Microbial content of house dust samples determined with qPCR

This study was designed to produce information about microbial concentrations using qPCR and their variation in different seasons and home environments with analyses of two types of house dust samples. Also the correlations between the two types of samples and the reproducibility of the parallel subsamples were studied. Two types of vacuumed house dust samples, rug dust and vacuum cleaner bag dust, were collected in 5 normal urban homes in four different seasons (N=20+20). From all dust samples, five parallel subsamples were subjected to qPCR analyses of 17 microbial species or assay groups of microbes. The highest fungal concentrations were found for the Penicillium/Aspergillus/Paecilomyces variotii group, and for the species Aspergillus penicillioides, Aureobasidium pullulans, Cladosporium cladosporioides and Cladosporium herbarum. These species/groups were present in almost all samples. The two types of dust samples gave similar results for most microbial species or groups analyzed, but in general, concentrations were slightly higher in rug dust than in dust from vacuum cleaner bag. Microbial concentrations varied significantly between different seasons and hence the similarity of samples within home was mainly low. The concentrations varied significantly also between different home environments. The reproducibility of the parallel subsamples was good or moderate for most of the analyzed species or assay groups. However, further studies are needed to fully understand the factors causing variation in these methods. Nevertheless, in order to show actual differences in fungal concentrations between urban homes with no known microbial sources, all dust samples to be compared should be taken during the same season.

Survival of amoebae on building materials

Moisture damage and concurrent microbial growth in buildings are associated with adverse health effects among the occupants. However, the causal agents for the symptoms are unclear although microbes are assumed to play a major role. Fungi and bacteria are not the only microbes inhabiting moist building materials; it was recently revealed that amoebae are also present. As amoebae have the potential to harbor many pathogens and to modulate the characteristics of growing microbes, a better appreciation of the growth and survival of amoebae in moisture damage conditions will add to the understanding of their effects on health outcomes. In this study, we investigated the ability of amoebae to survive on six building materials. Furthermore, both aged and unused materials were tested. Amoebae survived on gypsum board and mineral wool for the whole 2 months experiment even without additional sustenance. When sustenance (heat-killed bacteria) was available, aged pine wood and birch wood also allowed their survival. In contrast, amoebae were quickly killed on fresh pine wood and they did not survive on concrete or linoleum. In conclusion, our data show that amoebae can persist on several common building materials once these materials become wet.

PRACTICAL IMPLICATIONS

Amoebae are able to survive on many building materials should the materials become wet. Amoebae have the potential to increase growth, cytotoxicity, and pathogenicity of other microbes present in moisture damages, and they may carry potentially pathogenic bacteria as endosymbionts and thus introduce them into the indoor air. Therefore, amoebae may have a prominent role in the microbial exposures occurring in moisture-damaged buildings. The presence of amoebae could be usefully included in reporting the microbial damage of material samples.

Evaluation of quantitative PCR and culture methods for detection of house dust fungi and streptomycetes in relation to moisture damage of the house

AIMS

Microbial concentrations in vacuumed house dust samples (n = 71) were analysed by culture and quantitative polymerase chain reaction (qPCR) methods and their association with extent of moisture damage in the house was studied.

METHODS AND RESULTS

Microbial concentrations measured by qPCR correlated with concentrations obtained by culture method, but were orders of magnitude higher. qPCR also had better sensitivity. Concentrations of several microbes in house dust, determined with qPCR, were associated with the extent of moisture damage in the house. This association was strongest for Penicillium brevicompactum, one of the fungi detected in highest concentrations by qPCR. Furthermore, house dust concentrations of Wallemia sebi, Trichoderma viride, Cladosporium sphaerospermum, Eurotium amstelodami and the combined assay group for Penicillium spp., Aspergillus spp. and Paecilomyces variotii were significantly associated with the extent of the moisture damage.

CONCLUSION

These species or assay groups could probably be used as indicators of moisture damage in the house.

