Effects of Shiga toxin type 2 in rats in the late stage of pregnancy.

BURDET JULIA; ZOTTA ELSA; FRANCHI ANA MARÍA; IBARRA CRISTINA

Buenos Aires

Simposio; VTEC2009: 7th International Symposium on Shiga Toxin (Verocytotoxin)-producing Escherichia coli infections.; 2009

Asociación Argentina de Microbiología

Maternal infections have been linked to several adverse pregnancy outcomes in humans, including fetal anomalies, intrauterine fetal death, premature labor, premature rupture of the membranes, and abortion. There is only one case report of Shiga toxin-producing Escherichia coli (STEC) infection in pregnancy. Although this patient delivered a normal baby at term, whether STEC infections affect pregnant women has not yet been established. The main virulence factor of STEC is Shiga toxin type 1 or 2 (Stx1, Stx2), although strains that express only Stx2 are highly prevalent. The glycolipid globotriaosylceramide (Gb3) is the functional receptor for Stx found on the surface of target cells. Stx is internalized into the cell causing cellular death. Objective In this study, we evaluated the effect of Stx2 on maternal lethality, fetal status and delivery time by injecting Stx2 in rats in the late stage of pregnancy. Methods Pregnant rats on days 14-16 of gestation and non-pregnant rats were injected intraperitoneally with filtered culture supernatant of recombinant E. coli containing 0.4 pg/ml of crude Stx2. Aliquots of 0.1 to 4.0 ml (0.15-6 ng of Stx2/g body weight) were assayed. Maternal survival and development of preterm labor were evaluated at different times. Fertility of the surviving rats was determined 22 ± 3 days post-injection. A group of pregnant rats were injected with the 50% lethal dose (LD50) of non-pregnant rats (2 ng Stx2/g body weight) and were killed on day 2 post-injection. Fetus, placenta, uterus and kidney were used for histological and immunohistochemical studies. Results Stx2 induced fetoplacental resorption, placental abruption, intrauterine hemorrhage and fetal death at 1-2 days post-injection in a dose-dependent manner. At 2 ng Stx2/g body weight, placentas and fetuses presented extensive necrosis areas, while uteri and kidneys showed normal histology. Immunolocalization of Gb3 was observed in placentas, fetuses and uteri in the same areas where Stx2 binding was detected. Staining for inducible nitric oxide synthase (iNOS) in the feto-maternal unit was higher in treated rats than in non-treated rats. Survival of pregnant rats treated with Stx2 was higher than that of non-pregnant rats treated with the same doses. All surviving rats were able to become pregnant and deliver normal pups at term. Conclusion Our results show, for the first time, that the preterm labor observed in treated rats may be a consequence of Stx2 action on the feto-maternal unit. Although there are no reports of Stx2-mediated fetal damage or fetal death in humans, we speculate that STEC infections during pregnancy could be detrimental to the fetus. However, pregnancy could have a protective effect against Stx2 damage in mothers. Further experiments are in process to understand the mechanism involved in the development of the preterm labor caused by Stx2 in pregnant rats and the protection observed in the mother after Stx2-treatment. Key words: Preterm labor, Stx2 infection, pregnancy, maternal survival