Mary Alice Smith

Comparison of six dose-response models for use with food-borne pathogens.

Food-related illness in the United States is estimated to affect over six million people per year and cost the economy several billion dollars. These illnesses and costs could be reduced if minimum infectious doses were established and used as the basis of regulations and monitoring. However, standard methodologies for dose-response assessment are not yet formulated for microbial risk assessment. The objective of this study was to compare dose-response models for food-borne pathogens and determine which models were most appropriate for a range of pathogens. The statistical models proposed in the literature and chosen for comparison purposes were log-normal, long-logistic, exponential, beta-Poisson and Weibull-Gamma. These were fit to four data sets also taken from published literature, Shigella flexneri, Shigella dysenteriae, Campylobacter jejuni, and Salmonella typhosa, using the method of maximum likelihood. The Weibull-gamma, the only model with three parameters, was also the only model capable of fitting all the data sets examined using the maximum likelihood estimation for comparisons. Infectious doses were also calculated using each model. Within any given data set, the infectious dose estimated to affect one percent of the population ranged from one order of magnitude to as much as nine orders of magnitude, illustrating the differences in extrapolation of the dose response models. More data are needed to compare models and examine extrapolation from high to low doses for food-borne pathogens.

Porphyromonas gingivalis Infection in Pregnant Mice Is Associated with Placental Dissemination, an Increase in the Placental Th1/Th2 Cytokine Ratio, and Fetal Growth Restriction

ABSTRACT Our previous animal studies showed that maternal Porphyromonas gingivalis infection in a subcutaneous chamber is associated with hepatic and uterine translocation, as well as systemic induction of maternal inflammatory responses, both of which were associated with fetal growth restriction (FGR). However, P. gingivalis-challenged dams had fetuses with either FGR (2 standard deviations below mean weight of nonchallenged dams) or normal weight. Therefore, the objective of this study was to determine whether maternal infection with P. gingivalis compromises normal fetal development via direct placental invasion and induction of fetus-specific placental immune responses characterized by a proinflammatory Th1-type cytokine profile. P. gingivalis-specific DNA was detected in placentas and fetuses of FGR and normal littermates from P. gingivalis-infected dams. Th1- and Th2-type cytokine mRNA as well as tumor necrosis factor alpha and transforming growth factor β2 mRNA were examined in placental tissue by using reverse transcription-PCR to determine Th1/Th2 ratios. For eight litters containing both normal-weight and FGR fetuses, P. gingivalis DNA was detected only in the placentas of FGR fetuses. All fetuses and all amniotic fluid samples from infected and control dams were negative for P. gingivalis DNA. mRNA levels of gamma interferon and interleukin-2 (IL-2) were significantly increased in placentas of FGR fetuses, while expression of IL-10 was significantly decreased in the same group. These data indicate that, in P. gingivalis-challenged dams, within each litter there is placenta-specific translocation of P. gingivalis that results in growth restriction of the targeted fetus, which is associated with a shift in the placental Th1/Th2 cytokine balance.

Preimplantation exposure to bisphenol A (BPA) affects embryo transport, preimplantation embryo development, and uterine receptivity in mice

To investigate the effects of bisphenol A (BPA) on embryo and uterine factors in embryo implantation, timed pregnant C57BL6 females were treated subcutaneously with 0, 0.025, 0.5, 10, 40, and 100mg/kg/day BPA from gestation days 0.5-3.5. In 100mg/kg/day BPA-treated females, no implantation sites were detected on day 4.5 but retention of embryos in the oviduct and delayed embryo development were detected on day 3.5. When untreated healthy embryos were transferred to pseudopregnant females treated with 100mg/kg/day BPA, no implantation sites were detected on day 4.5. In 40 mg/kg/day BPA-treated females, delayed implantation and increased perinatal lethality of their offspring were observed. Implantation seemed normal in the rest BPA-treated groups or the female offspring from 40 mg/kg/day BPA-treated group. These data demonstrate the adverse effects of high doses of BPA on processes critical for embryo implantation: embryo transport, preimplantation embryo development, and establishment of uterine receptivity.

