Bacterium Brucella Abortus Research Articles

B Lymphocytes Provide an Infection Niche for Intracellular Bacterium Brucella abortus

Brucella spp. are intracellular bacteria that establish lifelong infections whose mechanisms of chronicity are poorly understood. Notably, B cells facilitate the establishment of the high infection plateau that persists for months. We evaluated the contribution of murine B cells toward providing infection niches for Brucella by using flow cytometry and microscopy and by determining live bacterial counts associated with B cells both in vivo and in vitro. Herein we demonstrate that immunoglobulin M and complement-opsonized Brucella abortus infects and survives inside primary murine B cells protected from bactericidal effects of gentamicin. The entry was dependent on microfilaments for internalization and subsequently brucellae reside in a late endosomal/lysosomal compartment. Throughout the infection, 10% of colony-forming units from infected mice was associated with B cells, and these cells transferred disease to naive hosts. Furthermore, Brucella-positive cells were positive for transforming growth factor (TGF) β1, and about 10% of such cells were B cells, similar to rates found for other intracellular pathogens that induce their hosts cells to produce TGF-β1. To conclude, infected B cells contribute to chronic bacterial infections by providing an intracellular niche that may exert an immunoregulatory role. Although professional phagocytic cells harbor intracellular bacteria including Brucella, infection of lymphocytes by bacteria has not been previously appreciated.

Seroprevalence of Neospora caninum and Brucella abortus in Dairy Cattle Herds with High Abortion Rates

The protozoan Neospora caninum and the bacterium Brucella abortus are well-recognized causes of abortion in dairy cattle. Serum samples (n = 240) from aborting (n = 141) and at-risk (n = 99) animals from 5 herds with high abortion rates in Punjab Province, Pakistan, were tested for antibodies to N. caninum using monoclonal antibody-based ELISA and for antibodies to B. abortus using the serum agglutination test. Antibodies to N. caninum and B. abortus were detected in 105 (43.8%) and 135 (56.3%) cattle, respectively. Prevalences of antibodies to N. caninum and B. abortus were higher in aborting cows (46.8% and 76.6%, P < 0.05) than in animals at risk (39.4% and 27.3%, P > 0.05). Sixty-six animals (27.5%) were seropositive to both N. caninum and B. abortus , and results showed no significant difference (P > 0.05) with respect to geographical district, breed, and age. This is the first report of N. caninum infection among dairy cattle herds in Pakistan.

Timing of parturition events in Yellowstone bison Bison bison: implications for bison conservation and brucellosis transmission risk to cattle

AbstractYellowstone bison Bison bison are chronically infected with brucellosis (caused by the bacterium Brucella abortus), which raises concerns about possible transmission to cattle when they migrate to winter ranges outside the Yellowstone National Park. We monitored bison from April to mid‐June during 2004‐2007 to estimate the timing and location of parturition events that may shed tissues infected by B. abortus. Observed abortions (N = 29) occurred from January through 19 May, while peak calving (80% of births) occurred from 25 April to 26 May, and calving was finished by 5 June. Observed parturition events (N = 115) occurred in the Park and on the Horse Butte peninsula in Montana, USA, where cattle were not present at any time of the year. Allowing bison to occupy public lands outside the Park where cattle are never present (e.g. Horse Butte peninsula) until most bison calving is completed (late May or early June) is not expected to significantly increase the risk of brucellosis transmission from bison to cattle because: 1) bison parturition is essentially completed weeks before cattle occupy nearby ranges, 2) female bison meticulously consume birthing tissues, 3) ultraviolet light and heat degrade B. abortus on tissues, vegetation and soil, 4) scavengers remove fetuses and remaining birth tissues and 5) management maintains separation between bison and cattle on nearby ranges. Allowing bison to occupy public lands outside the Park through their calving season will help conserve bison migratory behaviour and reduce stress on pregnant females and their newborn calves, while still minimizing the risk of brucellosis transmission to cattle.

Slow virus disease: Deciphering conflicting data on the transmissible spongiform encephalopathies (TSE) also called prion diseases

The transmissible spongiform encephalopathies (TSE) that manifest as Creutzfeldt-Jakob disease in humans, as scrapie in sheep and goats, mad cow disease in cattle, or chronic wasting disease in cervids (deer) represent a serious human health crisis and a significant economical problem. Despite much research, the nature of the elusive pathogen directly involved with TSE is currently unresolved. This article reviews current pathogen-cell plasma membrane properties, showing that the primary biochemical marker of the prion disease is used as a receptor by the intracellular bacterium Brucella abortus. Such observation makes plausible the role for the prion in the pathogenesis of TSE, and supports the concept that Spiroplasma, a wall-less bacterium, may be a transmissible agent of TSE. Over the past three decades, we have published convincing evidence that Spiroplasma infection is associated with TSE. The bacterial-prion-receptor concept by other laboratories support a model for TSE wherein a Spiroplasma bacterium can bind to prion receptors (alone or with anchors) on the cell surface lipid raft, allowing entry of the microbe into the cell to initiate infection. The relevance of this new concept is that it offers a new window for future research involving a bacterium in the pathogenesis of TSE. Data from the bacterial-prion-receptor model will aid in the development diagnostic tests and/or treatment protocols for TSE.

