Topic of the month: Biocides
By: Dr. Harriet Burge
A question that commonly arises is, “When should I use biocides during fungal remediation in buildings?” Biocides, as the word indicates, are designed to kill living organisms. The simplest answer to the question, is to use biocides when you want to kill something. Answers are never so simplistic, however. Before using a biocide, you should consider the following questions:
- Is killing the organism going to make a difference in the remediation outcome?
- Is the biocide effective against the organisms of concern in this case?
- Is exposure to the biocide more or less dangerous than exposure to the living agent(s) of concern?
The answer to the first question, at least with respect to fungal growth in buildings, is usually “no”. Most illnesses and symptoms related to fungal exposure will occur whether or not the fungus is alive or dead. Also, the use of biocides will only marginally change the speed with which re-growth occurs if suitable moisture conditions recur. Cases where biocides may affect outcomes are in hospitals where infection of immunocompromised patients is of concern, in cleaning up bird droppings infested with Cryptococcus neoformans, or as a delay tactic in areas prone to repeated wetting. Fixing the water problem, or using materials that do not support fungal growth, are better long-term solutions.
The second question is equally important, especially for fungi. Most biocides were designed to kill infectious bacteria in hospitals and other high-risk environments. Many biocides that work well against bacteria are essentially useless for the control of fungi. Thus, fungi are highly resistant to ozone, ultraviolet radiation, quarternary ammonium compounds, and many other commonly used biocides. Some of these biocides (e.g., ozone) will inactivate some spores in a population and enhance germination for those remaining. For this reason, reliance on biocides is not recommended for the control of most fungi. Examples of biocides that are effective against fungi are: ethylene oxide (useful as a fumigant for wet, moldy books), formaldehyde in high concentrations, and glutaraldehyde in high concentrations. None of these are recommended for use except under exceptional circumstances due to their potential toxicity.
For any biocide, it is important to weigh the risks of human exposure to the biocide against the potential benefit of reducing human exposure to the fungal species targeted. For many infectious disease agents for which most biocides were designed, the disease is far worse than exposure to the biocide. So the answer is, for nonspecific building-related symptoms, the risk tradeoff is not so clear-cut.
Conclusion: If possible, biocide use should be avoided. If there is a logical reason to use biocides in a specific case, then care must be taken to insure that the biocide will be effective and that human exposure to the biocide will be minimized.
Fungus of the month: Ulocladium species
By: Dr. Srivandana Kilambi
Ulocladium, a dematiaceous (brown pigmented) filamentous fungi, was first described by Preuss in 1851. PseudoStemphylium is an obsolete synonym for this genus. Ulocladium is considered to be very closely related to Alternaria based upon morphological factors. Ulocladium is considered to be cosmopolitan in the environment and is most often isolated from dead and decaying vegetation, soil, paper, dung, grasses, textiles and air samples. It requires high water content (Aw 0.89) and has an affinity for cellulose. Consequently, it is widespread indoors when there is high moisture and grows on gypsum board, paper, paint, tapestries, jute and other straw materials. Colonies of this fungus grow very well on all general fungal media including MEA. It has dry spores that are generally disseminated by means of wind dispersal.
According to the CABI Bioscience database, 18 species of Ulocladium have been identified, all of which are saprophytes. Spores of Ulocladium are ellipsoidal or obovoid, pale to dark brownish black, smooth or verrucose with transverse and also longitudinal or oblique septa. On spore traps, young spores or fragments may be confused with Alternaria, Pithomyces and other spore types. However, on tape lifts (direct examination) it is distinctive and readily identifiable by the strong geniculate (bent at the points) spore bearing structures.
Various studies regarding indoor air quality in damp and old buildings have revealed that Ulocladium is one of the most frequently encountered among all the micro fungal genera. Studies at the Institute of Hygiene in Belgium have shown that the sites most often contaminated in a house are the kitchen and bathrooms, in which Ulocladium botrytis was most often detected on window frames. The spores were also frequently isolated from bed dust and dust from air conditioners. In burn care units, Ulocladium was the most commonly isolated fungus in the control units.
Ulocladium is known to be a common airway allergen, causing Type I allergies such as hay fever and asthma. Along with Alternaria and Stemphylium, it is considered to be one of the most common mold allergens in the United States. Diagnostic skin prick tests in Riyadh, Saudi Arabia, revealed that 13% of patients with bronchial asthma and allergic rhinitis reacted positively toward Ulocladium fungal extracts, indicating allergic sensitization toward the fungus. It is also known to be a rare cause of subcutaneous infections and phaeohyphomyces (a mycotic infection caused by a dematiaceous conidial mold where the tissue morphology of the causative organism is mycelial) in immuno-compromised patients. Ulocladium’s ability to produce mycotoxins is not clearly known.
- De Hoog, G. S., Guarro, J., Gene, J. and M. J. Figueras. 2000. Atlas of Clinical Fungi. Centraalbureau voor Schimmelcultures, The Netherlands.
- Domsch, K. and W. Gams. 1993. Compendium of Soil Fungi. Vol.1. IHW-Verlag.
- Ellis, M. 1971. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey.
- Ellis, M. and J.P. Ellis. 1998. Microfungi on Miscellaneous Substrates. Richmond Publishing Co. Ltd. Slough.
- Sutton, D. A., A. Fothergill, and M. Rinaldi. 1998. Guide to Clinically Significant Fungi. Williams & Wilkins, Baltimore.
- www.ncbi.nlm.nih.gov - Pubmed
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