Diversity and quantity of bacteria in farm and non-farm environments and the relation to asthma and allergy

摘要

Background Prevalence of asthma and atopic diseases have increased in the last decades and it is clear that this trend is more pronounced in children living in cities compared with children who live in farm environments. There is still little known about the factors and mechanisms behind this protective quality. Aims The aim of this study was to identify bacterial exposures in the context of the farming environment that are associated with asthma or atopy. Methods Mattress dust samples were collected from children from farmers, exposed non-farmers and controls homes and analysed using denaturing gradient gel electrophoresis (DGGE) to obtain a spectrum of bacterial signals. Dichotomized DGGE bands occurrence data were analysed against asthma, atopy and other health outcomes and environmental factors using Tobit regression and Chi-square test. Bands with significant associations (p＜0.05) were identified; based on these findings, selected bacterial groups were subsequently targeted and quantified using quantitative polymerase chain reaction (qPCR). We used splined analysis, adjusted for age and gender, to explore associations between levels of microbes and health outcomes. Results All together 43 DOGE bands were found, six of them were significantly associated with asthma or atopy. Four bacterial groups were quantified via qPCR; Mycobacterium spp., Bifidobacterium spp., Clostridium spp. cluster Ⅰ and cluster Ⅺ. Enumeration in the different exposure strata resulted in highest levels of microbes in homes from farm children, except for Bifidobacterium spp.We observed inverse associations between levels of all of these bacterial groups and atopy; these associations were specifically visible in the non-farm children. Conclusions The study design and methodological approach followed here allowed to identify bacterial signals in mattress dust with indication to be protective for asthma and allergy. Quantitative levels of these bacterial groups confirmed inverse association to atopy in children.