Home > Mold, Microbes > Non Culturable Bioaerosol Sampling (Spore-Trap)

Let us begin by defining "Non-Viable" and "Viable". Non-viable refers to techniques that identify fungal spores or conidiophores without any attempt to culture the spores. It does not infer that the spores are not capable of germination or growth. Viable techniques are an attempt to recover either fungal spores or bacterial cells in the environment from which they were collected. For the purpose of this discussion, non-viable would refer to the microscopic examination of spore trap, tape, bulk or swab samples. Viable would include the collection and growth of fungal spores or bacterial cells on agar plates or dilution plate culturing of fungal or bacterial cells from swab, bulk or dust samples.

Burkard spore trap sampling is a non-culture based tool that provides a snapshot of the kinds and levels of total (viable and non-viable) airborne fungal (mold) spores present in the indoor environment. Direct microscopy is used to analyze Burkard samples, providing both a qualitative and quantitative assessment of spores in the air in a short timeframe. Air sampling is used to determine whether the mixture of airborne fungi in a building is normal and typical or indicative of moisture problems. Air sampling is also an important tool for conducting exposure assessments. Burkard sampling provides a quicker turnaround time than culture-based analysis, when rapid communication of results is essential. Often investigators use non-culturable air sampling as post-remediation clearance testing to evaluate effectiveness.

This method provides report on both raw spore counts for individual spore types and total concentration expressed as particles per cubic meter (particles/m3). The proportions of each spore type are also calculated and important groupings of fungal types are summarized to facilitate interpretation of results. We can also include qualitative data on pollen and skin scales for each sample.

Burkard spore trap sampling is a device designed for the rapid collection and analysis of a wide range or airborne aerosols. These include fungal spores, pollen, skin cell fragments, fibers and inorganic particulates. Air enters the cassette, the particles become impacted on the sampling substrate, and the air leaves through the exit orifice. The airflow and patented cassette housing is designed in such a way that the particles are distributed and deposited equally on a special glass slide contained in the cassette housing.

Advantages of this technique are:

• Useful for initial site testing, especially if fungal growth is not visible
• Provide rapid delivery of total spore counts and types in air samples
• Easy to use and handle in the field
• Provides a convenient analysis to identify and enumerate spores and structures without the additional time required to culture fungal samples

Disadvantages of this technique are:

• Fungi cannot be fully speciated with this method. For example, Aspergillus sp and Penicillium sp are normally reported together due to the similarities in spore morphology.
• Spore viability cannot be assessed, as it is not possible to differentiate between viable and non viable spores.

Burkard Sampler

Burkard slide shows Curvularia Spore

 

Swab Samples

Swab sampling in IAQ investigation is usually done in combination with other methods, such as air and bulk sampling. It is normally done when the surface is a non-porous (smooth) material, and cutting it is undesirable or not an option (countertops, poles, floors, etc.). The analysis of surface samples can provide information about whether a suspect area is supporting microbial growth as a potential source of biological agents in the air. In addition, settled spores can be determined on surfaces. Surface samples can be analyzed to semi-quantify and identify organisms by direct microscopy, and/or culture methods.

With a moist sterile swab, swab the desired area (1 to 100 cm2 surface horizontally and then vertically to cover the entire area.) thoroughly with a rolling motion to allow a sufficient amount of material to accumulate on the swab tip. Place swab in corresponding tube (zip lock bag are OK), and make sure it is completely sealed.  The swab is labeled in conjunction with the sample number and information on the COC form. Samples are perishable and should be shipped via overnight courier to the laboratory. Samples requiring enumeration of bacteria or yeasts should be shipped in an insulated cooler with cold pack to avoid growth in transit.

Picture shows mold growth on the Ceiling board

Bulk Samples

Bulk samples are portions of materials (e.g., pieces of wallboard, duct lining, carpet, insulation etc.) that are tested to determine if they may contain, or be contaminated with, microbial agents. Analysis of bulk samples can provide information regarding possible sources of microbes and their toxins, allergens, and irritants. These analyses can also provide information on the effectiveness of the remediation process.

Obtain a piece (or pieces) of the desired material to be tested, and place them individually in sealable plastic bags (Ziplock bags work very well). Water samples should be collected in tightly sealing, sterile, plastic containers. The sample is labeled in conjunction with the sample number and record on the COC form, the type of test required. The package should be shipped via overnight courier. Wet samples should be transported in insulated coolers with cold packs to prevent proliferation of organisms during transit.

Dust Samples

Dust samples can be analyzed by direct microscopy, but they are best analyzed by culture-based methods.

Settled dust can be collected directly from hard surfaces or extracted from carpeting and other porous surfaces (example: furniture, clothing, books and papers) using a 0.45 µm methyl cellulose ester (MCE) filter dust cassette and collected with a vacuum pump. The blue plug is the inlet, and the red plug is the outlet. Remove both plugs of the cassette and connect the outlet to the pump via 2 feet of plastic tubing.

Although the samples may be collected for a variable length of time and over a variable area in accordance with the desired sampling goal and dust content of the surface being sampled, a standard pattern of collection helps to provide uniformity and comparability in sample results. For example, to collect carpet dust, go to a low traffic area and sample using a standard time, flow rate, and surface area (example: 2 min., 28.3lpm, I sq.ft.), while brushing the sampler inlet across the surface of the carpet in a horizontal and then vertical pattern. After sampling is completed, replace the caps over the cassette inlet and outlet. The results can be reported on a weight basis as colony-forming units per gram of dust (cfu/g) or, if the sample areas are known to the laboratory, on an area basis as cfu/cm2 or cfu/100 cm². The cassette is labeled in conjunction with the sample number and information on the COC form. Samples will not deteriorate in transit and may be shipped to the laboratory at your convenience. No refrigeration is needed.

Tape-lift Sample

Tape lift sampling method is the quickest and most cost effective to confirm the existence of mold growth, and to identify the type of fungi at the sampling site. Tape-lift sampling is best used in conjunction with air sampling for verification of indoor mold growth by direct fungal examination.

Take a piece of Scotch transparent tape about 1-2 inches long. Fold one end over to provide a ‘handle’ and apply the sticky side to the target site, gently press the middle portion of the tape to sample an area of 1 cm2 to 1 in2,, and lift the tape. Do not fold the tape itself, but rather, mount it on a glass microscopic slide (ensure slides are adequately protected to prevent breakage in transport). Clearly label the slide with sample number and information on the COC form and shipped at room temperature to the laboratory.

Compared with swab sampling, tape-lift sampling has the following advantages:

• Better preservation of fungal structure, which may allow for identification of higher resolution.
• Does not permit fungal spore germination and yeast reproduction during storing and shipping.

However, tape-lift samples are not suitable for culturable analysis.

Tape lift sample shows Aspergillus/Penicillium spores under the microscope




Tape lift sample shows conidiophore of Aspergillus sp. under the microscope

Read more about Outdoor Mold Assessment as a Background Control