Human colonic microbiota associated with diet, obesity and weight loss.

BACKGROUND: It has been proposed that the development of obesity in humans is influenced by the relative proportions of the two major phyla of bacteria (Bacteroidetes and Firmicutes) present in the large intestine. OBJECTIVE: To examine the relationships between body mass index, weight loss and the major bacterial groups detected in fecal samples. DESIGN: Major groups of fecal bacteria were monitored using fluorescent in situ hybridization (FISH) in obese and non-obese subjects under conditions of weight maintenance, and in obese male volunteers undergoing weight loss on two different reduced carbohydrate weight-loss diets given successively for 4 weeks each. RESULTS: We detected no difference between obese and non-obese individuals in the proportion of Bacteroidetes measured in fecal samples, and no significant change in the percentage of Bacteroidetes in feces from obese subjects on weight loss diets. Significant diet-dependent reductions in a group of butyrate-producing Firmicutes were, however, detected in fecal samples from obese subjects on weight loss diets. CONCLUSIONS: Diets designed to achieve weight loss in obese subjects can significantly alter the species composition of the gut microbiota, but we find no evidence that the proportions of Bacteroidetes and Firmicutes among fecal bacteria have a function in human obesity.

The information superhijack.

Infection control teams are not alone in their need to manipulate data. How best can such manipulation be achieved and what tools are available to turn information into knowledge. The workshop included discussion and demonstration of some methods currently being used by infection control teams. While the workshop did not aim to produce all the answers, participants were able to question, discuss and learn new ways that they might take their own practice in the future.

Ethylene formation by cell-free extracts of Escherichia coli.

The pathway leading to the formation of ethylene as a secondary metabolite from methionine by Escherichia coli strain B SPAO has been investigated. Methionine was converted to 2-oxo-4-methylthiobutyric acid (KMBA) by a soluble transaminase enzyme. 2-Hydroxy-4-methylthiobutyric acid (HMBA) was also a product, but is probably not an intermediate in the ethylene-forming pathway. KMBA was converted to ethylene, methanethiol and probably carbon dioxide by a soluble enzyme system requiring the presence of NAD(P)H, Fe3+ chelated to EDTA, and oxygen. In the absence of added NAD(P)H, ethylene formation by cell-free extracts from KMBA was stimulated by glucose. The transaminase enzyme may allow the amino group to be salvaged from methionine as a source of nitrogen for growth. As in the plant system, ethylene produced by E. coli was derived from the C-3 and C-4 atoms of methionine, but the pathway of formation was different. It seems possible that ethylene production by bacteria might generally occur via the route seen in E. coli.

Ethylene formation by cultures of Escherichia coli.

Growth of Escherichia coli strain B SPAO on a medium containing glucose, NH4Cl and methionine resulted in production of ethylene into the culture headspace. When methionine was excluded from the medium there was little formation of ethylene. Ethylene formation in methionine-containing medium occurred for a brief period at the end of exponential growth. Ethylene formation was stimulated by increasing the medium concentration of Fe3+ when it was chelated to EDTA. Lowering the medium phosphate concentration also appeared to stimulate ethylene formation. Ethylene formation was inhibited in cultures where NH4Cl remained in the stationary phase. Synthesis of the ethylene-forming enzyme system was determined by harvesting bacteria at various stages of growth and assaying the capacity of the bacteria to form ethylene from methionine. Ethylene forming capacity was greatest in cultures harvested immediately before and during the period of optimal ethylene formation. It is concluded that ethylene production by E. coli exhibits the typical properties of secondary metabolism.