SIGNIFICANCE AND IMPACT OF THE STUDY

This finding indicates the benefits of the qPCR method, which is sensitive enough to reveal the differences in microbial concentrations of house dust between moisture-damaged and undamaged houses.

Predominance of Gram-positive bacteria in house dust in the low-allergy risk Russian Karelia

Simple living conditions and farming environment have been associated with reduced risk for allergic diseases such as atopy and asthma but the factors responsible for this effect remain unresolved. We examined the bacterial composition of house dusts obtained from Finnish and Russian Karelia, two adjacent areas with high and low occurrence of atopic diseases respectively. Two dust mixes, both composed of 10 randomly selected dust samples from 349 Finnish and 417 Russian Karelian households were studied for bacterial biomarkers (DNA, Limulus-active endotoxin, 3-OH fatty acids, muramic acid) and for 16S rRNA gene sequences. Overall, the DNA cloning revealed more taxons (94 different genera) of dustborne bacteria than seen in any previous study on residential environments. Majority (67%) of the bacterial DNA clones in house dust from the low-allergy Russian Kareliarepresented Gram-positive bacteria (Firmicutes and Actinobacteria), predominantly Staphylococcaceae and Corynebacteriaceae. Russian Karelian dust showed up to 20-fold higher contents of muramic acid (marker of Gram-positive bacteria) and a sevenfold higher number of clones of animal-associated species, whereas in Finnish Karelian dust Gram-negatives (mainly Proteobacteria) predominated. Clones of plant-associated bacterial species and of chloroplast, indicating plant biomass, were more numerous in Finnish than in Russian Karelian dust. In conclusion, this study revealed major disparities between Finnish and Russian house dusts. The higher bacterial content and the predominance of Gram-positive bacteria in Russian dust may have implications for occurrence of atopy.

Monitoring success of remediation: seven case studies of moisture and mold damaged buildings

Based on seven case studies of buildings that underwent different degrees of moisture and mold damage remediation, we aimed to develop methodology for assessment of the success of the remediation process. Methods used in gauging the success included technical monitoring of performance of building structures and heating, ventilation and air conditioning (HVAC) systems, microbial monitoring of indoor air quality (IAQ), and health effects studies of building occupants. The assessment was based on measurable change in the situations before and after remediation. Based on technical monitoring, remediation was successful in three cases, with partial improvement noted in three cases, whereas no remediation was conducted in one case. Based on microbial monitoring, improvement was detected in one, partial improvement in two and no improvement in two cases, whereas no follow-up was conducted in two cases. Health effect studies (mainly self-reported health status) showed improvement in one case, partial improvement in two cases, and no improvement in two cases, whereas no follow-up was conducted in one case, and in one case, follow-up failed due to low response rate. The results illustrate that it is possible to monitor the effects of remediation using various metrics. However, in some cases, no improvement could be observed in IAQ or occupant health, even if the remediation was considered technically successful, i.e. the remediation was fully completed as recommended. This could be due to many reasons, including: 1) all damage may not have been addressed adequately; 2) IAQ or health may not have been perceived improved regardless of remediation; and/or 3) the methods used may not have been sensitive/specific enough to detect such improvement within the 6-12 months follow-up periods after completion of the remediation. There is a need to further develop tools for monitoring and assessment of the success of moisture damage remediation in buildings.

Indoor air particles and bioaerosols before and after renovation of moisture-damaged buildings: the effect on biological activity and microbial flora