Nonhuman Primate Model for Listeria monocytogenes-Induced Stillbirths

ABSTRACT Listeria monocytogenes, isolated from outbreaks in either human or nonhuman primate populations, was administered orally at doses ranging from 106 to 1010 CFU. Four of 10 treated animals delivered stillborn infants. L. monocytogenes was isolated from fetal tissue, and the pathology was consistent with L. monocytogenes infection as the cause of pregnancy loss. For all pregnancies resulting in stillbirths, L. monocytogenes was isolated from maternal feces, indicating that L. monocytogenes had survived and had probably colonized the gastrointestinal tract. Antibodies and antigen-specific lymphocyte proliferation against Listeria increased in animals that had stillbirths.

Dose-Response Model for Listeria monocytogenes-Induced Stillbirths in Nonhuman Primates

ABSTRACT A dose-response model using rhesus monkeys as a surrogate for pregnant women indicates that oral exposure to 107 CFU of Listeria monocytogenes results in about 50% stillbirths. Ten of 33 pregnant rhesus monkeys exposed orally to a single dose of 102 to 1010 CFU of L. monocytogenes had stillbirths. A log-logistic model predicts a dose affecting 50% of animals at 107 CFU, comparable to an estimated 106 CFU based on an outbreak among pregnant women but much less than the extrapolated estimate (1013 CFU) from the FDA-U.S. Department of Agriculture-CDC risk assessment using an exponential curve based on mouse data. Exposure and etiology of the disease are the same in humans and primates but not in mice. This information will aid in risk assessment, assist policy makers, and provide a model for mechanistic studies of L. monocytogenes-induced stillbirths.

Dose-Response of Listeria monocytogenes after Oral Exposure in Pregnant Guinea Pigs

Listeriosis, a severe disease that results from exposure to the foodborne pathogen Listeria monocytogenes, is responsible for approximately 2500 illnesses and 500 deaths in the United States each year. Pregnant women are 20 times more likely to develop listeriosis than the general population, with adverse pregnancy outcomes that include spontaneous abortions, stillbirths, and neonatal meningitis. The objective of this study was to determine an infective dose that resulted in stillbirths and infectivity of selected tissues in pregnant guinea pigs. Pregnant guinea pigs were exposed orally on gestation day 35 to 10(4) to 10(8) L. monocytogenes CFU in sterile whipping cream. L. monocytogenes was recovered at 64, 73, 90, and 100% from the livers of animals infected with 10(5), 10(6), 10(7), and 10(8) CFU, respectively. In dams exposed to > or =10(6) CFU, L. monocytogenes was cultured from 50% of the spleen samples and 33% of the gallbladder samples. Eleven of 34 dams infected with > or =10(6) CFU delivered stillborn pups. L. monocytogenes was cultured from the placenta, liver, and brain tissue of all stillbirths. Dams that delivered nonviable fetuses after treatment with > or =10(7) L. monocytogenes CFU had fecal samples positive for L. monocytogenes at every collection posttreatment. On the basis of a log-logistic model, the dose that adversely affected 50% of the pregnancies was approximately 10(7) L. monocytogenes CFU compared with that estimated from a human outbreak of 106 CFU. Listeriosis in pregnant guinea pigs can result in stillbirths, and the overall disease is similar to that described in nonhuman primates and in humans.

The key events dose-response framework: its potential for application to foodborne pathogenic microorganisms.

The Key Events Dose-Response Framework (KEDRF) is an analytical approach that facilitates the use of currently available data to gain insight regarding dose-response relationships. The use of the KEDRF also helps identify critical knowledge gaps that once filled, will reduce reliance on assumptions. The present study considers how the KEDRF might be applied to pathogenic microorganisms, using fetal listeriosis resulting from maternal ingestion of food contaminated with L. monocytogenes as an initial example. Major biological events along the pathway between food ingestion and the endpoint of concern are systematically considered with regard to dose (i.e., number of organisms), pathogen factors (e.g., virulence), and protective host mechanisms (e.g., immune response or other homeostatic mechanisms). It is concluded that the KEDRF provides a useful structure for systematically evaluating the complex array of host and pathogen factors that influence the dose-response relationship. In particular, the KEDRF supports efforts to specify and quantify the sources of variability, a prerequisite to strengthening the scientific basis for food safety decision making.

Comparison of Listeria monocytogenes virulence in a mouse model.

