Abstract
For psoriasis, an idiopathic inflammatory disorder of the skin, the microbial biota has not been defined using cultivation-independent methods. We used broad-range 16S rDNA PCR for archaea and bacteria to examine the microbiota of normal and psoriatic skin. From 6 patients, 19 cutaneous samples (13 from diseased skin and 6 from normal skin) were obtained. Extracted DNA was subjected to the broad range PCR, and 1,925 cloned products were compared with 2,038 products previously reported from healthy persons. Using 98% sequence identity as a species boundary, 1,841 (95.6%) clones were similar to known bacterial 16S rDNA, representing 6 phyla, 86 genera, or 189 species-level operational taxonomic unit (SLOTU); 84 (4.4%) clones with <98% identity probably represented novel species. The most abundant and diverse phylum populating the psoriatic lesions was Firmicutes (46.2%), significantly (P<0.001) overrepresented, compared to the samples from uninvolved skin of the patients (39.0%) and healthy persons (24.4%). In contrast, Actinobacteria, the most prevalent and diverse phylum in normal skin samples from both healthy persons (47.6%) and the patients (47.8%), was significantly (P<0.01) underrepresented in the psoriatic lesion samples (37.3%). Representation of Propionibacterium species were lower in the psoriatic lesions (2.9±5.5%) than from normal persons (21.1±18.2%; P<0.001), whereas normal skin from the psoriatic patients showed intermediate levels (12.3±21.6%). We conclude that psoriasis is associated with substantial alteration in the composition and representation of the cutaneous bacterial biota.
Highlights
The microbiota of humans is vast in extent and in its diversity, but little characterized [1,2]
Species richness and diversity Estimations of species coverage, richness, evenness, and diversity were calculated for the combined data set of 3,963 clones, as well as for subsets of samples defined based on sources of specimens [healthy subjects or subjects with psoriasis] and pathology [psoriatic lesion or uninvolved skin] (Table 1)
Good’s coverage, which accounts for both diversity and abundance, at 97% for the overall sequence set, indicated that the small subunit rRNA gene (16S rDNA) sequences identified in these samples represent the majority of bacterial sequences present in the human skin samples under study
Summary
The microbiota of humans is vast in extent and in its diversity, but little characterized [1,2]. The microbiota was defined by the isolation of organisms in culture, but substantial proportions of bacterial and fugal species are fastidious, resisting cultivation [2,4]. This is true for human skin, for which recent analyses using molecular methods have revealed a microbiota of considerable diversity, much greater than anticipated from culture-based studies [10,11,12]. A chronic inflammatory condition of the skin, present in about 2% of the world’s population [13], affects cardiovascular disease risk [14,15]. The causes of psoriasis are poorly understood, the disease appears to result from a combination of genetic and environmental factors; putative loci for genetic susceptibility to psoriasis have been reported on the basis of genome-wide linkage studies [13]
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