Many building-related health problems coincide with moisture damage and mold growth within a building. Their elimination is assumed to improve indoor air quality. The aim of this study was to follow the success of remediation in two individual buildings by analyzing the microbial flora and immunotoxicological activity of filter samples. We compare results from samples collected from indoor air in the moisture-damaged buildings before and after renovation and results from matched reference buildings and outdoor air. The microbial characteristics of the samples were studied by analyzing ergosterol content and determining the composition of fungal flora with quantitative polymerase chain reaction (QPCR). In addition, the concentrations of particles were monitored with optical particle counter (OPC). The immunotoxicological activity of collected particle samples was tested by exposing mouse macrophages (RAW264.7) for 24 h to particle suspension extracted from the filters, and measuring the viability of the exposed cells (MTT-test) and production of inflammatory mediators (nitric oxide, IL-6 and TNF*) in cell culture medium by enzyme-linked immunoassay (ELISA). The results show that for Location 1 the renovation decreased the immunotoxicological activity of the particles collected from damaged building, whereas no difference was detected in the corresponding samples collected from the reference building. Interestingly, only slight differences were seen in the concentration of fungi. In the Location 2, a decrease was seen in the concentration of fungi after the renovation, whereas no effect on the immunotoxicological responses was detected. In this case, the immunotoxicological responses to the indoor air samples were almost identical to those caused by the samples from outdoor air. This indicates that the effects of remediation on the indoor air quality may not necessarily be readily measurable either with microbial or toxicological parameters. This may be associated with different spectrum of harmful agents in different mold and moisture-damaged buildings.

Diversity and seasonal dynamics of bacterial community in indoor environment

Background

We spend most of our lives in indoor environments and are exposed to microbes present in these environments. Hence, knowledge about this exposure is important for understanding how it impacts on human health. However, the bacterial flora in indoor environments has been only fragmentarily explored and mostly using culture methods. The application of molecular methods previously utilised in other environments has resulted in a substantial increase in our awareness of microbial diversity.

Results

The composition and dynamics of indoor dust bacterial flora were investigated in two buildings over a period of one year. Four samples were taken in each building, corresponding to the four seasons, and 16S rDNA libraries were constructed. A total of 893 clones were analysed and 283 distinct operational taxonomic units (OTUs) detected among them using 97% sequence similarity as the criterion. All libraries were dominated by Gram-positive sequences, with the most abundant phylum being Firmicutes. Four OTUs having high similarity to Corynebacterium-, Propionibacterium-, Streptococcus- and Staphylococcus- sequences were present in all samples. The most abundant of the Gram-negative OTUs were members of the family Sphingomonadaceae, followed by Oxalobacteraceae, Comamonadaceae, Neisseriaceae and Rhizobiaceae.

The relative abundance of alpha- and betaproteobacteria increased slightly towards summer at the expense of firmicutes. The proportion of firmicutes and gammaproteobacteria of the total diversity was highest in winter and that of actinobacteria, alpha- and betaproteobacteria in spring or summer, whereas the diversity of bacteroidetes peaked in fall. A statistical comparison of the libraries revealed that the bacterial flora of the two buildings differed during all seasons except spring, but differences between seasons within one building were not that clear, indicating that differences between the buildings were greater than the differences between seasons.

Conclusion

This work demonstrated that the bacterial flora of indoor dust is complex and dominated by Gram-positive species. The dominant phylotypes most probably originated from users of the building. Seasonal variation was observed as proportional changes of the phyla and at the species level. The microflora of the two buildings investigated differed statistically and differences between the buildings were more pronounced than differences between seasons.

Comparison of mold concentrations quantified by MSQPCR in indoor and outdoor air sampled simultaneously

Mold specific quantitative PCR (MSQPCR) was used to measure the concentrations of the 36 mold species in indoor and outdoor air samples that were taken simultaneously for 48 h in and around 17 homes in Cincinnati, Ohio. The total spore concentrations of 353 per m(3) of indoor air and 827 per m(3) of outdoor air samples were significantly different (p<or=0.05). However, only the concentrations of Aspergillus penicillioides, Cladosporium cladosporioides types 1 and 2 and Cladosporium herbarum were correlated in indoor and outdoor air samples (p-value<or=0.05 and sufficient data for estimate and absolute value rho estimate >or=0.5). These results suggest that interpretation of the meaning of short-term (<48 h) mold measurements in indoor and outdoor air samples must be made with caution.

