Airborne Bacteria In Indoor Environments

Significance Of Airborne Bacteria In Indoor Environments

Indoor airborne bacteria have not received as much publicity as the mould. Are indoor airborne bacteria of health significance?

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Bacteria are found virtually in every environment including the hot springs, deep-sea hydrothermal vents, glaciers, swamps, and mines! Some heat-loving bacteria (hyperthermophiles) thrive best above 176 °F (80 °C) whereas the psychrophiles (cold-loving) can survive far below 0 °C.

In indoor environments bacteria are present in air and on surfaces. High levels of bacteria concentration indoors is an indication of high occupancy rate, poor ventilation, or poor building maintenance. Similar to mould, some bacteria are associated with water-damaged building materials.

Significance Of Airborne Bacteria

While bacteria do not receive as much publicity as mould when it comes to indoor air quality, they are a health hazard. Some are serious human pathogens and others especially the gram negative bacteria produce toxic compounds (endotoxins) from the outer membrane of their cell wall. Endotoxins may have a role in sick building syndrome.

Indoor airborne bacteria can loosely be categorized into bacterial pathogens and environmental bacteria associated with water-damaged building materials. Bacterial pathogens are capable of causing severe diseases in humans if inhaled, ingested or if they come into contact with the skin. The most important airborne bacterial infections in indoor environments are tuberculosis, nosocomial pneumonia, and legionellosis. These infections are primarily acquired through inhalation of the causative agents.

Environmental bacteria generally associated with mouldy building materials include Acinetobacter, Bacillus, Flavobacterium, Nocardia, Streptomyces, and Thermomonospora. Also associated with water-damaged material are the filamentous bacteria, the Actinomycetes. Some airborne bacteria such as Staphylococcus spp and Micrococcus spp are dispersed into the air from human skin, oral and nasal surfaces, and hair. These bacteria are associated with nosocomial infections in health care facilities.


Sampling For Airborne Bacteria

Bacteria Colonies On TSA Agar MediaThe commonly used sampling method for airborne bacteria is the impaction of air onto agar media using volumetric samplers such as Andersen, SAS, or RCS. Samples can also be collected by impingement into liquid media. However, for routine air quality monitoring agar based sampling is recommended. Trypticase soy agar (TSA) media is usually used when sampling for bacteria. It is important to select a medium suitable for growth of the target organism, for example when sampling for some specific bacteria such as Legionella. Sampling time depends on the sampler used but generally not more than 10 minutes. Shorter times are recommended in heavily contaminated areas. Samples are kept cool and shipped for overnight delivery to the laboratory for incubation and identification of the dominant species.


    1. Chin, S. Yang, Patricia A. Heinsohn (Editors). Sampling and analysis of indoor microorganisms. 2007. John Wiley & Sons, Inc.(ISBN-13:978-0-471-73093-4
    2. 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).
    3. 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.


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