Listeriosis results from exposure to the foodborne pathogen Listeria monocytogenes. Although many different strains of L. monocytogenes are isolated from food, no definitive tests currently predict which isolates are most virulent. The objectives of this study were to address two major data gaps for risk assessors, variability among L. monocytogenes strains in pathogenicity and virulence. Strains used in our monkey clinical trial or additional food isolates were evaluated for their virulence and infectivity in mice. All strains were equally pathogenic to immunocompromised mice, causing deaths to 50% of the population 3 days after exposure to doses ranging from 2 to 3 log CFU. Doses resulting in 50% deaths on the fifth day after administration were 1 to 2 log lower than those on the third day, indicating that the full course of pathogenicity exceeds the 3-day endpoint in immunocompromised mice. Three strains were chosen for further testing for their virulence and infectivity in liver and spleen in normal (immunocompetent) mice. Virulence was not significantly different (P > 0.05) among the three strains, all resulting in deaths to 50% of mice at 5 to 7 log CFU by 5 days after administration. All strains were equally infective in liver or spleen, with higher numbers of L. monocytogenes directly correlated with higher doses of administration. In addition, there was no preference of organs by any strains. The lack of strain differences may reflect the limitation of the mouse model and suggests the importance of using various models to evaluate the pathogenicity and virulence of L. monocytogenes strains.

Risk of Fetal Mortality After Exposure to Listeria monocytogenes Based on Dose-Response Data from Pregnant Guinea Pigs and Primates

One-third of the annual cases of listeriosis in the United States occur during pregnancy and can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn. Previous risk assessments completed by the Food and Drug Administration/the Food Safety Inspection Service of the U.S. Department of Agriculture/the Centers for Disease Control and Prevention (FDA/USDA/CDC) and Food and Agricultural Organization/the World Health Organization (FAO/WHO) were based on dose-response data from mice. Recent animal studies using nonhuman primates and guinea pigs have both estimated LD(50)s of approximately 10(7) Listeria monocytogenes colony forming units (cfu). The FAO/WHO estimated a human LD(50) of 1.9 x 10(6) cfu based on data from a pregnant woman consuming contaminated soft cheese. We reevaluated risk based on dose-response curves from pregnant rhesus monkeys and guinea pigs. Using standard risk assessment methodology including hazard identification, exposure assessment, hazard characterization, and risk characterization, risk was calculated based on the new dose-response information. To compare models, we looked at mortality rate per serving at predicted doses ranging from 10(-4) to 10(12) L. monocytogenes cfu. Based on a serving of 10(6) L. monocytogenes cfu, the primate model predicts a death rate of 5.9 x 10(-1) compared to the FDA/USDA/CDC (fig. IV-12) predicted rate of 1.3 x 10(-7). Based on the guinea pig and primate models, the mortality rate calculated by the FDA/USDA/CDC is underestimated for this susceptible population.

Setting research priorities to improve global newborn health and prevent stillbirths by 2025

Background In 2013, an estimated 2.8 million newborns died and 2.7 million were stillborn. A much greater number suffer from long term impairment associated with preterm birth, intrauterine growth restriction, congenital anomalies, and perinatal or infectious causes. With the approaching deadline for the achievement of the Millennium Development Goals (MDGs) in 2015, there was a need to set the new research priorities on newborns and stillbirth with a focus not only on survival but also on health, growth and development. We therefore carried out a systematic exercise to set newborn health research priorities for 2013–2025. Methods We used adapted Child Health and Nutrition Research Initiative (CHNRI) methods for this prioritization exercise. We identified and approached the 200 most productive researchers and 400 program experts, and 132 of them submitted research questions online. These were collated into a set of 205 research questions, sent for scoring to the 600 identified experts, and were assessed and scored by 91 experts. Results Nine out of top ten identified priorities were in the domain of research on improving delivery of known interventions, with simplified neonatal resuscitation program and clinical algorithms and improved skills of community health workers leading the list. The top 10 priorities in the domain of development were led by ideas on improved Kangaroo Mother Care at community level, how to improve the accuracy of diagnosis by community health workers, and perinatal audits. The 10 leading priorities for discovery research focused on stable surfactant with novel modes of administration for preterm babies, ability to diagnose fetal distress and novel tocolytic agents to delay or stop preterm labour. Conclusion These findings will assist both donors and researchers in supporting and conducting research to close the knowledge gaps for reducing neonatal mortality, morbidity and long term impairment. WHO, SNL and other partners will work to generate interest among key national stakeholders, governments, NGOs, and research institutes in these priorities, while encouraging research funders to support them. We will track research funding, relevant requests for proposals and trial registers to monitor if the priorities identified by this exercise are being addressed.