Legend Technical Services

Microbial Assessment

LEGEND was an environmental prime contractor during the historic Grand Forks Flood Spring 1997 flood giving LEGEND personnel the opportunity to witness first hand what water, particularly dirty water, does to building finishes; effective remediation techniques; how to minimize opportunity for fungal re-growth; and which materials were most resistant to the effects of water.


Evaluating buildings for microbial concerns requires more than collecting air samples, handing over data, and saying “you have mold”.  Fungal organisms are ubiquitous in the outdoor environment aiding decomposition and feeding other organisms.  Fungal organisms produce hardy spores that are a component of environmental dust that enters buildings through foot traffic and ventilation.  If given water, they grow.   Different fungus have different water requirements but will grow under cold conditions; hot conditions; high relative humidity and in damp and saturated materials.   LEGEND works with building owners, facility managers, architects/engineers to identify fungal amplification in a building and control methods.

Technology is constantly advancing, and our techniques change with advancement but sampling techniques include:

AIRBORNE TOTAL SPORE SAMPLING – determined through sampling onto “sticky” slides inside a plastic cassette using a vacuum device with a known air flow.  This method collects particulate/dust and is a measure of both viable (living) and non-viable (dead) spores.  Analysis is by direct microscopy up to 600x with spore division to genus in most cases, provides historical record of fungal growth, and information on hard to culture organisms associated with water intrusion like Stachybotrys sp.

CULTURABLE FUNGAL SAMPLING (AIR AND SURFACE) – Air samples are collected onto various agars using a sieve plate sampler with fine holes to impinge fungal spores across an agar plate.  The agar plate is incubated at a constant room temperature and the organisms detected by microscopic visual analysis of their spores.  Provides information on only living organisms, cultures organisms to species in some cases, and can separate some of the fungal organisms that are too similar to tell apart by total spore sampling.  The limitation of this method is that some fungus don’t readily grow on agar plates.  Surface evaluation is done by transferring surface material directly to the agar plate and treating in the same manner as the air samples.

DIRECT LIFT TAPE ANALYSIS – Clear tape is pressed onto a surface applied to a glass slide and analyzed in the laboratory microscopically in a similar manner to the total spore samples. 

PCR ANALYSIS – polymerase chain reaction applied to fungal and bacterial organisms to identify the fungal organisms present.  Every fungal species has its own-unique, characteristic genetic signature, which varies among species and can provide a genetic fingerprint for their identification.  The power of PCR is to amplify the selected sequence of genetic fingerprint to the level that it can be easily detected and quantified. 


Rapidly, quantitatively, and accurately detects target fungal species regardless of culturability or viability. 


Relatively expensive

Only detect organisms included in the specific PCR package


Available analytical packages:

·         Broad coverage for the 23 most prevalent fungal organisms in water-damaged buildings.

·         Coverage of 15 fungal organisms that are also included in the 23-organism package but less costly.

·         Coverage of 8 fungal organisms most associated with water damage.

·         Coverage of 8 Aspergillus species (Aspergillus species are most known to cause disease in immune compromised people).

·         Coverage of Aspergillus and Penicillium species found in the indoor environment.

·         Coverage of fungus associated with wood dry rot.

·         Coverage of bacterial organisms associated with birds/bats. 

The broad coverage packages are the costliest, however, provide the most information as to presence or absence of one of the included organisms.  Costs can be controlled by targeted composite sampling. 


Multiple techniques are performed to identify the specific organisms being amplified and a causal agent for the amplification.  Fungal levels in outdoor air change seasonally and impact indoor air naturally.  An understanding of the outdoor air is important in interpreting the indoor data.  The identity of the organism(s) present provides information as to the mechanism for water intrusion. 

Strategies are frequently developed during the site visit by observing conditions within the building.


Reports are clear, comprehensive and include the data, methodologies, observations, and a discussion of what was found and recommendations.