Dose Response of Listeria Monocytogenes in Pregnant Guinea Pigs for Use in Risk

APPROACH: Preliminary experiments will determine the L. monocytogenes strain, dose range, and endpoints for the full dose response study. Pregnant guinea pigs will be treated with three outbreak strains of L. monocytogenes, having known virulence in mouse and non-human primate studies, by oral gavage. Animals will be handled in accordance with the National Institutes of Health and Animal Welfare Act guidelines. The strain that is the most virulent in the preliminary studies will be used for the range-finding study. Next, three different doses of the most virulent strain will be given to groups of three pregnant guinea pigs. The pregnancies will be monitored while enumerating levels of L. monocytogenes in fecal materials. The animals will be sacrificed, and tissues collected from maternal liver, maternal spleen, placentas, and fetuses. After examining fecal shedding data, pregnancy outcome and L. monocytogenes counts in maternal tissues, endpoints and doses will be chosen for the full dose response experiment. This experiment will be done by treating pregnant guinea pigs with L. monocytogenes at four doses plus a broth control. Experimental endpoints will include fetal viability or abortion, fetal weight, and culturable L. monocytogenes from maternal liver, spleen, placenta and fetus. The data collected for these experiments will be used to model a dose response curve for guinea pigs. This dose response curve will be compared to the dose response curve now being developed for a non-human primate study and to the dose response curves in the FSIS/FDA risk assessment. Several different dose response models will be used to determine the best fit for the guinea pig data including the Weibull-gamma, beta-Poisson and the log logistic.
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PROGRESS: 2003/09 TO 2006/09<BR>
Progress Report Objectives (from AD-416) The overall objective of the research is to use pregnant guinea pigs to develop additional dose response information for L. monocytogenes-induced human stillbirths or abortions. The specific objectives are to: 1) conduct a range-finding experiment to determine the region of dose response overlap with the existing non-human primate study, 2) determine the dose response for adverse fetal effect after maternal exposure to L. monocytogenes, particularly low dose exposures resulting in 10-20% fetal illness or death, and determine endpoints that predict adverse pregnant outcome such as L. monocytogenes invasion of maternal liver, maternal spleen, placenta and fetus, and 3) compare the dose response curve developed in pregnant guinea pigs to mouse, primate and human dose response curves, and evaluate the guinea pig as a surrogate model for humans. Approach (from AD-416) Preliminary experiments will determine the L. monocytogenes strain, dose range, and endpoints for the full dose response study. Pregnant guinea pigs will be treated with three outbreak strains of L. monocytogenes, having known virulence in mouse and non-human primate studies, by oral gavage. Animals will be handled in accordance with the National Institutes of Health and Animal Welfare Act guidelines. The strain that is the most virulent in the preliminary studies will be used for the range-finding study. Next, three different doses of the most virulent strain will be given to groups of three pregnant guinea pigs. The pregnancies will be monitored while enumerating levels of L. monocytogenes in fecal materials. The animals will be sacrificed, and tissues collected from maternal liver, maternal spleen, placentas, and fetuses. After examining fecal shedding data, pregnancy outcome and L. monocytogenes counts in maternal tissues, endpoints and doses will be chosen for the full dose response experiment. This experiment will be done by treating pregnant guinea pigs with L. monocytogenes at four doses plus a broth control. Experimental endpoints will include fetal viability or abortion, fetal weight, and culturable L. monocytogenes from maternal liver, spleen, placenta and fetus. The data collected for these experiments will be used to model a dose response curve for guinea pigs. This dose response curve will be compared to the dose response curve now being developed for a non-human primate study and to the dose response curves in the FSIS/FDA risk assessment. Several different dose response models will be used to determine the best fit for the guinea pig data including the Weibull-gamma, beta-Poisson and the log logistic. Significant Activities that Support Special Target Populations 1935-42000-057-02G - This report serves to document research conducted under a General Assistance Type of agreement between ARS and the University of Georgia. The doses of L. monocytogenes that result in human listeriosis were not known, primarily because human experimental studies cannot be conducted. Researchers at the University of Georgia and the ARS Eastern Regional Research Center in Wyndmoor, PA used pregnant guinea pigs to develop dose response information for L. monocytogenes-induced human stillbirths and/or abortions. This was done by 1) determining the region of dose-response overlap with the existing non-human primate study, 2) determining the dose-response for adverse fetal effect after maternal exposure to L. monocytogenes, 3) defining endpoints that predict adverse pregnant outcomes such as L. monocytogenes invasion of maternal liver, maternal spleen, placenta and fetus, and 4) comparing the dose response curve developed in pregnant guinea pigs to mouse, primate and human dose response curves. This research supported the Project plan by producing dose response models that more accurately estimate infective doses of L. monocytogenes. The monitoring activities included phone calls and receipt of written reports.