Effects of co-culture of amoebae with indoor microbes on their cytotoxic and proinflammatory potential

Free-living amoebae are ubiquitous environmental protozoa found in both natural and man-made environments, including moisture-damaged buildings. Furthermore, the interaction between amoebae and bacteria has been shown to enhance the virulence and pathogenicity of some bacteria. While the inhabitants of moisture damaged buildings are known to be at risk of suffering adverse health effects, the exact causative agents and mechanisms are still obscure. To examine the possible role of amoebae in the health effects associated with moisture damages, the effects of amoebae on the cytotoxicity and proinflammatory potential of nonpathogenic microbes common in moisture-damaged buildings were investigated. First, two bacterial and three fungal strains were cultured both individually and in coculture with Acanthamoeba polyphaga. Then, mouse RAW264.7 macrophages were exposed to the cocultures as well as the individually grown bacteria, fungi, and amoebae. Finally, cell viability and production of proinflammatory mediators, i.e., nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha), and interleukin 6 (IL-6), were measured in macrophages after the exposure. The results revealed that cocultivation with amoebae increased the cytotoxicity of the bacterium Streptomyces californicus and the fungus Penicillium spinulosum. Moreover, the macrophages produced up to 10 times higher concentrations of NO after the exposure to these cocultures than after the exposure to individually grown microbes. Finally, the production of the cytokines was up to two orders of magnitude higher (IL-6) and up to four times higher (TNF-alpha) after exposure to the cocultures when compared to individually grown microbes. We conclude that amoebae are able to potentiate the cytotoxicity and proinflammatory properties of certain microbes associated with moisture damages.

Elements that contribute to healthy building design

BACKGROUND

The elements that contribute to a healthy building are multifactorial and can be discussed from different perspectives.

OBJECTIVES

WE PRESENT THREE VIEWPOINTS OF DESIGNING A HEALTHY BUILDING: the importance of sustainable development, the role of occupants for ensuring indoor air quality, and ongoing developments related to indoor finishes with low chemical emissions and good fungal resistance.

DISCUSSION

Sustainable design rediscovers the social, environmental, and technical values of pedestrian and mixed-use communities, using existing infrastructures including "main streets" and small-town planning principles and recapturing indoor-outdoor relationships. This type of design introduces nonpolluting materials and assemblies with lower energy requirements and higher durability and recyclability. Building occupants play a major role in maintaining healthy indoor environments, especially in residences. Contributors to indoor air quality include cleaning habits and other behaviors; consumer products, furnishings, and appliances purchases, as well as where and how the occupants use them. Certification of consumer products and building materials as low-emitting products is a primary control measure for achieving good indoor air quality. Key products in this respect are office furniture, flooring, paints and coatings, adhesives and sealants, wall coverings, wood products, textiles, insulation, and cleaning products. Finishing materials play a major role in the quality of indoor air as related to moisture retention and mold growth.

CONCLUSIONS

Sustainable design emphasizes the needs of infrastructure, lower energy consumption, durability, and recyclability. To ensure good indoor air quality, the product development for household use should aim to reduce material susceptibility to contaminants such as mold and should adopt consumer-oriented product labeling.

Personal and microenvironmental concentrations of particles and microbial aerosol in relation to health symptoms among teachers

A total of 81 randomly selected elementary school teachers participated in two sampling campaigns conducted 2 weeks apart during the winter. A 24-h sample collection was performed using personal and microenvironmental sampling from homes, and an 8-h sample collection was performed from workplaces of the studied subjects. Filters were analyzed for particle mass, absorption coefficient of the filter, and for both total and viable microorganisms. Comprehensive questionnaire responses were collected from the teachers concerning weekly occurred symptoms during the previous 12-month period, and they filled in symptom diaries immediately after each sampling campaign concerning symptoms during the previous 24-h and 7-day periods. The effect of different recall periods on agreement between questionnaire responses was assessed. Factor analysis was used in order to identify factors explaining the pattern of correlations within the personal, home, and work measurements. Moreover, associations between personal, home, and work measurements of pollutants and symptoms were analyzed using general estimation equations. The recall period of 7 days seemed to provide the most reliable data for the health effect assessment. Information from the factor analysis may allow reduction of variables related to the exposure assessment, and better interpretation of results. Both personal exposure and concentrations of pollutants at home were more frequently associated with health symptoms than concentrations at work. In multipollutant analyses, absorbance coefficient was positively associated with eye symptoms, and total bacteria with both cough and blocked nose.

