Microbiological Insights into a Prevalent Human Metabolic Disease: The Gut Microbiota and Type 2 Diabetes

Abstract

Type 2 diabetes (T2D) is a multifactorial metabolic disease which has dramatically risen in prevalence in recent decades. Almost 400 million people are affected worldwide, and given the associated health costs and burden of secondary conditions, novel treatment methods are crucial. Growing evidence suggests that the intestinal microbiota influence many important host metabolic functions including digestion and immune modulation, and may be implicated in T2D. This thesis examines the diversity and community structure of gut bacteria of T2D patients and healthy controls. The ultimate goal is to improve the understanding of factors shaping bacterial communities and how these microorganisms potentially contribute to disease manifestation/progression. Samples were obtained from a previous study which had assessed T2D with respect to oxidative stress, copper ion homeostasis and heart disease in these patients. Male T2D subjects (n=20) and age-matched controls (n=20) underwent a factorial, randomised, double-blind, placebo-controlled, elemental balance study; with subjects on matched diets for 13 days. The basal period (days 1-6) preceded the administration of either a placebo or Cu-chelator and immediate entry into the treatment period (days 7-12). The availability of freeze-dried faecal samples from this well-replicated study provided the opportunity for microbiological analyses to be conducted on this sample set. DNA was extracted from faecal specimens and PCRamplified bacterial 16S rRNA genes were sequenced using the Illumina MiSeq platform. Given that the samples were originally collected in 2000 and 2001, their usability and comparability to newer collections of stool were examined; in terms of the core bacterial community, freeze-dried 14 year old faecal samples were indeed comparable to fresher samples collected in 2013. Healthy and T2D bacterial communities differed only slightly at baseline, though the onset of a new diet caused them to shift rapidly, independent of health status. Interestingly, treatment also displayed significant effects on shaping the gut microbiota, though this was dependent on the health status of the individual. Overall, inter-subject variability accounted for most of the variation observed. Gaining insights into the manipulable nature of the microbiota and its complex relationship with T2D supports the development of therapies (e.g. based on probiotics and/or prebiotics) targeting T2D and other metabolic diseases.