Year: 2009
Type: article
Abstract: Moisture damage in buildings and consequent microbial growth are associated with adverse health effects suffered by the occupants.Although the association is well documented epidemiologically, the exact causative agents for the health effects are not usually known.Even though the microbial network growing on moisturedamaged building materials is a complex ecosystem consisting of many types of organisms including bacteria, yeasts, fungi, protozoa, and mites, exposure has mainly been described in terms of fungal and bacterial diversity and quantity.It is important not to overlook the other possible organisms growing on these materials to better understand the link between the exposure and the symptoms.In this thesis, the occurrence and role of amoebae in moisture damage is elucidated.First, the prevalence of amoebae in moisture-damaged buildings was estimated by screening 124 building material samples.Then amoebal survival on moist building materials was studied by inoculating samples of building materials with Acanthamoeba polyphaga and incubating those in 100 % relative humidity for 0-56 days.Thirdly, the effects of amoebae on other microbes commonly found in moisture-damaged buildings were assessed by co-cultivating three bacterial (Streptomyces californicus, Bacillus cereus, and Pseudomonas fluorescens) and three fungal strains (Stachybotrys chartarum, Aspergillus versicolor, and Penicillium spinulosum) together with A. polyphaga and also individually for up to 28 days.Their growth was measured at different times during the incubation.Finally, the effects of this co-culture on the cytotoxic and proinflammatory potential of the microbes were studied by exposing RAW264.7 mouse macrophages to graded doses of co-cultured and individually grown fungi, bacteria and amoebae.Amoebae were found in 22 % of the samples and they often were detected at the same locations as "indicator microbes" of moisture damage, e.g. with the bacterium Streptomyces, and with the fungi Acremonium, Trichoderma, Chaetomium, and Aspergillus versicolor.In the inoculation tests, A. polyphaga amoebae survived throughout the two-month experiment on samples of mineral insulation, old pine plank, birch plank and gypsum board, often even without nutrient supplementation.All materials with the exception of fresh pine plank, supported amoebal survival at least temporarily.Furthermore, co-cultivation with amoebae significantly increased the growth of all bacteria studied, whereas with fungi, only a modest increase in the growth was observed.Co-culturing also affected the toxicity and proinflammatory potential of two of the studied strains: the ability of P. spinulosum and S. californicus to induce the production of inflammatory mediators -nitric oxide, TNFα and IL-6 -in RAW264.7 macrophages was increased manifold.In addition, their cytotoxicity was somewhat increased after incubation with amoebae.The results of this study show that amoebae are members of the microbial network present in moisture-damaged building materials.The interaction with amoebae could lead to alterations in the properties of the other microbes present in the waterdamaged structures.Amoebae may increase the growth of other microbes present, and render the microbes more cytotoxic.Thus, amoebae may indirectly modify the health effects associated with moisture-damaged buildings.However, more evidence from both empirical and epidemiological studies is needed before the role of amoebae as exposing agents in moisture-damaged buildings is fully understood.
Author: Terhi Yli‐Pirilä
Language: English
Subfield: Health, Toxicology and Mutagenesis
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W247628581