The goal of biological sampling is to help determine whether the biological particles present in a particular environment are affecting or causing irritation in certain individuals. Sampling is also used to locate the sources of indoor microorganisms and facilitate an effective remediation. While we are typically surrounded by a wide variety of different microorganisms every day, sampling provides us with a method to establish in a scientific way whether the environment in question contains more organisms than would normally be present.


Bacteria are everywhere. We can’t function without them, but we often only hear about the bad guys. Bacteria, often referred to as “germs,” are microscopic organisms that are present in water, soil and air, on and in animals, plants and man. They are bigger than viruses (which are only visible using an electron microscope), but smaller than molds (or fungi). They are able to multiply quickly, and need little in the way of “food.” Since they are everywhere, all they really need to grow is water, just like molds. They are responsible for bad smells in the refrigerator and in damp basements (along with molds), evil smells in the bathroom (many of those smells are due to anaerobic bacteria: organisms that don’t like to grow in air), and some of them cause disease. The slimy film that coats your celery in the refrigerator is due to the growth of cold-resistant bacteria on the food, with the production of “biofilm.”

Why do we sample for Bacteria?

  1. Hospitals house sick patients. These people are very vulnerable to high levels of bacteria and mold. Hospitals need to know they are not infecting their patients, or allowing high numbers of organisms to be present in their environment. Patients with little or no immune systems (immunocompromised) can “catch” almost anything.
  2. Pharmaceutical clean rooms need to be just that (see # 4 above).
  3. Water we drink should be “clean.” It should not contain sewage organisms at any level (see # 2 above). The sewage screen is a useful tool to show that our drinking water is good, or that the sewage leak was cleaned up properly.
  4. Legionella is not a good thing in our hot water systems or in cooling towers: remember the Bellevue hotel in Philadelphia in the 70s? It was dead for some years because Legionnaires’ disease broke out in the hotel.
  5. Because the client is concerned about bacteria in his/her environment.

AN IMPORTANT NOTE: You will not always find what you are looking for. Some pathogens are rarely found in the air: they are either too sensitive to its drying effects, or they are overgrown by competing environmental organisms. This does not mean they are not there, and is one of the reasons why “indicator organisms” are used for sewage screens. The gastro-enteric organisms, such as Campylobacter, Shigella, and even Salmonella, are almost never found in water, which is why we look for E.coli, fecal Strep., fecal and total coliforms in our sewage screens. Except for total coliforms, if any of these are present, then so is sewage, and by implication the Bad Guys. Presence of total coliforms only indicates dirt, but not sewage.

What will the results look like?

  1. Sewage screens generally provide presence or absence of the indicator organisms (we can provide numbers for fecal coliforms and fecal Strep.).
  2. Legionella testing will provide presence or absence of Legionella pneumophila in the submitted specimens.
  3. Bacterial count and gram stain will provide enumeration (in colony-forming units, or cfu, per mL, per gram, or per cubic meter of air, depending on the specimen submitted) and gram stain morphology of bacteria present.
  4. Identification of three (or five) predominant types will identify up to three (or five) predominant types of bacteria, predominance referring to the numbers present.

While there are no published standards or guidelines for bacteria in air, it is generally felt that a high level of gram-negative rods in the air is unhealthy, especially of those bacteria associated with sewage. Presence of Legionella in water systems, fecal organisms in drinking water, or high levels of environmental organisms in a clean room or operating room are, however, not acceptable.