Chromogenic Identification of Indicator Organisms in Compressed Air

Trace Analytics, LLC – the leading compressed air testing laboratory since 1989

Chromogenic Identification – Indicator Organisms

Indicator organisms are often used as an early-detector that signals the presence of pathogens that require immediate investigation and remediation. Microbial contamination can affect food, pharmaceutical, medical device, or packaging manufacturers and can have devastating effects.

Compressed air that comes in direct or indirect contact with end-products presents a risk when the air is contaminated with microbes. For example, microorganisms such as Listeria can cause a recall, a plant shut down, or consumer illness. Regular testing for indicator organisms in compressed air can reveal contamination that could put users and consumers in danger.

What to test for:

There are many dangerous organisms that can exist in compressed air. To determine exactly what to test for, manufacturers must perform a risk assessment. Some products might be more at risk for Salmonella, while others more prone to E. coli contamination.

The following are indicator organisms that Trace Analytics can identify:

test for dangerous indicator organisms

An average of over 20 food manufacturers each year issue recalls due to Listeria alone (FDA, 2018). Recalls are costly and potentially devastating. Bacteria like E. coli, Salmonella, Listeria, and Shigella can harm consumers and put manufacturers at risk of shut down for re-validation.

Because oil and water contamination, and lack of preventative maintenance on air distribution systems all act to create an ideal habitat for microorganisms, it’s important to employ proper dryers and filtration. Point-of-use filtration helps to protect the product from any contamination in the air system. However, anything from routine maintenance, to a leak, to an inadequate filter can allow for dangerous contamination to enter the system. Regular testing is critical to ensure that the system is functioning properly.

Since warm, dark, and moist environments are ideal for microbial growth, it is important to keep your compressed air clean and dry. Find more information on testing for particles, water, and oil here.

Sampling and Analysis:

sampling compressed air for microorganisms

To facilitate these tests, an SAS Pinocchio Super II Impaction Sampler can be purchased or rented from Trace Analytics. Detailed instructions and step-by-step videos are available to ensure that microbial sampling is easy and straightforward. The media plates are then shipped overnight back to Trace Analytics for analysis.

First, our trained microbiologist conducts a total plate count (TPC) and Gram stains for bacteria. This type of enumeration can be done in aerobic and anaerobic environments for your compressed air or gases (e.g. oxygen or nitrogen), respectively. Bacterial classification by Gram stain can be done for all bacteria present on the sample plate.

Once these steps are complete, our microbiologist can then perform chromogenic identification of indicator organisms. Most indicator organisms require a different, specialized media. An AirCheck expert can help determine the appropriate media. Organisms are then reported as present or not detected. The chromogenic indicator organism identification is available only as an add-on to our microbial Pro Package.

indicator organism identification

Organisms are identified by the changing colors on specialized agar as shown above. Different organisms will react by changing color on the appropriate specialized media. Use your risk assessment to determine which bacteria to test for and ask your AirCheck expert about the appropriate sampling media to determine whether or not dangerous organisms are present.


Our state-of-the-art microbiology laboratory and expert microbiologist can handle all of your testing needs. Contact us for more information on microbial testing and indicator organism identification.

Chromogenic organism identification can be added to the Pro Package as outlined below. Contact our service team for more information.

chromogenic identification pricing