Intracellular Localization of Brucella abortus in Bovine Placenta

Abstract

Invasion of the gravid bovine uterus by Brucella abortus often leads to placentitis and abortion. Within the placenta, brucellae replicate to high numbers in the trophoblastic epithelium. 1.7.8 Minimal degenerative changes in brucellae-filled trophoblasts suggest a unique bacterium-host cell relationship. In experimentally infected goats* and in chick embryo^,^ B. abortus replicates in the rough endoplasmic reticulum (RER) of trophoblasts and in nonphagocytic cells, respectively. Localization in the RER is unique among bacterial pathogens and may be critical for replication of B. abortus in certain tissues and in the pathogenesis of bovine brucellosis. Before this host-parasite relationship is further investigated, it is necessary to determine if B. abortus replicates in the RER of trophoblasts in the natural host. In this study, we report the intracellular location of B. abortus in the gravid bovine uterus as determined by immunohistochemical and electron microscopic examination.Six cows in midgestation were infected topically onto the conjunctivae by instillation of 1 x lo7 or 1 x lo8 organisms of B. abortus strain 2308. Cows were euthanatized with intravenous pentobarbital at 199 to 253 days of gestation (36 to 80 days post-exposure). Time of necropsy was based on onset of premature delivery. Brucella abortus was isolated from uterine exudate, chorioallantoic placenta, and fetal tissues by direct smears of tissues onto tryptose agar from all cows. For light microscopic examination, tissues from placenta and uterus were fixed for 24 hours in 10% neutral buffered formalin, processed by routine paraffin embedding techniques, sectioned, and stained with hematoxylin and eosin and a Brucella-specific avidin-biotin irnmunoperoxidase technique.6 Tissues from placenta and placentomes were fixed in 2.5% glutaraldehyde in 1.0 M cacodylate buffer and processed, and thin sections were stained with uranyl acetate and lead citrate and examined with transmission electron microscopy (Philips 4 10).Microscopic lesions were moderate to severe in all cows. Purulent exudate containing intra-and extracellular brucellae was in the inter-and periplacentomal uterochorionic spaces and at the base of cotyledonary villi. Chorioallantoic membranes had marked edema, several macrophages and neutrophils in the interstitium, segmental fibrinous vasculitis, and multifocal erosion of periplacentomal chorionic epithelium. Trophoblasts lining the base of cotyledonary villi and periplacentomal regions were filled with brucellae (Fig. 1). Numbers of infected trophoblasts varied among placentomes collected from the same cow; there were individual to confluently infected trophoblasts. In three cows, brucellae were present in neutrophils and macrophages and were also present extracellularly in the placental interstitium. Large colonies of extracellular brucellae were in the interstitium and capillary lumens in the chorionic villi of one cow (Fig. 2). Brucellar antigen was most abundant in trophoblasts; lesser quantities were in phagocytic cells and w...

Differential Requirements for VirB1 and VirB2 during Brucella abortus Infection

“…The importance of these genes for intracellular survival was demonstrated in tissue culture models of infection as well (12,15,20,24,30). These genes were subsequently found to be expressed intracellularly by Brucella suis in macrophages (8), where they are required for localization of B. abortus to an intracellular niche that is associated with the endoplasmic reticulum (9), the same location where B. abortus was earlier shown to replicate in nonprofessional phagocytes (13,14,27) and in the ruminant placenta (2,23). For B. abortus, the virB genes have been implicated in the initial interactions between the bacterium and the host cell during entry into macrophages (33).…”

Brucella abortus Rough Mutants Induce Macrophage Oncosis That Requires Bacterial Protein Synthesis and Direct Interaction with the Macrophage

“…In addition, the bacteria infect a variety of nonprofessional phagocytes, including NIH 3T3, HeLa, Vero, DMCK, and BHK cells (50). The bacteria also invade trophoblast cells and cause abortion in ruminants (5,45). It is well accepted that survival of Brucella in host macrophages determines virulence and contributes to disease pathogenesis (41).…”

Production of the Siderophore 2,3-Dihydroxybenzoic Acid Is Required for Wild-Type Growth of Brucella abortus in the Presence of Erythritol under Low-Iron Conditions In Vitro

“…Pregnant cattle exhibit the greatest sensitivity to infection by B. abortus, and susceptibility to the disease increases as pregnancy progresses. Abortion is associated with the extensive replication of the brucellae within the chorioallantoic trophoblasts that form a vital component of the placenta (1,15,29,31). This massive intracellular replication ruptures the infected trophoblasts and allows the bacteria direct access to the fetus (20).…”