Viable and Non-Viable Mold Spore Analysis Our laboratory conducts both viable and non-viable spore testing and provides non-viable spore traps to assit you in determining the presence of mold.  Please review the below to determine which testing procedure is best for you. For more information, please complete our Request Form on the right hand tool bar. Viable versus Non-Viable Mold Spore Testing   General cases   In general, techniques of investigative mould sampling are divided into two main categories, which indicate two very different approaches to the problem of finding out what is there and what it might be doing. These are called ‘viable’ and ‘non-viable’ sampling methods. To begin with, I must warn you that both descriptors are extremely misleading.   First, the term ‘viable’ is used in the aerobiological context to describe propagules (whether spores, spore-bearing structures or hyphal fragments) which will germinate and grow on some common laboratory media (and sometimes, by extension, inside people whose immune systems are deficient or compromised). These propagules are often collected by drawing air onto the surface of a plate (Petri dish) containing a solid nutritive medium. The assumption seems to be that whatever is not a ‘cfu’ (colony forming unit) under these conditions either does not count or does not exist for the purposes of the investigation. This contention is easy to refute. Many of the fungi whose propagules are often found in air samples are obligately biotrophic (they will grow only on or in a living host). These include such common members of the aeromycota as rust fungi (Uredinales, Basidiomycetes), powdery mildew fungi (Erysiphales, Ascomycetes), and downy mildew fungi (Peronosporales, Oomycota). Even if the spores of these taxa were to germinate, they would be unable to acquire necessary nutrients, would be unable to establish visible colonies or mycelia, and would soon die. In addition, there are many other kinds of spore, such as those of some puffballs, which have a vanishingly small rate of germination even under the most congenial conditions, and the basidiospores of many other basidiomycetes require specialized media not usually employed in air sampling exercises. In addition to the living spores that will not grow in culture, many of the spores in the aeromycota - about half of the total - are in fact dead.   It is clear, then, that the so-called ‘viable’ methods will detect only a fraction of the spores in the air that are actually viable, that many of the visually identifiable spores in the air are actually non-viable, and that the results of such methods, unsupported by other approaches, is bound to be misleading.   Now let’s turn to the so-called ‘non-viable’ methods. This inaccurate descriptor makes it sound as if we are detecting things that wouldn’t germinate, even if we gave them something suitable to grow on. These ‘non-viable’ methods include such techniques as quantitative spore sampling using one of a variety of spore traps (e.g. AeroTrap AllergencoD), and tape lifts (pressing a piece of transparent adhesive tape against a substrate and subsequently examining it under the microscope). In each case moulds are identified visually under the microscope, and no attempt is made to germinate or culture them. The truth is that many of the spores picked up by these techniques are perfectly viable, and would definitely grow if given the chance. The chief drawback of this approach is that it is impossible to identify many kinds of spores with precision when they are seen in isolation.   Which kind of sampling is to be preferred? Well, if you really want to know what is in the air, you will have to take quantitative ‘non-viable’ air samples. It has been repeatedly demonstrated that spore counts can vary dramatically from one time of day to another, with changes in the weather, and with the amount of traffic or disturbance going on.   It is also known that most spores inside buildings usually originate outside, so repetitive samples will have to be taken at different locations both inside and outside the building. This is an expensive and time-consuming process (since it also takes considerable time to ‘read’ such samples, and the problems of identification are considerable). However, it is sometimes necessary, because it is the only way in which we can determine what people are actually inhaling, qualitatively and quantitatively. If you want to know which fungi are, or have been, growing in the building, your best bet is tape lifts. All you have to do is prepare short lengths of clear adhesive cellulose tape, with one end of the adhesive side turned back on itself to make a ‘handle’. You find the areas on which mould is present, and press the tapes against the various surfaces. Then each tape is pressed onto a regular microscope slide and put in a ziploc bag or slide box for transportation back to the lab. To facilitate microscopic examination most of the tape is peeled back and a drop of mountant (e.g., lactic acid) is interpolated between tape and slide. Then another drop is placed on top of the tape, and a coverslip put in place. The slide is gently heated to drive out air bubbles, and then scanned. Tape lifts are not precisely quantitative, but they have the important advantage that the several parts of the fungi (e.g., hyphae, conidiophores, conidiogenous cells, conidia) often stick to the tape while retaining their original orientation to each other. This enables the reader to make a much more precise determination of the fungi than would be possible if only the spores were present (as is usually the case in air samples). It also enables the reader to see what state the fungi are in, if they are mixed together, and whether there is also arthropod frass (excreta) or arthropod or worm carcasses present. This permits a more forensic approach to reading the slide. In terms of allergenic potential, it does not matter whether a spore is alive or dead - the allergens are present in either case.   Special cases   But there are situations in which it matters whether the spores are alive. These are: (1) in hospitals, where patients may be either immunocompromised, or immunosuppressed as a result of their medical condition or their treatment, or (2) in the homes of immunodefi cient people. In those cases, mould spores belonging to thermotolerant or opportunistic species may be able to establish themselves within the patient and lead to serious illness and even death. In addition, there are several situations in which ‘viable’ and ‘non-viable’ methods can be truly complementary. (1) Perhaps the most important is the ability of culturing to resolve Penicillium from Aspergillus, and to be precise about the species involved. Identification of, for example, Aspergillus fumigatus (which can cause disease in humans), may be very important. (2) If spores in samples are proven to be viable, at least some of those spores may remain viable for an extended period, and can affect future sampling. (3) Certain kinds of spores, especially those which are small and colourless, are often difficult or impossible to identify visually: high counts of such spores in a spore trap may correlate with a large number of, for example, Beauveria colonies in culture. (4) In some situations it may be helpful to know which species of a particular genus are present inside and outside a building. For example, we might be inclined to ignore an apparently trivial difference between spore trap counts of Cladosporium outside and inside. But knowledge that the external spores were of C. cladosporioides, and those indoors of C. sphaerospermum, would be highly signifi cant. It is clear, therefore, that both ‘viable’ and ‘non-viable’ methodologies are valuable.   News Update: Benchmark Labs scored 90% in its last 2 non-viable spore performance tests with the American Industrial Hygene Association (AIHA)!