Pregnant goats were inoculated intravenously or in uterine arteries with Brucella abortus, and tissues from the uterus and placenta were examined by electron microscopy. Identification of B. abortus in placentae was with antibody-coated colloidal gold. B. abortus was first seen in phagosomes of erythrophagocytic trophoblasts and in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Subsequently, trophoblast necrosis and ulceration of chorioallantoic membranes were present. Coincidently, B. abortus was present in the lumen of placental capillaries. In late stages of infection, placental vasculitis was present, and placentomal trophoblasts were separated from maternal syncytial epithelium. In lesions with vasculitis, large numbers of B. abortus were in connective tissue of chorionic villi. Within the placentome, trophoblasts that lined chorionic villi contained no intracellular bacteria and were separated from B. abortus by intact basement membranes. These results suggest that bacteremic B. abortus is endocytosed by erythrophagocytic trophoblasts and that B. abortus replicates in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Replication of brucellae in trophoblastic rough endoplasmic reticulum is unique; we believe that B. abortus may utilize endoplasmic reticulum for synthesis and glycosylation of bacterial membrane proteins or that B. abortus catabolizes trophoblast secretory proteins.
Abstract. Pregnant goats were given Brucella abortus intravenously or in uterine arteries, and tissues from the uterus and placentae were examined at various post-inoculation intervals to study mechanisms of placental infection. Placentitis was present by 5 days post-inoculation and abortions occurred within 11 days. B. abortus was identified in placentae by light microscopy and immunoperoxidase techniques. B. abortus was first seen in erythrophagocytic trophoblasts of the placentome. Subsequently, high numbers of B. abortus were seen in periplacentomal chorioallantoic trophoblasts. Trophoblast necrosis, chorioallantoic ulceration, and large numbers of B. abortus in chorionic villi were present in later stages of infection. These results suggest that entry and replication of B. abortus in trophoblasts precede placentome and fetal infection and that trophoblasts are the source of B. abortus for these tissues. Experimental caprine brucellosis closely resembles bovine and ovine brucellosis and it provides a model to study the intracellular development of B. abortus in trophoblasts.Brucella abortus has a marked predilection for the ruminant placenta. In acute infections of pregnant cows, up to 85% of the bacteria are in cotyledons, placental membranes, and allantoic fluid. Materials and MethodsTwenty 2-to 3-year-old pregnant alpine crossbred goats in their last third of gestation were given various amounts of Brucella abortus (strain 2308 supplied by Dr. B. Deyoe, National Animal Disease Center, Ames, IA) in jugular veins, uterine arteries, or the uterine lumen (Tables 1, 2). Goats were maintained in isolation until necropsy. Four pregnant goats were not inoculated and served as controls. All goats lacked serum antibodies to B. abortus (card and tube agglutination test) and no clinical evidence of brucellosis was apparent in the herd history.Jugular vein inoculations were done by injecting varying amounts of B. abortus into either the right or left jugular vein (Table 1). Uterine artery inoculations were done following ventral laporatomy on goats anesthetized with 2 to 4 mg/kg ketamine hydrochloride (Ketaset, Bristol Laboratories, Syracuse, NY) and 0.1 mg/kg xylazine (Rompun, Haver-Lockhart, Shawnee, KS). Gravid uteri were removed from the abdomen, the middle uterine arteries were exposed, and various amounts of B. abortus (Table 1) suspended in phosphate buffered saline were injected into one or both species. One goat was inoculated into the uterine lumen with lo6 B. abortus after an unsuccessful attempt at inoculating the uterine artery. At first, random dosages were selected to evaluate the effect of dose upon lesion development. Later, most goats received lo9 B. abortudml of diluent (Tables 1, 2). All goats appeared clinically normal after inoculations and were observed twice daily until necropsy.Goats were necropsied from 2 to 23 days post-inoculation. At necropsy, gravid uteri were exposed by ventral laparot-219
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