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Description of Indoor Environment Biological Agents

Research: Marc Hamilton, Microbiologist, President, Eurofins EnvironeX


Biological agents are substances originating from living organisms or are living organisms capable of causing harmful effects or diseases on other biological organisms such as the human being in particular.

Those substances or living organisms include the infectious parasitic agents, the non-infectious micro-organisms such as mushrooms and algea, plants and their by-products1.



Microorganisms are live beings, not detectable to the naked eye2. They exist without causing harmful effects in many types of environments, in the soil, in the atmosphere, in water, on and inside animals, plants, food and inside and outside the human body. Some microorganisms are prone to cause problems in our surrounding environment.

Disease causing microorganisms are called pathogenic organisms. Others may become pathogenic only under certain conditions. They are called opportunistic organisms. They become pathogenic under optimal conditions only. To survive, the microorganisms need sources of moisture and food. The main sources of building moisture are generally identified as being window condensation, poor ventilation ducts insulation, water infiltration, etc. Often, pathogenic microorganisms produce substances called toxins, which may cause problems for their hosts. Many of those toxins cause disease symptoms different from the microorganism itself3. Toxins are chemical products secreted by some fungus (mycotoxins) and bacteria (endotoxins).


Bacteria are microcospic living cells having a relatively simple structure. They are unicellular.

Environment induced bacterial infections are caused through respiratory and digestive tract or through inoculation from stings, grazes, scratches and cuts. Ambiant air bacteria originate from two sources, i.e. aerosols generated by water such as humidifiers, faucets, showers, etc., or those generated by humain beings or animals.

Saprophyte bacteria (microorganism living in nature from organic matter decay) and pathogens are dispersed in the air by humain beings when they sneeze, cough and speak. Those bacteria may survive during periods which are directly proportionate to the size of the droplets sprayed, to the air temperature, to its relative humidity and to the presence of a travelling substrate.

It is usually recognized that disease transmission from one person to another may be done through an exposition to an aerosol, but a few people know that the waterborne bacteria which are present in an external environment can multiply. The same bacteria can be dissimulated within buildings and trigger some diseases. Some types of bacteria are found in contaminated ventilation system humidifers. They would cause a syndrome called ”humidifier fever”. This syndrome is a response to airborne allergens which include the endotoxins of a fair number of gram-negative bacteria. Endotoxins may induce fever, a leukocytosis or leukopenia (leukocyte number reduction) in human bodies4. Moreover, the epidermis exposition to certain bacteria can cause dermatitis (skin disease) etc.

Moulds and fungus

Fungus are made of diversified systems including macroscopic shapes (visible to the naked eye such as the edible kind for example), as well as of microscopic structures (invisible to the naked eye). These organisms are found anywhere in nature and play a prime role in organic matter recycling. They are often referred to as “sacrophytes” i.e. systems being fed by decaying organic matter. Unlike plants, they do not produce chlorophyl and are fed by absorption of external sources of carbon.

Although they are responsible for some diseases for human beings, fungus, including yeast and moulds can be beneficial4. They breed by fission, by budding or by spores stemming from certain species’ distinctive fruity structures5. The diameter of spores which is of interest to us, is approximately (5) micrometers and those are found mainly in the ambiant air. Particles of that size are inhalable and consequently settle on pulmonary alveoli4 (cause or may cause respiratory problems).

Fungus can cause illnesses in many ways through the toxins they produce (mycotoxins), through they may produce, through cellular wall active biological components (their husks’ components which may trigger a dry cough, throat, eye or skin irritation) and through polyclonal cell activators.


  1. ALHA, Biohazards Committee 1985. Biohazards Référence Manual. American Industrial Hygiene Association, 160 pages.
  2. Regnault, Jean-Pierre, Microbiologie générale. Décarie Vigot, 1990. 859 pages
  3. PRICE. A.T et al. Biological Hazards, the Hidden Threat. Nelson. London 1981, 89 pages.
  4. Groupe de travail sur les champignons dans l’air à l’intérieur des édifices. Santé et bien être social Canada, 1986.
  5. Pelczar, M.J. and Reid. R.D. Microbiology. McgrawHill. Toronto, 1972