Culturable Air Sampling Guide (Fungi or Bacteria)
Particle Impactors (Andersen-type Samplers)
This method of air sampling involves drawing a measured volume of air over culture media in Petri dishes. The Petri dishes are incubated in the laboratory so the organisms impacted on the plate can grow. The fungi or bacteria are counted and identified. This method commonly uses an Andersen N-6 type impactor (e.g. EMSL VP-400 Microbial Sampler Product ID 8709001). Different agar plates are available from EMSL Analytical, Inc., depending on the types of fungi or bacteria to be identified.
Benefits
- Fungal cultures can determine whether the fungus is viable (alive), and allows for genus and species identification.
- Bacterial cultures provide enumeration and identification of culturable bacteria present in the air.
Disadvantages
- Cultures take 6-10 days for the microorganisms to grow and be identified.
- Since most environmental samples contain a large number of organisms, each has to compete with others to grow on the media. As a result, fungi and bacteria present in the air may not be as well represented in culture.
- Some microbes do not grow well or at all on the culture media.
- Some microorganisms are unable to be identified, as they fail to produce key characteristics such as spores or they may not be described in the scientific literature.
General Media Recommendations Fungi and Bacteria
- For fungal sampling, in general, we recommend Malt Extract Agar (MEA).
- If you are sampling in dry areas, the use of DG18 will help select for the growth of dry-loving fungi that may not grow on MEA agar
- Sampling for Stachybotrys sp. can be achieved with either Cellulose Agar (CA) or Cornmeal Agar (CMA).
- For bacterial sampling, in general, we recommend Tryptic Soy Agar (TSA) or TSA w 5% blood. • For sampling Gram negative bacteria, we recommend MacConkey Agar (MAC)
- For all other situations, the Microbiology Department will be happy to make recommendations based on your individual sampling situation.
- Sampling supplies may be ordered at www.emsl.com or by calling Customer Service: 800-220-3675.
How to Handle Microbiological Media (Agar plates)
- Agar plates must be kept refrigerated or on freezer packs until ready to use.
- The plates must be allowed to warm up to room temperature before taking a sample (approx. 15 minutes).
- Do not remove the lid from the plate at anytime except during sampling.
- Seal the lid to the plate after sample collection with Parafilm or tape.
- The plates must be shipped back to EMSL with freezer packs by OVERNIGHT PRIORITY. Refreeze and reuse the original freezer pack (this type of freezer pack is stable for 24 hours).
- Adequate packing material must be sent to protect the plates.
- Plates must not come into direct contact with the freezer pack, as the media may freeze, invalidating the tests.
- If there is any delay in sending the agar plates to EMSL, they should be refrigerated until ready for overnight delivery.
Recommendations
- Wear latex or nitrile gloves during sampling.
- Use 70% isopropyl alcohol to disinfect sampling device between each sample.
- Place Petri dish lid in a clean bag during sampling to reduce any cross contamination.
- Include outside samples and a field blank for control.
Sampling Procedure
- Allow agar plates to reach room temperature before use.
- Attach one end of tubing to the intake of the vacuum pump and the other end to the inlet of the sampler.
- Calibrate the flow rate of the vacuum pump:
- Place an uncovered Petri dish into sampler (Do not submit this dish as a sample, discard after calibration).
- Turn on pump and adjust flow until the rotameter is at 28.3 LPM (flow rate is read from the middle of bearing on the rotameter).
- Remove stopper and rotameter prior to sampling.
- Wipe all exposed surfaces of sampler with a 70% isopropyl alcohol pad and allow to air dry.
- Place the agar plate on the sampler base so that the Petri dish rests on the three raised metal pins.
- Remove the cover of the Petri dish and place into a clean sample bag to minimize contamination (available upon request).
- Assemble the jet classification stage on the sampler and secure the inlet cone with the three attached clips.
- Set timer to appropriate time depending on environmental conditions (sampling time is usually between 2-5 minutes).
- Turn on the pump and start the timer simultaneously.
- When the time is up, turn off the pump and disassemble sampler and place cover back onto agar plate.
- Secure lid onto Petri dish with masking tape or Parafilm (avoid using electrical, packing, transparent and duct tape).
- Write the sample number on the bottom of the Petri dish.
- Record all appropriate information on the Chain of Custody.
- Return samples with an ice pack to EMSL Analytical for analysis.
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