Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ontario, Canada; Human Health Therapeutics, Division of Life Sciences, National Research Council of Canada, Ottawa, Ontario, Canada.
Placenta. 2019 Aug;83:43-52. doi: 10.1016/j.placenta.2019.06.386. Epub 2019 Jun 26.
Salmonella species are gram-negative facultative intracellular bacteria that are common causes of foodborne illness in North America. Infections by Salmonella during pregnancy are a significant cause of fetal loss in domestic livestock, and fetal and maternal mortality in mice. Furthermore, Salmonella infection is associated with miscarriage, stillbirth and preterm birth in pregnant women. Despite these collective associations, the extent to which Salmonella can infect the human placenta has not been investigated.
Human placental villous explants from several gestational ages were exposed to Salmonella enterica serovar Typhimurium (STm) ex vivo. Infection was assessed by colony forming unit assay and whole mount immunofluorescence (WMIF).
Viable bacteria were recovered from placental villous explants of all gestational ages tested, but the bacterial burden was highest in 1st trimester explants. Bacterial numbers did not change appreciably with time post-infection in explants from any gestational age examined, suggesting that STm does not proliferate in placental villi. Exposure of villous explants to STm strains defective for the type III secretion systems revealed that Salmonella pathogenicity island 1 is essential for optimal invasion. In contrast to placental explants, STm infected and proliferated within villous cytotrophoblast cells isolated from term placentas. WMIF demonstrated that STm was restricted primarily to the syncytiotrophoblast layer in infected placentas.
Our study demonstrates that STm can invade into the syncytiotrophoblast but does not subsequently proliferate. Thus, the syncytiotrophoblast may function as a barrier to STm infection of the fetus.
沙门氏菌属是革兰氏阴性兼性细胞内细菌，是北美的常见食源性疾病病原体。怀孕期间沙门氏菌感染是家畜胎儿流产的重要原因，也是老鼠胎儿和母体死亡的原因。此外，沙门氏菌感染与孕妇流产、死产和早产有关。尽管存在这些关联，但沙门氏菌感染人类胎盘的程度尚未得到研究。
来自多个妊娠阶段的人胎盘绒毛外植体进行了沙门氏菌 Typhimurium (STm) 的离体暴露。通过集落形成单位测定和全培养免疫荧光（WMIF）评估感染情况。
从所有测试妊娠阶段的胎盘绒毛外植体中均回收了存活细菌，但在 1 期外植体中的细菌负荷最高。在任何检查的妊娠阶段的外植体中，感染后细菌数量没有明显随时间变化，表明 STm 在胎盘绒毛中不会增殖。对 STm 菌株的 III 型分泌系统缺陷的绒毛外植体的暴露表明，沙门氏菌致病岛 1 对于最佳入侵是必需的。与胎盘外植体相反，STm 在从足月胎盘分离的绒毛滋养细胞中感染和增殖。WMIF 表明 STm 在感染的胎盘内主要局限于合胞滋养层层。
我们的研究表明，STm 可以侵入合胞滋养层，但随后不会增殖。因此，合胞滋养层可能是 STm 感染胎儿的屏障。