Effects of moisture damage and renovation on microbial conditions and pupils' health in two schools--a longitudinal analysis of five years

Airborne microbes and pupils' symptoms were monitored in a moisture-damaged (index) school and a reference school for five consecutive years. These surveys were carried out in two separate years before the renovation of the index school, during the renovation, and one and two years after the renovation. Microbial concentrations were higher in the index school than those in the reference school before and during renovation, but afterwards, the levels decreased to the level of the reference school. The effect of remediation was seen as an altered mycobiota in the index school. Year-to-year variation of microbial concentrations, probably due to climatic factors, caused a peak in both schools but their difference remained. Several symptoms were more prevalent in the moisture-damaged school than in the reference school, but the differences disappeared during the renovations. These results emphasize the importance of using a reference building in assessing the microbial conditions of a moisture damaged building. Furthermore, microbial concentrations reflected well the technical condition of the construction, but the reported symptoms of the occupants did not strictly follow the timely fluctuation in microbial conditions.

Skin test reactivity to molds in pre-school children with newly diagnosed asthma

BACKGROUND

The aim of the present study was to evaluate the prevalence of sensitization to molds and to house dust mites (HDM) in pre-school children with newly-diagnosed asthma.

METHODS

From 1996 to 2000, 122 children 1 to 6 years of age with fresh asthma treated in the Kuopio University Hospital, Kuopio, Finland, were recruited in the study; 94% attended. Skin prick tests were performed to common inhalant allergens and to 10 molds. The homes were surveyed for moisture damage.

RESULTS

A majority of the houses had signs of dampness and moisture. One-third of the children reacted to inhalant allergens. There were 11 positive reactions to molds in five children who all reacted to at least one animal dander or seasonal pollen. Aspergillus fumigatus, Botrytis cinerea, and Cladosporium herbarum were the most common mold allergens. There were only two children with positive reactions to HDM, and none of them reacted to molds. No associations were found between the presence or degree of moisture problems at home and mold or HDM allergy.

CONCLUSION

Sensitization to molds seems to play only a minor role in pre-school children with newly-diagnosed asthma in a northern climate where the incidences of mold and HDM allergies are rather low.

A preliminary study on the association between ventilation rates in classrooms and student performance

Poor conditions leading to substandard indoor air quality (IAQ) in classrooms have been frequently cited in the literature over the past two decades. However, there is limited data linking poor IAQ in the classrooms to student performance. Whereas, it is assumed that poor IAQ results in reduced attendance and learning potential, and subsequent poor student performance, validating this hypothesis presents a challenge in today's school environment. This study explores the association between student performance on standardized aptitude tests that are administered to students on a yearly basis, to classroom carbon dioxide (CO2) concentrations, which provide a surrogate of ventilation being provided to each room. Data on classroom CO2 concentrations (over a 4-5 h time span within a typical school day) were recorded in fifth grade classrooms in 54 elementary schools within a school district in the USA. Results from this preliminary study yield a significant (P < 0.10) association between classroom-level ventilation rate and test results in math. They also indicate that non-linear effects may need to be considered for better representation of the association. A larger sample size is required in order to draw more definitive conclusions. Practical Implications Future studies could focus on (1) gathering more evidence on the possible association between classroom ventilation rates and students' academic performance; (2) the linear/non-linear nature of the association; and (3) whether it is possible to detect 'no observed adverse effect level' for adequate ventilation with respect to academic performance in schools. All of this information could be used to improve guidance and take regulatory actions to ensure adequate ventilation in schools. The high prevalence of low ventilation rates, combined with the growing evidence of the positive impact that sufficient ventilation has on human performance, suggests an opportunity for improving design and management of school facilities.

