow On Building Materials?
Under experimental conditions moulds are found to cover artificially inoculated building materials in 4-10 days. For example, fast growing strains of Stachybotrys chartarum produce visible mould growth on new water-damaged gypsum boards in 5 days. Slow growing strains of Stachybotrys take 14 days to completely cover the test materials. These observations suggest that visible mould growth could appear within 1-3 weeks after water damage. Under natural conditions mould growth is influenced by a number of factors.
Key factors that determine how fast mould grows
- Type of mould: All moulds don’t grow at the same rate. Some moulds grow faster than others. For example, under the same conditions of growth, Ulocladium would grow faster than Stachybotrys.
- Temperature: Moulds grow faster at or closer to their optimal temperature for growth. For most indoor moulds the optimal temperature is around 25 °C. However, mould can still grow at temperatures as low as -7 °C. Some species of Cladosporium and Penicillium are capable of growing on wood at -5 °C although spore germination requires at least 0 °C. At low temperatures mould growth is very slow.
- Water activity: Growth rate of mould increases with increasing water activity. Most indoor moulds have their optimal water activity at 0.96-0.98. Lowering the water activity of the material lowers the growth rate significantly. However, a few species such as some species of Aspergillus, Penicillium, Eurotium and Wallemia are able to grow at lower water activities. Germination of spores requires slightly higher water activity than the minimum required for growth.
- Age of the spores: Older spores require longer time to germinate than relatively younger spores.
- The spore load: If a building is full of settled viable spores, mould would cover a wider area in a shorter time, than, if there were a few settled spores.
- Composition of the building material: Most building materials derived from plants are highly susceptible to mould attack. For instance, wallpaper allow fast growth for cellulolytic moulds such as Chaetomium and Stachybotrys.
- pH of the material: pH of the material strongly influences the rate of mould growth, sporulation and metabolite production. Some moulds such as Aspergillus fumigatus grow best in the pH range from 4-7 and less well at acidic and basic extremes.
- Nutrient availability in the material: Growth could be unrestricted if all nutrients are in excess but restricted when not all nutrients are in excess.
- Presence of antimicrobial compounds in building materials: Some building materials contain antimicrobial compounds. These compounds slow down mould growth.
- Competition with other micro-organisms: In a moisture damaged environment, there is a great diversity of microorganism. These microorganisms (including bacteria) compete for nutrients and also produce by-products that may inhibit the growth of other microorganisms. Fast growing moulds tend to over-grow slow growers.
Conclusion
Since there are many factors that influence mould growth in buildings, it is hard to say when mould growth started. However, if we know where and when the moisture problem started, we could speculate how long the mould growth has been there.
References
- Nielsen, K. F. (2002). Mould growth on building materials. Secondary metabolites, mycotoxins, and biomarkers. Ph.D. Thesis. BioCentrum-DTU, Technical University of Denmark.
- Nielsen, K. F., Holm, G., Uttrup, L. P & Nielsen, P. A. (2004). Mould growth on building materials under low water activities. Influence of humidity and temperature on fungal growth and secondary metabolism. International Biodeterioration & Biodegredation, 54(4) 325-336
For more information on mould growth, please visit http://www.moldbacteria.com/ or call 905-290-101.
Mould Exposure
The best strategy to determine if building occupants are exposed to hazardous mould is to take air samples. It is important to note that even in rooms with visible mould growth air sampling may give very low spore counts. Two methods are widely used in sampling air for mould.
- Impacting air on some growth media. This method is used when one is interested in determining the concentration of viable mould spores/fragments in the air.
- Impacting air on some inert sticky surface. In this case the mould spores and other particulate are directly counted under a microscope regardless of whether the spores are viable or not.
Both methods have limitations. Therefore, whether to use the first, second or both methods depends on the type of data required, which in turn depends on the objective of the investigation.
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