In eastern Europe, in the 1930s, outbreaks of a disease of horses and other animals that was characterized by symptoms such as irritation of the mouth, throat, and nose; shock; dermal necrosis; a decrease in leukocytes; hemorrhage; nervous disorder; and death were associated with Stachybotrys chartarum (then known as S. alternans) present in straw and grain fed to the horses.

Currently, health effects in humans attributed to Stachybotrys chartarum, are controversial. However, it is generally agreed that Stachybotrys chartarum can potentially cause allergic reactions from inhaled spores and also poses the threat of mycotoxin poisoning.

One of the disputed claims is the association of Stachybotrys with the idiopathic pulmonary hemorrhage that resulted in deaths of infants in Cleveland, Ohio, USA, in 1993-1994. After a review of the reports, the US Centers for Disease Control and Prevention (CDC) concluded that a possible association between pulmonary hemorrhage in infants and exposure to molds, specifically Stachybotrys chartarum, was not proven.

Spores of Stachybotrys are believed to contain high concentrations of mycotoxins. Therefore, inhaling large numbers of these spores potentially can cause mycotoxin poisoning. Luckily, spores of Stachybotrys are not readily disseminated in the air, primarily because they usually occur in a cluster covered with wet slime. Therefore, exposure to huge amounts of airborne Stachybotrys spores would only occur when the spores dry out and are disturbed, for example, during renovations.

Black Mold (Stachybotrys) as a New Emerging Opportunistic Human Fungal Pathogen

Recently, Stachybotrys chlorohalonata, was isolated from the sinuses of a patient. This is the first reported case of invasive Stachybotrys chlorohalonata sinusitis. The patient was cured from this infection after sinus surgery and antifungal treatment.

S. chlorohalonata is very closely related to S. chartarum. It differs morphologically from S. chartarum by having smooth spores, and having more restricted growth on lab media.

The general public thinks that black indoor molds are toxigenic because of the publicity that Stachybotrys chartarum (a.k.a Stachybotrys atra in the old literature), a black mold, received in the recent years. However, the colour of the indoor molds does not determine whether they are toxigenic or not.

Growth of indoor molds on building materials is determined by the water activity (a_w) among other factors. The a_w is a measure of the moistness of the material. Some indoor molds are capable of growing over a wide range of a_w but there is always an optimal range.

Common Indoor Molds

The indoor molds commonly found on building materials are discussed below.

Stachybotrys chartarum

Stachybotrys chartarum is cosmopolitan and grows naturally on straw and other cellulose containing materials in soil. In the indoor environment, this mold is commonly found together with Stachybotrys chlorohalonata on cellulose containing materials including paper, canvas and jute which are wetted to a water activity > 0.98.

In a study on indoor molds conducted in Denmark, Stachybotrys chartarum was found to produce a number of mycotoxins including macrocyclic trichothecenes, satratoxins and roridins when growing on building materials. However, only 35% of the isolates from buildings produced the extremely cytotoxic mycotoxins, the satratoxins.

This led to the conclusion that idiopathic pulmonary hemosiderosis in infants is possibly not caused by satratoxins but by other S. chartarum mycotoxins.The optimum temperature for growth for Stachybotrys chartarum is 23 ^oC with a minimum and maximum temperature of 2 and 37 ^oC respectively.

The optimal water activity is 0.98 with a minimum of 0.89. To read more about Stachybotrys chartarum and S. chlorohalonata click here.

Aspergillus flavus

Aspergillus flavus is widely distributed in soil. It is associated with a wide range of stored products such as maize and nuts. In indoor environment it is commonly found on damp walls, wallpaper, floor and carpet dust, tarred wooden flooring, humidifiers and HVAC fans, bakeries, shoes, leather, and bird droppings. Strains of this mould may produce aflatoxin, a class 1 carcinogen.

The minimum and maximum temperature for growth are 6 and 45 ^oC, with an optimum at 40 ^oC. The minimum water activity is 0.78 and an optimum at 0.98.

Aspergillus fumigatus

Aspergillus fumigatus is common in composting plant material, woodchips and garbage. Also common in dust infiltrating from outdoor air, carpet and mattress dust, wet building and finishing material, HVAC insulations, fans, filters, humidifier water and potted plant soil. A. fumigatus is a producer of various mycotoxins including gliotoxin, verrucologen, fumitremorgin A & B and fumigaclavines among others. A. fumigatus has an optimum growth temperature at 43 ^oC and minimum and maximum at 10 and 57 ^oC respectively. Minimum water activity is 0.82 and an optimum at 0.97.

Aspergillus niger

Aspergillus niger is found worldwide in soil and plant litter. In indoor environment A. niger is common in floor, carpet and mattress dust, acrylic paint, UFFI, leather, HVAC filters and fans, and potted plant soil. A. niger produces malformins and a few strains also produce ochratoxin A. A. niger requires a minimum temperature for growth at 6 and maximum at 47 ^oC with an optimum at 37 ^oC.

