Fitness-for-purpose of dietary survey duration: a case-study with the assessment of exposure to ochratoxin A.

The duration of food consumption survey may have a marked effect on estimates of usual nutrient intakes in individuals and groups. This arises from a high degree of within-person variability in food intakes, primarily on a day-to-day basis. Both the level of observation-populations versus individuals-and the desirable level of precision decide upon the 'fitness-for-purpose' of dietary survey duration. Though similar from a methodological standpoint, the question was rarely addressed in the case of non-nutrients. Our work aims at estimating the number of days of food records needed for the assessment of usual intakes of food chemicals as a function of research purpose. Focusing on the French population exposure to food mycotoxin ochratoxin A, we implement a range of well-established methods borrowed from the field of nutrient intakes assessment. Our results on OTA show that: (a) at the population level, as low as three days give satisfactory distributional estimates; yet, the implementation of variance reduction methods is of particular relevance when higher percentiles of exposure are at stake; (b) the estimation of individual usual intakes based on food records is behind practical possibilities, which calls for alternative options such as biomarkers of exposure.

Study through surveys and fermentation kinetics of the traditional processing of pearl millet (Pennisetum glaucum) into ben-saalga, a fermented gruel from Burkina Faso.

Traditional cereal-based fermented foods are frequently used as complementary foods for infants and young children in Africa. This is the case for ben-saalga, a popular fermented gruel produced from pearl millet (Pennisetum glaucum) in Burkina Faso. Detailed knowledge of traditional processing is a prerequisite for investigating ways to improve both the nutritional and sanitary qualities of the corresponding foodstuff. In this work, the traditional processing of pearl millet into ben-saalga was investigated in 24 production units, and fermentation kinetics were studied in pilot scale experiments. Processing steps include: washing (optional), soaking of the grains (first fermentation step), grinding and sieving of the wet flour, settling (second fermentation step), and cooking. The soaking step was mainly characterized by alcoholic fermentation whereas lactic acid fermentation occurred during the settling step. Fermentation kinetics during settling indicates a temporal variation of metabolic activity. Initially, both homofermentative and heterofermentative pathways were simultaneously active, and later only a homofermentative pathway was active. The paste produced at the end of settling had a low pH (4.0+/-0.4) and its microflora was dominated by lactic acid bacteria (LAB) with an amylolytic LAB/LAB ratio of 12%. Sucrose disappeared in the grains during soaking but was not detected in the soaking water, whereas glucose, fructose and maltose appeared transiently. Glucose and fructose were the main substrates observed for lactic acid fermentation during the settling step; however unbalanced fermentation led to the hypothesis that starch hydrolysis products may also serve as substrates for lactic acid formation. At the end of the processing, a 75% and 83% decrease was observed in phytate (IP6) and raffinose, respectively. The sour gruel ben-saalga resulting from cooking the sour paste had inadequate nutritional characteristics with respect to infants' and young children's requirements; it was characterized by fluid consistency (Bostwick flow: 137 mm/30 s) and low energy density (about 30 kcal/100 g of gruel).

Some recent advances in modelling dietary exposure to ochratoxin A.

One of the key questions when assessing the exposure to contaminants is the choice of the method and the impact of this choice on the result to be compared with the toxicological reference value. This problem is particularly significant in the case of ochratoxin A (OTA) for which the use of crude estimates can provide results close to the current provisional tolerable weekly intake (PTWI). This paper compares different exposure assessment models for OTA using the same data set for food consumption (i.e. French INCA survey 1999) for the same groups of the population (i.e. adults excluding under-reporters and children 3-14 years-old) but with various ways of handling the occurrence of OTA in food. The consumption and contamination data were combined through 11 different scenarios based on parametric and non-parametric modelling and on the use of analytical results obtained on raw commodities or on foodstuffs ready-to-eat. In order to assess exposure to OTA using data on consumption of processed and composite foods it was necessary to use recipe information in order to utilize available contamination data which only exists for raw materials. The impact of such an adjustment appears to be essential to avoid an overestimation of the exposure. The impact of the other assumptions and the choice of mathematical models influence the results less but should be considered and detailed carefully in future dietary exposure assessments.

Handling of contamination variability in exposure assessment: a case study with ochratoxin A.

The contamination of foods dedicated to human consumption varies over space and time. In exposure assessment, this is usually addressed through probabilistic modelling. The present work explores how the variability and uncertainty of exposures estimated at the population level are affected by: (a) the (non-)parametric nature of input contamination distributions; (b) the time-window used to sample contamination values within those distributions. Focusing on exposure of the French population to food mycotoxin ochratoxin A, we implement a range of second-order Monte-Carlo simulations that allow distinguishing variability of exposures from uncertainty of distributional parameters estimates. A simulation runs 10,000 iterations. Overall estimates of parameters are given by the median across iterations and 95%CI by 2.5th and 97.5th percentiles. Our results show that: (a) parametric (log-normal) input distributions may lead to over-estimation of variability and greater uncertainty as compared to non-parametric ones (P97.5 [95%CI] of 7.1 [6.6;7.7] for Parametric-Occasion, 4.6 [4.3;5.0] for Non-Parametric-Occasion), and that (b) the 'Occasion' time-window combines better estimate of variability and lower uncertainty when exposure modelling is applied to populations living in developed countries with complex agri-food systems (P97.5 [95%CI]: 7.3 [6.2;8.9] for Non-Parametric-Week, 4.6 [4.3;5.0] for Non-Parametric-Occasion). A deterministic approach is nevertheless preferred to probabilistic modelling every time input data quality is questionable.

agr expression precedes escape of internalized Staphylococcus aureus from the host endosome.

Staphylococcus aureus is a versatile pathogen capable of causing life-threatening infections. Many of its cell wall and exoproduct virulence determinants are controlled via the accessory gene regulator (agr). Although considered primarily as an extracellular pathogen, it is now recognized that S. aureus can be internalized by epithelial and endothelial cells. Traditional experimental approaches to investigate bacterial internalization are extremely time-consuming and notoriously irreproducible. We present here a new reporter gene method to assess intracellular growth of S. aureus in MAC-T cells that utilizes a gfp-luxABCDE reporter operon under the control of the Bacillus megaterium xylA promoter, which in S. aureus is expressed in a growth-dependent manner. This facilitates assessment of the growth of internalized bacteria in a nondestructive assay. The dual gfp-lux reporter cassette was also evaluated as a reporter of agr expression and used to monitor the temporal induction of agr during the MAC-T internalization process. The data obtained suggest that agr induction occurs prior to endosomal lysis and that agr-regulated exoproteins appear to be required prior to the release and replication of S. aureus within the infected MAC-T cells.