Dose Response of Listeria monocytogenes Invasion, Fetal Morbidity, and Fetal Mortality after Oral Challenge in Pregnant and Nonpregnant Mongolian Gerbils

Abstract

ABSTRACTListeria monocytogenesis a food-borne pathogen that can result in adverse pregnancy outcomes, such as stillbirth or premature delivery. The Mongolian gerbil was recently proposed as the most appropriate small-animal model of listeriosis due to its susceptibility to the same invasion pathways as humans. The objectives of this study were to investigate invasion and adverse pregnancy outcomes in gerbils orally exposed toL. monocytogenes, to compare the dose-response data to those of other animal models, and to investigate differences in the responses of pregnant versus nonpregnant gerbils. Gerbils were orally exposed to 0 (control), 103, 105, 107, or 109CFUL. monocytogenesin whipping cream.L. monocytogeneswas recovered in a dose-dependent manner from fecal samples, adult organs, and pregnancy-associated tissues. Dams exposed to 109CFU had more invaded organs and higher concentrations ofL. monocytogenesin almost all organs than nonpregnant animals, though no differences in fecal shedding were seen between the two groups. Adverse pregnancy outcomes occurred only in the dams treated with 109CFU. A 50% infectivity dose (ID50) of 2.60 × 106CFU for fetuses was calculated by fitting the data to a logistic model. Our results suggest that the 50% lethal dose (LD50) falls within the range of 5 × 106to 5 × 108CFU. This range includes the guinea pig and nonhuman primate LD50s, but the observation thatL. monocytogenes-induced stillbirths can be seen in guinea pigs and primates exposed to lower doses than those at which stillbirths were seen in gerbils indicates that gerbils are not more sensitive toL. monocytogenesinvasion.