Aspergillus versicolor

Aspergillus versicolor is one of the common indoor molds. It is very common on gypsum board, floor, carpet, mattress and upholstered-furniture dust, and damp walls. A. versicolor produces high quantities of the carcinogenic mycotoxin, sterigmatocystin at water activities (a_w) above 0.95. A. versicolor is generally xerophilic- meaning that it can grow at low water activity (<0.80). The minimum and maximum growth temperatures for A. versicolor(/i> are 4 and 40 ^oC with an optimum at 30 ^oC.Its optimal water activity is 0.95 with a minimum of 0.75.

To read more about Aspergillus species click Aspergillus. The university of Manchester, UK has detailed information on Aspergillus at https://www.aspergillus.man.ac.uk/

 Penicillium chrysogenum

Penicillium chrysogenum is one of the most common indoor molds. It is extremely common on damp building materials, walls and wallpaper; floor, carpet mattress and upholstered-furniture dust. P. chrysogenum produces few detectable metabolites and often none when growing on building materials. Lack of observed effects on persons exposed to high quantities of spores and the production of few metabolites suggest this species may not be an important health hazard. However, some strains may cause allergenic reactions to susceptible individuals. P. chrysogenum can grow at a minimum temperature of -4 ^oC, an optimum of 28 ^oC, and a maximum of 38 ^oC. It has minimum water activity of 0.79 and an optimum at 0.98

Penicillium brevicompactum

Penicillium brevicompactum is common on damp walls and building materials e.g., gypsum board; floor, carpet, mattress and upholstered-furniture dust. P. brevicompactum produces mycophenolic acid. P. brevicompactum can grow at -2 and 30 ^oC with an optimum at 25 ^oC. Its water activity requirements are a minimum of 0.75 and an optimum at 0.96.

Chaetomium globosum

Chaetomium globosum is common on cellulose containing building materials that has been very wet such as gypsum board, cellulose board and wood. C. globosum produces high quantities of chaetoglobosins. The water activity requirement for C. globosum are a minimum of

 Trichoderma species

Trichderma species are frequently found on gypsum board and water saturated wood; floor, carpet and mattress dust; paint; domestic water supply, and HVAC system air. In one study, Trichoderma species were not found to produce detectable quantities of trichothecenes when growing on building materials. Less than 1% of the isolates produced trichodermol or esters of it. Compared with other indoor molds such as Cladosporium, Aspergillus and Penicillium, Trichoderma is not very common indoors.

References

Kuhn, D. M. and Ghannoum, M. A. (2003). Indoor Mold, Toxigenic Fungi, and Stachybotrys chartarum: Infectious Disease Perspective. Clinical Microbiology Reviews, 16(1):144–172.

Nielsen, K.F, (2002). Mould growth on building materials: Secondary metabolites, mycotoxins and biomarkers, Dissertation, The Mycology Group, Technical University of Denmark. 116p

When black mold is found growing in houses or commercial buildings, people panic.

Black mold is thought by the general public to be Stachybotrys chartarum or simply the ‘bad mold’. The truth is there are several molds that appear black and most of them are relatively harmless. Stachybotrys chartarum is a cellulose-degrading fungus (mold) commonly found in soil and on materials rich in cellulose such as hay, straw, cereal grains, plant debris, wood pulp, paper, and cotton.

Although it mainly survives as a saprophyte (i.e., by feeding on dead material), this type of mold has also been found to cause lesions on the roots of soybean plants. Presence of this mold in a building is an indication of an existing or previous water problem.

Stachybotrys: Was it the Cause of Death of Infants in Cleveland, Ohio, USA?

Stachybotrys chartarum is one of the most feared indoor molds since the 1993-1994 outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio, USA. Initial reports associated the outbreak with this mold, a fact that has remained controversial to date.

Some people now believe Stachybotrys chartarum was not solely the cause of these deaths. However, as early as the 1930s horses and other animals fed with straw and grains in Ukraine and other parts of eastern Europe were found to develop disease symptoms such as irritation of the mouth, throat, and nose; shock; dermal necrosis; a decrease in leukocytes; hemorrhage; nervous disorder; and death.

In 1938, Russian scientists conducted intensive studies and demonstrated that these symptoms were due to mycotoxins produced by Stachybotrys chartarum that had grown on the cellulose-rich straw. The disorders were subsequently named stachybotryotoxicosis. Stachybotryotoxicosis has also been reported in farm workers who handled contaminated straw.

Stachybotrys chartarum is known to produce a variety of mycotoxins. There is significant variation among isolates of Stachybotrys chartarum in the production of mycotoxins and other metabolites. Scientists are still studying Stachybotrys chartarum with the aim of understanding what the mold is comprised of.

Recent studies have indicated that the “species” previously believed to be S. chartarum was comprised of at least three strains. One of these strains was found not only to have a distinct secondary metabolite profile but also genetically differed from the other two strains and was thus renamed Stachybotrys chlorohalonata. The other two strains are still known as Stachybotrys chartarum. They differ in the amount and type of metabolites that they produce.

The variability of strains of S. chartarum in the production of mycotoxins has probably contributed to lack of consensus on the health effects of S. chartarum in indoor environments.

Contact MBL today if you have questions or require a black mold testing service.