Adipose tissue microbiota in humans: an open issue

BackgroundA specific "adipose tissue" microbiota has been recently identified in mice and hypothesized in humans. The purpose of this study was to verify the presence of microbiota of human whole adipose tissue and isolated adipocytes by combining culture-dependent and independent methods.MethodsStandard microbiological cultural techniques and 16S ribosomal RNA (16S rRNA) gene sequencing (Illumina technology) on DNA and RNA were employed to study a) whole abdominal subcutaneous (SAT) and visceral (VAT) adipose tissue from 14 obese and 5 normal-weight subjects, b) mature adipocytes isolated from SAT and VAT after collagenase digestion or mechanical separation. To optimize the 16S rRNA gene detection we used different DNA extraction methods (lysis with proteinase K, proteinase K+lysozyme and microbeads) and amplification procedures (semi quantitative standard PCR and real time quantitative PCR).ResultsMicrobiological cultures were negative in all analyzed samples. In enzymatically isolated adipocytes, 90% of the sequenced bacterial DNA belonged to Clostridium histolyticum, the bacterium from which the collagenase enzyme was isolated. Bacterial 16S rRNA gene was not detected from DNA and RNA of whole SAT and VAT, as well as of mechanically isolated mature adipocytes, even after blocking with a specific primer the non-specific amplification of human mitochondrial 12S rRNA.ConclusionOur results do not support the presence of a human adipose tissue microbiota. In addition, they emphasized the technical problems encountered when applying metagenomic studies to human tissues with very low or absent bacterial load