Indoor Air Sampling Information for Professionals
There are several concerns in evaluating indoor environments.
Those that are viable and those that add to the respiratory load (but may not be viable or microbial).
- Viable counts
- - Used as measure of respiratory load that will continuously be added to the environment.
- - Used as an indication of building or hygiene problems ie elevated bacterial numbers generally indicate the presence of a wet environment often preceding fungal contamination
- - Evaluation of the effectiveness of a sanitation protocol
- - May be used to identify organisms to genus & species (pathogenic, cultural characteristic –ie prolific spore production, odor, environment & habitat requirements useful to pinpoint locations or conditions)
- - Used as a measure of respiratory load. Often done as a total particulate count or as a viable/non-viable estimate of sanitation efficacy
- Chemical contaminants
In many cases can still be counted from agar based collection systems. This does however, require that the laboratory routinely reads all plates with an appropriate microscope & optics. If the field specialist is concerned with non-viable particles, it would be advisable to collect a dust or particulate sample while onsite.
The professional should ask the laboratory for a selection of media for a given collection device. Agar plates, strips and liquids are available in many formulations. PDA, TGEA and CD are a common combination. NOTE: PDA medium with rose bengal is extremely restrictive (or toxic) to most fungi including Fusarium spp. Fast Growing Fungi – using a multiple media approach often mediates this problem. A competent mycology laboratory will be monitoring and counting colony centers within 24 hours of incubation. Heavily overload samples (ie inappropriate sampling device) or sampling media not submitted in a timely fashion are the most likely causes for “overgrown” results.
Seasonal & Daily Weather Conditions
Will definitely have a significant influence on yield. In fact, many fungi respond to environmental triggers such as light (turning on lights in an office) or rapid fluctuations in humidity or temperature such as turning on an air conditioner or opening a door. Daily human activities can have a dramatic influence on spore release. A competent field professional will be aware of these potential conditions. Conducting a thorough verbal questioning of the people using the space(s) as well as careful site evaluations and sampling will be key elements in a successful investigation. Some sites will require multiple sampling to monitor seasonal variation or to verify that remediation has been successful.
Stachybotrys is a group of fungi that are typically found associated with cellulitic plant material and soil. There is more than one species in the genus, however all are classified as potential pathogens of humans. The fungi belonging to this genus plus the closely related genera Memnoniella and Hyalostachybotrys produce a series of mycotoxins (macrocyclic trichothecenes, satratoxins & phenylspirodrimanes) that are cytotoxic and immuno-suppressant. These toxins are the pathogenic element. The toxins are present in the mycelia, spores & slime. It is thought that the biological function is to suppress competition of other microbes. Many of the toxins are volatile.
Stachybotrys spp produce spores in a slime covering. The conidia are spread primarily from contact and soil not through air dissemination. The organism is found in indoor environments that are wet/moist and dark such as behind wallboard, backsides of toilet cisterns etc. It is unusual to find Stachybotrys spp in air samples (regardless of the collection apparatus), even if indoor spaces are heavily infested.
All species of Stachybotrys will grow readily in a number of media including rice, cornmeal, czapex dox, potato dextrose and malt agars. The task of a competent professional is to examine both the air quality, ventilation AND the indoor surfaces for potential problems. In most cases, Stachybotrys is isolated and confirmed from bulk samples such as scrapings, swabs or pieces of building materials rather than an active or passive air sampling device.
- Stachybotrys atra Corda (S. chartarum)
- Stachybotrys atra var microspora Math&Sank
- Stachybotrys bisbyi Jensen
- Stachybotrys chartarum (atra) Corda
- Stachybotrys cylindrospora Jensen
- Stachybotrys dichroa Grove
- Stachybotrys parvispora Hughes
- Stachybotrys scabra Cooke & Harkin
Author: Dr. H. Hartmann, Mycology Section - Microbiology Department