Biological agents in indoor environments

Search: Marc Hamilton, Microbiologist, Laboratory President Environex


Biological agents are substances that come to be alive or living beings are capable of causing disease or adverse effects on other biological organisms, the human being in particular.

These substances or living creatures include parasitic pathogens, non-infectious microorganisms such as fungi and algae, plants and their by-products(1).


Microorganisms are living organisms, imperceptible to the naked eye(2). They exist without causing adverse effects in several types of environments in the ground, in the atmosphere, in water, on and within animals, plants, and food on the inside and outside of the human body. Some microorganisms are likely to cause problems in our immediate environment.

The microorganisms that cause disease are called pathogens. Others become pathogenic in certain circumstances they are called opportunistic organisms. They become pathogenic under optimal conditions only. To survive, microorganisms need moisture and food sources. The main sources of moisture buildings are generally identified as the condensation on windows, poorly insulated ductwork, water leaks, etc.. Pathogens often produce substances called toxins that can cause problems in the host. Many of these toxins cause symptoms of various diseases of the microorganism itself3. Toxins are chemicals secreted by fungi (mycotoxins) and bacteria (endotoxins).


Bacteria are microscopic living cells with a relatively simple structure. They are unicellular.

Bacterial infections that reach the middle contracted by respiratory, gastrointestinal or during inoculation bite, scratch, scratch and cut. Bacteria in the air come from two sources aerosols generated by water such as humidifiers, faucets, showers, etc.. or those caused by humans or animals.

Saprophytic bacteria (microbes that live in the wild at the expense of decaying organic matter) and pathogens are dispersed in the air by humans when sneezing, coughing and talking. What are bacteria can survive for periods whose duration depends on the size of the projected droplets, the temperature of the air, the relative humidity and the presence of a substrate for travel.

It is usually assumed that the transmission of disease from person to person may be by aerosol exposure, but few people know that the bacteria carried by the water, which are present in the environment can multiply. These same bacteria can be hidden inside buildings and cause disease. Some types of bacteria are found in contaminated ventilation systems humidifiers. They cause the syndrome called "humidifier fever". This syndrome is a response to allergens transported by air include endotoxins of many grams-negative bacteria. Endotoxins can cause fever, leukocytosis or leukopenia (low white blood cells) in humans(4). Moreover, exposure of the skin to certain bacteria can cause dermatitis (skin disease), etc.

Molds and fungi

The fungal kingdom consists of diverse organizations, including forms macroscopic (visible to the naked eye, such as those that are edible for example), as well as microscopic structures (invisible to the naked eye). These organisms are ubiquitous in nature and play a key role in the recycling of organic matter. They are also often called "sacrophytes" That is to say, organisms nutritious organic matter decomposition. Unlike plants, they do not produce chlorophyll and feed by absorbing external sources of carbon.

Although they are responsible for some human diseases, fungi, including yeasts and molds can be good(4). They reproduce by fission, by budding or by spores that come from some distinctive fruity species(5) structures. The diameter of the spores of interest is approximately (5) microns and they are mainly found in the ambient air. Particles of this size are inhalable and therefore deposited in the lung alveoli (4) (cause or could cause respiratory problems).

Fungi can cause disease in several ways by the toxins they produce (mycotoxins) by allergens they can (be, for biologically active constituents of their cell wall constituents of their shell that can cause a dry cough , irritate the skin, eyes and throat) and cell polyclonal activators.


1.ALHA, Biohazards Committee 1985. Biohazards Reference Manual. American Industrial Hygiene Association, 160 pages.

2.Regnault, Jean-Pierre, General Microbiology. Decarie Vigot, 1990. 859 pages

3.Price. A.T et al. Biological Hazards, the Hidden Threat. Nelson. London, 1981, 89 pages.

4.Group work on fungi in the air inside buildings. Health and Welfare Canada, 1986.

5.Pelczar, M.J. and Reid. R.D. Microbiology. McGraw-Hill. Toronto, 1972