A pilot study for the intrinsic labeling of egg proteins with 15N and 13C.

The aim of this study was to produce intrinsically and uniformly doubly (15)N-(13)C-labeled proteins. These proteins can be used as intrinsic tracers of dietary amino acids, both α-amino groups and carbon skeletons, during postprandial metabolic utilization. Two (Rhodes) laying hens were fed for 16 days with a standard poultry diet supplemented with 0, 0.2% or 0.4% of a mixture of 20 doubly (15)N-(13)C-labeled AAs. A third hen was given a non-enriched diet, as the control. The eggs laid were collected over 24 days, from 3 days before to 4 days after supplementation. The (15)N and (13)C enrichments in proteins from white and yolk were measured by EA-IRMS and GC-C-IRMS for enrichment in individual amino acids. After 10 days of supplementation, the (15)N enrichment reached an isotopic plateau at 1500 to 3000 ‰, depending on the supplementation level, in both white and yolk while the (13)C enrichment was 220 to 650 ‰ in white and was 100 to 250 ‰ in yolk. The (15)N enrichment was similar among the amino acids, except for the aromatic ones in which the enrichment was lower. The δ(13)C values were variable among amino acids in both white and yolk, ranging from 77 ‰ for tyrosine to 555 ‰ for proline with the 0.2 % supplementation level. In conclusion, the incorporation of 0.2 % labeled amino acids in the hen diet allowed us to achieve sufficient enrichment for metabolic studies. However, due to the non-homogeneity of the (13)C labeling, adequate (13)C enrichment of individual amino acids must be considered depending on the investigated metabolic pathway.

Impact of residual and therapeutic doses of ciprofloxacin in the human-flora-associated mice model.

A study was conducted to evaluate the effects of therapeutic and residual doses of ciprofloxacin on the human intestinal flora implanted into germ-free mice. Ciprofloxacin was administered daily via drinking water at concentrations to provide doses of 0, 0.125, 1.25, and 12.5mg/kg b.w. Changes in the intestinal flora composition, alteration in bacterial enzyme activities, fecal short chain fatty acid concentration and bacterial cellular fatty acid profiles, overgrowth of resistant bacteria, and disruption of the colonization barrier were the endpoints evaluated in the feces of human-flora-associated (HFA) mice. Ciprofloxacin at all tested doses decreased significantly the aerobic populations and particularly the population of Enterobacteriaceae. Selection of resistant Bacteroides fragilis group was noticed in HFA mice receiving 12.5mg/kg b.w. In mice challenged with a Salmonella strain, exogenous Salmonella persisted in the feces of all treated mice indicating that the flora responsible for the colonization barrier effect was disturbed by the antibiotic treatment. None of the studied metabolic parameters of the flora were affected by ciprofloxacin at any dose level. Under the experimental conditions of the study, the no-observed-effect level of ciprofloxacin was found to be less than 0.125 mg/kg b.w.