Various methods can be used to collect bacteria samples. The procedure will depend on what is being sampled and the type of data required. One may may be interested in a specific bacterium, in which case the method of sampling should be suitable for the recovery of that specific organism.
Sampling from surfaces
Sampling of bacteria from surfaces is usually performed using sterile swabs. Results from this test could be as simple as presence or absense of the bacterium of interest for example E. coli or Legionella. The test could also be detailed to include the amount of the bacterium present. It’s important to know how to collect samples for these different levels of analysis. If quantification is required, it’s important to swab a known surface area, for example 100 cm square. In this case the results would be expressed as “Number of colony forming units” per unit area.
Sampling bacteria samples from the air
To sample bacteria from the air, the air is impacted on some suitable growth media. The media to use will be determined by the type of bacteria being sampled for. If one is interested on a specific type of bacterium then a media that is selective for that bacterium should be used. To sample for the general population of bacteria in the air, then a media that can support the growth of many types of bacteria such as tryptic soy agar (TSA) should be used. Results are given as colony forming units per cubic meter of air.
Sampling for bacteria from water
Testing water for bacteria involves collecting a water sample in a sterile container and sending it to the lab for testing. The test results may just indicate the presence/absence of the bacterium of interest or may be detailed to include the amount present in terms of colony forming units per mililitre.