Moisture damage and childhood asthma: a population-based incident case-control study

Most previous studies on the association between moisture damage and asthma have been cross-sectional and relied on self-reported exposure and health. The present authors studied the association by carrying out careful home inspections among new, clinically determined cases of asthma and controls. New cases of asthma aged 12-84 months (n = 121) were recruited prospectively and matched for year of birth, sex and living area with two randomly selected population controls (n = 241). Trained engineers visited all homes. Both cases and controls had lived >or=75% of their lifetime or the past 2 yrs in their current home. Risk of asthma increased with severity of moisture damage and presence of visible mould in the main living quarters but not in other areas of the house. Cases more often had damage in their bedroom. Associations were comparable for atopic and nonatopic asthma and for children aged >30 months or <or=30 months. The present results, using standardised assessment of exposure and asthma, suggest that moisture damage and mould growth in the main living quarters are associated with the development of asthma in early childhood.

Mycobacteria and fungi in moisture-damaged building materials

In contrast to the growth of fungi, the growth of mycobacteria in moisture-damaged building materials has rarely been studied. Environmental mycobacteria were isolated from 23% of samples of moisture-damaged materials (n = 88). The occurrence of mycobacteria increased with increasing concentrations of fungi. Mycobacteria may contribute to indoor exposure and associated adverse health effects.

Characterizing microbial exposure with ergosterol, 3-hydroxy fatty acids, and viable microbes in house dust: determinants and association with childhood asthma

The authors assessed determinants of ergosterol, 3-OH fatty acids (FAs), and viable microbes in vacuum cleaner dust, and investigated the association between these microbial markers and childhood asthma. The authors studied the homes of 36 children who were new cases of childhood asthma and the homes of 36 controls. Home characteristics explained 34% to 44% of the variation in levels of different microbial groups. Determinants of 3-OH FAs were a lower level of cleanliness, having a fireplace, having livestock, and moisture damage; determinants of viable bacteria were the level of home repair needed and the material used in the building frame of the home. Ergosterol was associated with the presence of livestock and the practice of cleaning rugs outside; viable fungi was associated with the material used in the building frame, visible mold, and the practice of cleaning rugs outside. Exposure to mesophilic actinomycetes was nonsignificantly associated with risk of asthma. The authors concluded that the variation of microbial levels in dust could be explained relatively well by home characteristics, and suggested that exposure to mesophilic actinomycetes may increase the risk of new asthma.

Simkania negevensis and newly diagnosed asthma: a case-control study in 1- to 6-year-old children

BACKGROUND

Simkania negevensis is an intracellular bacterium, sharing many characteristics with Chlamydophila and Chlamydia species. S. negevensis infection has been associated with bronchiolitis in infants and with pneumonia and exacerbations of COPD in adults.

OBJECTIVE

The aim of the present study was to evaluate, in a case-control setting, whether S. negevensis serology had any association with the onset of asthma in children.

METHODS

S. negevensis-specific IgM, IgA and IgG antibodies were measured by microimmunofluorescence in 104 children below school-age with newly diagnosed asthma, and in 122 control children.

RESULTS

S. negevensis-specific IgM was detected in two (2%) cases and in nine (8%) of the controls. IgG was detected in 12 (12%) cases and 12 (10%) of the controls. IgA antibodies were absent in all children. The age distribution of the 35 children with S. negevensis-specific antibodies was even, the positivity rate being 11% in the 12- to 23-month-old group and 20-23% in the children aged between 2 and 5 years.

CONCLUSION

Although S. negevensis appears to cause infections in the Finnish preschool-aged population, there was no association with asthma.

