Mechanisms of allergy and clinical immunology
The occupant as a source of house dust bacteria

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Background

Markers for microbial groups are commonly measured in house dust samples to assess indoor exposure to microbes in studies on asthma and allergy. However, little is known about the sources of different microbes. A better understanding of the nature and origin of microbes present in the immediate environment of human beings is crucial if one wants to elucidate protective as well as adverse effects on human health.

Objective

To determine the extent to which the bacterial composition of mattress and floor dust reflects the presence of the human body in relation to other environmental sources.

Methods

House dust and skin surface swab samples of occupants in 4 homes were collected and analyzed for their bacterial content, using a culture-independent methodology. Bacterial sequences analyzed from the different house dusts and skin surface swabs represented random samples of bacteria present in a given sample. Highly similar sequences were grouped to assess biodiversity and to draw conclusions about the sources of bacteria.

Results

The bacterial flora in the house dust samples was found to be highly diverse and dominated by gram-positive bacteria. To a considerable extent, the presence of different bacterial groups was attributed to human sources. In the individuals' mattress dust samples, 69% to 88% of the bacterial sequences analyzed were associated with human origins. The respective percentages for the individual floor dusts ranged from 45% to 55%.

Conclusion

Our study indicates that human-derived bacteria account for a large part of the mainly gram-positive bacterial content in house dust.

Section snippets

Sample collection

Two female (individuals A and B) and 2 male volunteers (C and D) were recruited for the study. Dust samples from their homes as well as skin surface swab samples of the occupants themselves were taken by a field worker. Floor dust from the living room area was collected in nylon socks by vacuuming 1 m2 of a rug for 2 minutes (individuals A-C) or 4 m2 of smooth floor for 4 minutes (individual D); mattress dust was vacuumed for 2 minutes from the mattress surface. In all cases, freshly covered

Results

A total of 3294 bacterial 16S rRNA gene sequences derived from the individual samples were analyzed (Table I). The sampled species richness—expressed through the number of different SLOTUs detected in each sample—was found to be relatively low for the 4 skin surface swab samples compared with the mattress dust and floor dust samples. The observed bacterial richness as well as the Chao1 estimates of SLOTU richness assuming exhaustive sampling were always higher in the individual floor dust

Discussion

The findings of our study indicate that the human body is a major determinant of the bacterial content in house dust. We demonstrated that the majority of the bacterial sequences detected in mattress dust of 4 urban homes (69% to 88%) had a human origin. These sequences were directly linked to the individuals' skin surface flora or were clearly related to other human sources (mostly of oral, intestinal/fecal, or genital origins). Human-derived bacteria were less frequently found in floor dust

References (31)

  • C. Braun-Fahrländer et al.

    Environmental exposure to endotoxin and its relation to asthma in school-age children

    N Engl J Med

    (2002)
  • G. Bolte et al.

    Early endotoxin exposure and atopy development in infants: results of a birth cohort study

    Clin Exp Allergy

    (2003)
  • J.-H. Park et al.

    House dust endotoxin and wheeze in the first year of life

    Am J Respir Crit Care Med

    (2001)
  • A. Simpson et al.

    Endotoxin exposure, CD14, and allergic disease

    Am J Respir Crit Care Med

    (2006)
  • A. Saraf et al.

    Quantification of ergosterol and 3-hydroxy fatty acids in settled house dust by gas chromatography-mass spectrometry: comparison with fungal culture and determination of endotoxin by a Limulus amebocyte lysate assay

    Appl Environ Microbiol

    (1997)
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    Supported by the Academy of Finland with grant nos. 106103 and 111177.

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

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