title: Gut microbiota as a risk factor and marker for norovirus infection
Creators: name: Puławska-Czub, Anna
Publisher: name: University of Liverpool Repository
Year: 2020

description: INTRODUCTION The Human Microbiome Project has disclosed that the dense and diverse microenvironment of the human gastrointestinal tract harbours microbial communities that vary significantly across healthy individuals. The composition of the microbiota was found to be strongly dependent upon complex interactions between the host’s age, genetics and environmental factors, including diet and lifestyle. These disparities could explain why some individuals are more susceptible to gastrointestinal infections or gut inflammatory diseases, and why the range of symptoms and their severity can vary substantially from person to person. The growing awareness of the major role that the gut microbiota plays in an individual’s health and disease, has contributed to the considerable increase in the number microenvironmental studies being undertaken. At the same time, the rapid technological development of cost-effective, high-throughput sequencing technologies has resulted in a greatly expanded choice of analytical procedures. The wide range of methodological variables and lack of standardized procedures, can introduce various biases at any phase of a multistep sequencing process. OPTIMIZATION OF METAGENOMIC STUDY APPROACH Here, a systematic study was performed in order to comprehend how changes introduced at each step of a faecal microbiota sequencing procedure could affect the final picture of the inherent microbial structure. Sample handling techniques were found to either reduce or promote the expansion of specific microorganisms present in a specimen. The tested extraction methods differed in their efficiency of DNA recovery from either gram-positive or gram-negative bacteria, and the choice of sequencing technique influenced the final observations, which could thus lead to incorrect microbial profiling of the explored environment. However, the significance of the effect that these methodological variables had on the final microbial profile was strongly dependent on the initial composition of the microbiota and the disease/recovery status of the donor. Therefore, characteristics of the recruited study group, particularly the age range, frailty status and specific medicinal/probiotic intake, should be taken into consideration when choosing the appropriate methodology. It is important to thoroughly understand the limitations of each stage and avoid implementing biases by selecting techniques that have already been reported as inappropriate for a specific experimental design or study group. GUT MICROBIOTA AS A RISK FACTOR AND MARKER FOR NOROVIRUS INFECTION Once a faecal microbiota profiling methodology had been selected based on the results of the optimization studies, it was used to carry out two major investigations involving larger study populations. The main aim of both studies was to identify host-associated risk factors connected with norovirus (NoV) infection, especially among elderly residents of long-term care facilities, and to recognize biomarkers within virus-affected gut microbiota. It was confirmed that non-secretors (sese secretor genotype, LeA Lewis phenotype), were significantly less susceptible to NoV infection; however, the risk of acquiring an infection increased with progressing age and frailty, indicating that the genetic background provides only partial protection. Furthermore, the increased susceptibility to NoV was found to be associated with high numbers of Akkermansia municiphila and the Odoribacteriaceae family, and feasibly with a low abundance of Faecalibacterium, in an individual’s faecal material. Throughout the infection, only 30% of NoV-diagnosed individuals displayed a severe microbiota dysbiosis, manifested by the overgrowth of Proteobacteria (represented by Escherichia spp.) and loss of Lachnospiraceae, Rikenellaceae and Ruminococcaceae (especially Faecalibacterium) families in the intestinal environment. The severity of microbiota dysbiosis following exposure to the pathogen, could worsen the final outcome of the disease and conceivably elevate the risk of developing long-lasting complications, such as inflammatory bowel disease or irritable bowel syndrome. Interestingly, similarly disrupted microbiota profiles were observed across healthy elderly people living in long-term care facilities. Studying this specific group confirmed that the microbial composition of the lower gastrointestinal tract is significantly dependent upon the host’s age and frailty status, and also the genetic background (gender, secretor and Lewis status), living environment and associated comorbidities. A greater understanding of these multifactorial associations would help determine who is at higher risk of developing more severe outcomes of infectious gastroenteritis and eventually pave the way for its prevention and personalised treatments. Furthermore, the characterization of alterations in the faecal microbiota occurring throughout the infection could lead to better monitoring of the disease progress and the response to treatment, which would help protect patients from long-term health complications.