Typically, indoor air samples should be dominated primarily by Gram positive cocci and to a lesser extent Gram positive non-sporulating bacilli. These organisms are recognized in indoor air as originating primarily from human sources such as shedding human skin and mucous membranes. High levels of Bacillus species in the indoor air generally indicate the presence of past water damage and/or a lack of maintenance either in the HVAC system or in the building as a whole or both. Elevated levels of Gram negative bacilli usually indicate an interior source that warrants further investigation. Because Gram negative bacilli are subject to relatively rapid desiccation outside a moisture source, their presence at high levels is of concern. Actinomycete contamination of indoor environments is often accompanied by other microbial contaminants.
Raw sewage can contain a wide variety of pathogenic organisms including Salmonella, Shigella, enteric viruses, Giardia, Cyptosporidium, and multicellular parasites. Sewage may also contain blood-borne pathogens such as HIV and the virus that causes hepatitis. There are microorganisms such as Escherichia coli and Enterococcus that are common to raw sewage that are used as indicators of contamination, as well as to verify the effectiveness of remediation procedures. The presence of these organisms in building materials following a sewage backflow is a clear indication of sewage contamination. Typically, Escherichia coli will initially be more numerous in freshly contaminated samples than Enterococcus, however, as materials dry out the hardier Enterococcus will survive longer.
Micrococcus, Staphylococcus, and Streptococcus are human associated. They come from people and are common indoors. If the concentration is elevated, it may suggest high human activity.
The presence of some common environmental bacteria, such as Actinomycetes (especially the thermophiles) in indoor environments is of concern because of their ability to produce hypersensitivity pneumonitis in exposed individuals, as well as their opportunistic pathogenicity potential. The presence of high levels of actinomycetes indoors requires immediate further investigation.
Following sewage events in structures, bacteria pathogens in sewage (including gram-negative organisms Salmonella, Escherichia coli, and Shigella) represent risk to the occupants, especially those that contact the water. Following extraction of the water and drying of the structure, the cell walls of the bacteria (endotoxins), which are prone to become airborne, can produce toxic effects.
Some healthy people host human-associated bacteria, such as Staphylococcus aureus, that is pathogenic and may be communicated to people with compromised immune systems (e.g. “Staph infection”).
When to test for bacteria: