DETECTION OF FUNGAL GROWTH

Abstract: A method of detecting viability in fungal cells from fungi infected buildings or building materials, according to which a sample is taken out and examined for the presence of fungal cells containing cell nuclei with chromosomes, which is detected by means of nucleus dyeing techniques comprising e.g. DAPI fluorescence dyeing.

Description: Detection of Fungal Growth 1. THE TECHNICAL FIELD The present invention relates to a method of detecting the viability of fungal cells from fungi infected build¬ ings or building materials. Detection and assessment of the extent of damage to build¬ ings or building materials in connection with controlling fungal infections may today be performed by various tech¬ niques including destructive sampling as well as physic¬ ally non-destructive measuring methods. In order to effectively control a fungal infection it is important to know in advance precisely where the fungal attack is located, whether the fungus is alive and if so the required duration and extent of the treatment of the fungus. This is so because in case of older dry fungal infections it is a natural thing that only parts of the fungus are viable, and consequently the repairs of the building may often be limited to the growth zone or may be completely avoided in case of long dead fungi in con- struction materials with otherwise intact strength pro¬ perties. Because of the uncertainty related to the via¬ bility of the heat treated fungus, the repairs are often extended to include a safety zone, the repair of which further adds to the costs, and may in certain cases be avoided if the viability of the fungus could be ascertain¬ ed. Furthermore, it is today difficult to determine at which temperature and for how long a given fungal treatment by means of e.g. heat treatment must be carried out using e.g. a microwave canon in order to obtain or assist in obtaining efficient and reliable control of the fungus. When treating and repairing fungal infections, it is therefore important to have at one's disposal a simple method of detecting the viability of fungal cells in buildings or building materials. 2. BACKGROUND ART Until now the method used in practice for detecting the viability of fungal cells from fungi infected buildings or building materials has been collecting samples from infected buildings or building materials and transporting the samples to a well equipped biological laboratory, where the samples are grown on suitable substrates. According to known techniques it is attempted to revive the fungus under optimum conditions, including inoculation on growth substrate and 2-6 months in culturing chamber, whereafter, typically not until after 6 months of un- successful reviving attempts, it is considered reasonably likely that the fungus in non-viable. Culturing on substrates containing malt extract and agar, S. Cymorek and B. Hegarty, Int., Res. Groups Wood Pres., Doc. No. IRG/WP/2255, 1986, is an example of simple culturing of e.g. dry rot. It is a significant drawback of culturing fungal cells as a test of viability that the method is time consuming. Incubation periods of 2 months or more are often recommended in which period a fungal infection may have grown to an extent which is almost irreparable. It has thus been ascertained that the fungus under favourable conditions may spread at a rate of approx 0.5 cm in 24 h and grow as high as a 4 storage building. Furthermore growth of other fungi may often conceal the growth of the fungus which it is desired to detect, i.e. lack of growth of the interesting fungus in the test culturing may both be due to the fungus being dead or to unsuccessful attempts to revive it from its dormant state. Revival by simple culturing is thus a slow and uncertain method of detecting viability. 3. DISCLOSURE OF THE INVENTION It is the object of the invention to devise a fast, un¬ complicated and simple method of detecting the viability of fungal cells from fungi infected buildings or building materials. Another object of the invention is to provide a method that may be performed directly at the infected buildings or building materials without the necessity of transfer- ring samples to a laboratory. A further object of the invention is to perform a determination for viability very fast, e.g. within a few hours or less, on the spot and with very simple equipment. According to the invention a fast, uncomplicated and simple method may consist in detecting whether the samples taken from fungi infected buldings or building materials comprise fungal cells containing cell nuclei having chromosomes. Accordingly, in its broadest aspect the present invention is characterized by a sample being taken out from the building or building material and examined for the presence of fungal cells containing cell nuclei having chromosomes by subjecting the sample to a treatment with a substance containing a cell nucleus chromosome marker and subsequently detecting the marked cell nucleus chromosome. The method according to the invention is further charac- terized by the cell nucleus chromosome marker containing substance being a dye which is used for dyeing the chromo¬ somes in the cells in a manner known per se. Although it is known to dye the DNA, deoxyribonucleic acid, of the chromosomes in connection with cellular structure examinations and the like, no so-called nucleus dyeing methods have until now been provided in connection with detection of the viability of fungal cells from fungi infected buildings or building materials. In a preferred embodiment of the invention the method is further characterized in that the cell nucleus chromosome marker containing substance is a DNA-dye, i.e. a substance which dyes DNA, a fluorescent DNA-dye or another detect- able cell nucleus chromosome marker substance, and that the detection is performed by means of light or fluor¬ escence microscopy, respectively, or by another detection method. Known fluorescence dyes, such as bis-amino-phenyl- oxadiazol, acriflavin, pararosanilin, bis-benzimide (Hoechst 33258) and 4' ,6-diamino-2-phenyl-indol, DAPI, are examples of fluorescence dyes which dye DNA and which are usable for dying chromosomes according to the invention. Such dyes have been used for detecting chromosomes and cell nuclei for different purposes. Examples of further typical DNA fluorescence dyes are propidium iodide, ethidium bromide, dihydroethidium, ethidium monoazide, 9-azidoacridine, ethidium homodimer (5,5'-diazadecamethylene)bis(3,8-diamino-6-phenylphen- anthridium) dichloride, acridine-ethidium heterodimer, acridine homodimer (bis-(6-chloro-2-methoxy-9-acridinyl) spermine), acridine orange, Hoechst 33342, 7-amino- actinomycin D, thiazole orange, 9-amino-6-chloro-2- methoxyacridine, 4,5' ,8-trimethylpsoralen, and Malachite Green acrylamide. Other useful dyes may be selected by a person skilled in the art. A known method of nucleus dyeing according to which the DNA of the chromosomes is dyed by means of basic fuchin, is the reference method by Feulgen, see e.g. Laurits W. Olson, Opera Botanica, No. 73, 1984, p. 65-66. Another method is the DAPI-nucleus dyeing method according to which the fluorescence dye 4' ,6-diamino-2-phenylindol, DAPI, is used for dyeing chromosome DNA which subsequently exhibits a blue or bluish colour in the fluorescence microscope. The method has been used for detecting nuclei in spores from dry rot cultivated in laboratory cultures with the purpose of examining the structure and germina¬ tion of basidiospores, B. Hegarty and U. Schmitt Int. Res. Group. Wood Preservation, 19. Annual Meeting, Madrid, Spain 24-29 April 1988. Use of the DAPI dyeing method in these examinations however does not concern detection of viability within the meaning of the present invention, neither as regards spores nor fungal cells. In a preferred embodiment of the invention the metod is characterized in that the fluorescent DNA-dye for dyeing the chromosomes is 4' ,6-diamino-2-phenylindol, DAPI, in a concentration of preferably 1-5 ug/ml. Field and laboratory tests performed have shown that the procedures used for fixing the sampled material may advantageously be adapted to the treatment method. It is generally believed that the sampled cell material must be fixed immediately after the sampling in order to preserve the sample for later laboratory analysis. If this preservation is not performed the cells easily become overgrown by other organisms, in particular if the fungal cells are dead, whereby the samples are ruined and the risk of misinterpretation of the viability of the sampled specimens increased. By employing traditional fixation of the sample immediately following e.g. a lethal microwave radiation it has turned out that the chromosomes in the nuclei have not yet disappeared and consequently get fixed "too early", wherefore in the microscopy well preserved nuclei can be detected in cells which in fact are dead. It has thus been possible to detect chromosome material in cell nuclei 1 h after mycelium from actively growing dry rot has been boiled for approx. 