the bacteria supports a diverse species population in the colon. The complex microbiota in the large bowel is structurally and metabolically diverse with over 1,000 species of bacteria reported to be present. Data on gut contents of sudden death victims was used to explain the process of metabolism in the large bowel which occurs by either the glycolytic pathway or the pentose phosphate pathway. There has been a lot of interest in energy generation from short chain fatty acids in the gut due to research looking at obesity and microbiotas; George explained that short chain fatty acids alone could not explain why an individual may be obese, as data indicate that 400mmol of short chain fatty acids are produced each day which equates to around 5% of the host’s daily requirements. Although getting 5% of our daily requirements from carbohydrate fermentation in the gut is not a great deal for someone living on a Westernstyle diet, however, it could mean life or death for someone that is starving in a Third World country, as the majority (95%) of fatty acids are absorbed by the large bowel and are metabolized by the host. Molar ratios of short chain fatty acids were shown to vary across sites in the body, which is due to the fact that different fatty acids produced by different bacteria in the large bowel are cleared in different body organs. Branched chain fatty acids were described as being excellent markers of fatty acid production from proteins and in vitro modelling studies indicate that around 30% of all fatty acids derived from proteins are branched chain fatty acids. However, this varies from 17% of all short chain fatty acids in the proximal colon arising from protein, up to 38% in the distal colon which indicates a change from carbohydrate to protein digestion by bacteria between the proximal and distal colon. Furthermore, the percentage of branched chain fatty acids was calculated at different pH levels.
www.sfam.org.uk
Due to carbohydrate fermentation, the pH of the proximal bowel is more acidic than the distal colon, which explains why fewer protein breakdown products accumulate in the proximal gut as the proximal bowel proves to be very metabolically active. Interestingly, between 0.5–4.0 litres of hydrogen are produced in the bowel each day, most of which is lost through breath, however much is cross fed by other species. A study in which volunteers consumed sulfate with meals determined that methane production dropped during sulfate consumption, which indicates the effect that small changes in the diet can have big metabolic effects on some bacterial populations in the gut. It was also fascinating to hear George discuss the difficulties experienced in obtaining some of the samples that some of the data had originated from and we all shared in his humour during the lecture, particularly in his cartoon summary of fermentation in the gut. Monday concluded with a drinks reception and the ever-popular quiz night.
Ellen Evans
Tuesday 1 July SESSION 1: Risk Research The first conference session, Risk research, started on Tuesday morning. The first speaker of the day Arie Havelaar, National Institute for Public Health and the Environment, and University of Utrecht, gave a fascinating talk on ‘The influence of acquired immunity and dose-dependent probability of illness on the risk assessment of Campylobacter jejuni.’ Arie’s talk presented findings from a recent study on microbial risk assessment which, had considered two steps, exposure to infection and infection to illness, as well as acquired immunity in the process leading to actual illness. Arie’s team had found that at low doses the inclusion of the infection to illness step had the greatest impact on risk estimates whereas at higher doses the inclusion of an inflation factor representing acquired immunity had the greatest impact. The team hope that this study can form the basis for further development of microbial dose-response modelling.
microbiologist
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December 2014
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