Children's homes--determinants of moisture damage and asthma in Finnish residences

Certain housing characteristics increase the risk for moisture damage, which has been associated with increased risk for asthma in children. Modeling moisture damage as a function of these characteristics could therefore provide a simple tool to estimate building-related risk for asthma. This study aimed to find out specific associations between asthma case-control status of children and moisture damage and housing characteristics. The data consisted of information on 121 asthmatic children and predominately two age-, gender- and place of residence-matched control children for every case, and information on moisture damage and housing characteristics in the homes of the children. In a previous study, we found a statistically significant association between moisture damage observations in main living areas and asthma in children. Using logistic regression, five models were formulated to predict moisture damage status of the homes and moisture damage status of living areas. The models were able to classify the damage status correctly in 65.0-87.7% of the homes (kappa values 0.10-0.47) as functions of housing characteristics. None of the models qualified as a significant determinant of the case-control status of the children.

PRACTICAL IMPLICATIONS

It can be hypothesized that building-related risk for asthma could be roughly estimated using models predicting moisture damage status of buildings as a function of easily obtainable housing characteristics. The results of this study indicated that, with a moderate certainty, it is possible to model moisture damage status of buildings using housing characteristics. However, the models developed did not associate with asthma in children. In conclusion, it was not possible to estimate the risk for asthma by studying housing characteristics only, but detailed information on moisture damage (e.g. location of damage) was crucial for such estimation.

Effects of amoebae on the growth of microbes isolated from moisture-damaged buildings

Dampness, moisture, and mold in buildings are associated with adverse health outcomes. In addition to fungi and bacteria, amoebae have been found in moisture-damaged building materials. Amoebae and a growing list of bacteria have been shown to have mutual effects on each other's growth, but the interactions between amoebae and microbes common in moisture-damaged buildings have not been reported. We co-cultivated the amoeba Acanthamoeba polyphaga with bacteria and fungi isolated from moisture-damaged buildings in laboratory conditions for up to 28 days. The microbes selected were the bacteria Streptomyces californicus, Bacillus cereus, and Pseudomonas fluorescens, and the fungi Stachybotrys chartarum, Aspergillus versicolor, and Penicillium spinulosum. Fungi and bacteria generally benefited from the presence of the amoebae, whereas the growth of amoebae was hindered by Streptomyces californicus, Stachybotrys chartarum, and Bacillus cereus. Pseudomonas fluorescens slightly enhanced amoebae viability. Amoebae were indifferent to the presence of Aspergillus versicolor and Penicillium spinulosum. Thus, our results show that amoebae can alter the survival and growth of some microbes in moisture-damaged buildings.Key words: moisture-damaged buildings, free-living amoebae, bacteria, fungi, co-culture.

Dust sampling methods for endotoxin - an essential, but underestimated issue

Exposure to farming environment in early life has been associated with lower risk for allergic diseases possibly caused by increased exposure to endotoxin. The aims of this study were to compare the reproducibility of different sampling methods for endotoxin, and to determine whether environmental characteristics have different effect on endotoxin levels of different sample types. The reproducibility of sampling methods (bed dust, floor dust, vacuum cleaner dust bag dust, settled dust and air samples) was studied with repeated sampling (five visits during 1 year) in five farming and five urban homes. To examine determinants of endotoxin for different types of dust sample, sampling was conducted once in 12 farming and 17 urban homes. Endotoxin was analyzed using Limulus Amebocyte Lysate assay. Bed dust samples had the best reproducibility (intraclass correlation, ICC=66%), but the difference between farming and non-farming homes was not clear with this sample type. The reproducibility of floor (ICC=52%) and settled dust (ICC=51%) was moderate. With these sample types the difference between farming and non-farming homes was clear. Settled dust had some seasonal variation. Based on this study, the best compromise for sampling for endotoxin appears to be floor dust sample followed by bed and settled dust samples. Practical Implications Endotoxins have been widely measured, even though the validity of different sample types to reflect the endotoxin exposure level of an indoor environment is poorly known. This study shows that bed dust samples have the best reproducibility, but they do not reflect the differences in exposure due to environmental factors such as farming. Floor dust samples with moderate reproducibility may be the best choice for sampling of endotoxin in large field studies.