4 min. When fixing after 24 h the nucleus material has disappeared. Consequently, it has proved expedient to dry and option¬ ally freeze dry the sampled test material, in particular for samples taken out after heat exposure, whereafter they are kept dry until fixation and microscoping. In connection with the microscoping it has further proved expedient to separate the hyphae in such a way that the test becomes simple and uncomplicated. In a preferred embodiment of the invention the method is thus characterized in that the sample optionally is pre- treated by drying or freeze drying whereafter it is kept dry in a storage period before it is fixed and/or option¬ ally posttreated to separate hyphae. Thus the sample is not fixed immediately upon sampling, which ensures that the chromosome material in the nuclei of non-viable cells disappears before fixation and micro¬ scoping whereby the risk of misinterpreting dead cells as viable cells is reduced. Advantageously the storage period is adjusted to the treatment method and may in case of heat exposed fungal myceliae be as long as 48 h, however preferably 24 h, shorter periods however being possible. Optimum periods are easily adjusted according to the treatment method, the exposure effect and the exposure time. The fixing agent is advantageously selected in view of the treatment method and the test material. In a preferred embodiment the fixing agent perferably comprises ethanol/glacial acetic acid mixtures in the preferred ratio 3:1. Besides employing a posttreatment of the fixed and dyed sample to separate the hyphae, which in a preferred embodiment comprises preferably mechanical pulverization, it has proved expedient to increase the specific DAPI- absorption of the chromosomae DNA in e.g. dry rot by adding a detergent solution. Useful detergent solutions include known detergents preferably Triton 100-X and various detergent concentrations, preferably 5 %. Consequently the method according to the invention is further characterized in that the cell nucleus chromosome marker containing substance is dissolved in a detergent solution, preferably approx. 5% Triton 100-X. Within the meaning of the invention viability designates the capability of the fungal cells to reproduce themselves so that the fungal cells may propagate and the myceliae spread to the surrounding buildings and building materials . According to the invention it is not sufficient that the fungal cells are capable of metabolizing, as fungi under certain conditions especially of low humidity may enter a sort of "dormant state", in which their metabolic process act very slowly. In dependence on the kind of fungus the dormant state may last 2-10 years before the fungal cell dies, wherefore the fungal cells are still viable and may be revived under suitable conditions of growth. Viable cells within the meaning of the invention however all comprise a nucleus with chromosomes which enable the cell to reproduce itself. When a fungal cell is no longer viable in the meaning of the invention the chromosomes of the cell nucleus disappear and the cell is no longer caple of reproducing itself. Fungal cells having a cell nucleus with chromosomes will thus either be viable cells in the form of active cells capable of reproducing themselves or of cells in a dormant state, or be non-viable cells, the chromosomes of which in the nucleus have not yet been dissolved. In the absence of cell nucleus containing chromosomes the fungal cells are no longer viable within the meaning of the invention. Fungi according to the invention include , Serpula lacrymans, Coniophora putana, Antrodia sp., Gloeophyllum trabeum, etc. and other fungi capable of infecting buildings and building materials. According to the invention samples of buildings or building materials include thallus, mycelium, hyphae, unit cells or spores of the fungus. Buildings or building materials in the meaning of the invention comprise all materials which form part of or may form part of buildings and building constructions which the fungus may infect no matter whether it e.g. means the end of the life of the building material. 4. BRIEF DESCRIPTION OF DRAWINGS In the following the method according to the invention is described in more detail, reference being made to the drawings in which fig. 1 shows the presence of cell nucleus chromosome containing fungal hyphae as detected by means of the Feulgen nucleus dyeing method and floures- cence microscopy, fig. 2 shows the presence of cell nucleus containing viable fungal hyphae in a dormant state as detected by means of the DAPI nucleus dyeing method and fluorescence microscopy according to the invention, and fig. 3 shows non-viable fungal hyphae without chromosome containing cell nuclei from mycelium having been boiled for 4 min and fixed after 24 h and measured by means of the DAPI nuclei dyeing method and fluorescence microscopy according to the invention. 5. DETAILED DESCRIPTION A particularly preferred embodiment of the method according to the invention comprises the steps of 1. fixing the optionally pretreated sample in an ethanol/glacial acetic acid mixture preferably in the ratio 3 : 1 , 2. washing the sample in destilled water, 3. dyeing the sample for approx. 5 min-2 h preferably with a 2% mixture of the fluorescence dye DAPI (Sigma) in an acetone basis solution yielding a final concentration of l-5ug/ml, and a 5% Triton 100-X detergent solution, 4. washing the sample in destilled water, 5. optionally crushing the sample to separate the individual hyphae by means of a coverglass and a drop of water, and 6. microscoping the sample by means of fluorescence microscopy at 1000 x enlargement using a mercury lampe, 365-366 nm, filter, 40-100 x objective and oil immersion. 6. EXAMPLES The method according to the invention has been used for detecting the viability of fungal cells in both live and dead mycelium from dry rot. Live myceliae have been cultured non-sterilized from fungi infected wood, stone wool and bridgework, i.e. mortar and bricks, in the laboratory, whereafter they have been tested for asensitivity to the dyes. Dead mycelium has been provided by heat treating the live mycelium in a microwave oven and by boiling for e.g. approx. 4-10 min, respectively. Old presumably inactive mycelium has also been provided. In all cases the method has been satisfactory. EXAMPLE 1 To illustrate the method according to the invention the Feulgen nucleus dyeing method has been used on samples of live mycelium from dry rot. Fig. 1 shows fluorescence microscopy of fungal hyphae from live mycelium of dry rot having been dyed by means of the Feulgen-dyeing method. The arrow in the centre of the picture refers to a nucleus which in a colour picture shows itsels as dark red approaching violet on a reddish background. Is appears that the Feulgen dyeing method which usually dyes the chromosomes in the nuclei a bright reddish only dyes fungal myceliae faintly. This is probably due to the chitin content of the cell wall and the scarce amount of chromosomes present in the cell nuclei. Besides being an extremely time consuming preparation where certain steps in the procedure may easily go wrong the method calls for use of phase contrast microscopy to make possible nuclei detectable. Consequently, the method is less advantageous for use when carrying out the procedure according to the invention. EXAMPLE 2 To illustrate the method according to the invention the DAPI nucleus dyeing method has been used on the previously mentioned live and dead mycelium from dry rot. Fig. 2 shows fluorescence microscopy of viable fungal hyphae in a dormant state. In the picture the nuclei dyed bright blue appear as white spots in the more dim contours of the fungal hyphae. In comparison with the Feulgen nucleus dyeing method the DAPI method is far more practical in use. EKXAMPLE 3 Fig. 3 shows fluorescence microscopy of non-viable fungal hyphae from mycelium having been boiled for 4 min and fixed 24 h later on whereafter they have been dyed by means of the DAPI nucleus dyeing method. The picture clearly shows the absence of dyed nuclei.

Claims: P a t e n t C l a i m s: 1. A method of detecting the viability of fungal cells from fungi infected buildings or building materials, c h a r a c t e r i z e d in that a sample from the buildings or the building material is subjected to a treatment with a substance containing a cell nucleus chromosome marker whereafter the marked cell nucleus chromosome is detected. 2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the cell nucleus chromosome marker containing substance is a dye being used for dyeing the chromosomes in the cells in a manner known per se. 3. A method according to claims 1-2, c h a r a c t e r ¬ i z e d in that the dye for dyeing the chromosomes is a fluorescent DNA-dye, preferably 4' ,6-diamino-2-phenyl- indol, DAPI, in a concentration of 1-5 ug/ml. 4. A method according to claims 1-3, c h a r a c t e r ¬ i z e d in that the substance containing the cell nucleus chromosome marker is dissolved in a detergent solution, preferably an approx 5% Triton 100-X. 5. A method according to claims 1-4, c h a r a c t e r ¬ i z e d in that the sample is pretreated by drying or freeze drying whereafter it is kept dry for a storage period lasting as long as 48 h, preferably 24 h, fixed and optionally posttreated to separate hyphae. 6. A method according to claims 1-5, c h a r a c t e r ¬ i z e d in that the sample is fixed by a fixing agent, preferably a 3:1 ethanol/glacial acetic acid. 7. A method according to the claims 1-6, c h a r a c ¬ t e r i z e d in that the sample is posttreated to separate hyphae preferably by mechanical pulverization.

Inventors: MUNCH OLE, SUNDBERG HENRIK, MUNCH, OLE, SUNDBERG, HENRIK
Applicants: ASSURANCE COMPAGNIET BALTICA A, ASSURANCE-COMPAGNIET BALTICA A/S
Application year: 1990
Main classification: G01N33
IPC codes: C12Q1, G01N33