The aquaporin gene aqpX of Brucella abortus is induced in hyperosmotic conditions.

An aquaporin gene (aqpX) was previously detected in the pathogenic bacterium Brucella abortus. Earlier studies showed that AqpX mediated rapid and large water fluxes in both directions in response to sudden osmotic up- or downshifts. Here, to study the role and the expression of the aqpX gene in B. abortus, an aqpX null mutant was constructed using an aqpX : : lacZ gene fusion. This mutant showed no significant difference in growth rate compared to the wild-type strain when grown in rich and minimal media, demonstrating that disruption of the aqpX gene was not lethal for B. abortus. The role of the B. abortus AqpX water channel was investigated by exposing the cells to hypo- and hyperosmolar conditions. While in hyperosmolar environments the growth rate of the knockout mutant was not affected, in hypo-osmolar conditions this mutant showed reduced viability after 50 h of growth. beta-Galactosidase assays and RT-PCR revealed that aqpX gene expression and the amount of aqpX mRNA were markedly increased in hyperosmolar conditions. Moreover, B. abortus aqpX expression levels were enhanced during the mid-exponential phase of growth. These results indicated that the expression of aqpX was regulated during the growth curve and induced in hyperosmolar conditions. This report is believed to be the first example of the induction of a bacterial aquaporin in hypertonic conditions.

A functional water channel protein in the pathogenic bacterium Brucella abortus.

The gene for a new bacterial aquaporin, AqpX, was cloned from the pathogenic Gram-negative bacterium Brucella abortus. The gene was mapped on the large chromosome of B. abortus. It is flanked by one upstream and two downstream copies of the Brucella repeated sequence Bru-RS. Prediction from the nucleotide sequence indicated that the protein is a member of the MIP family, which comprises channels for water and/or solute transport. Expression in Xenopus oocytes and cryoelectron microscopy of Escherichia coli cells transformed with the aqpX gene confirmed that the protein is an efficient water channel. Glycerol uptake experiments in E. coli also showed that the protein is not able to transport glycerol.

Greater Yellowstone's Bison: Unraveling of an Early American Wildlife Conservation Achievement

The Greater Yellowstone region's bison-brucellosis controversy has triggered troublesome proposals giving federal and state agriculture agencies jurisdiction over wildlife to eradicate a domestic livestock disease. Many of the region's bison (Bos bison) and elk (Cervus elaphus) carry the bacterium Brucella abortus, which can cause brucellosis. Local livestock officials fear bison and elk could transmit brucellosis to domestic livestock. jeopardizing state brucellosis class-free status. However, no cases of such transmission in an open range setting have been verified scientifically. Various federal and state agencies have jurisdiction over the region's wildlife and livestock; these agencies are having real difficulty reaching consensus on how to address brucellosis in the wildlife populations. Montana and Idaho recently vested state livestock officials with jurisdiction over bison leaving Yellowstone National Park (YNP), and the U.S. Department of Agriculture's Animal, Plant, and Health Inspection Service (APHIS) has indicated it may propose regulations asserting jurisdiction over bison. An interim bison management plan, the result of a recent court settlement, provides for the National Park Service (NPS) to participate in capturing, testing, and slaughtering Yellowstone's bison, but makes no provision for addressing brucellosis in elk. The region's brucellosis problem could be adequately addressed through a risk management disease control policy rather than a costly and perhaps fruitless eradication effort. Such an approach can be implemented without the unwelcome precedent of livestock officials taking jurisdiction over wildlife.

Lack of Fc epsilon RII expression by murine B cells after in vivo immunization is directly associated with Ig secretion and not Ig isotype switching.

The "low affinity" Fc receptor for IgE (Fc epsilon RII) has been reported to be absent from normal murine and human B cells that express a membrane (m)Ig isotype other than mIgM or mIgD in vivo. This would suggest that Fc epsilon RII expression is specifically lost after in vivo Ig isotype switching. We demonstrate that during a murine immune response to the bacterium Brucella abortus, to goat anti-mouse IgD (G alpha M delta) antibody, or to infection with the nematode parasites Nippostrongylus brasilienis or Heligmosomoides polygyrus, Fc epsilon RII expression is low or absent on virtually all B cells secreting IgM, IgG1, IgG2a, and IgE. However, up to 50% of B cells that express mIgG1 after G alpha M delta injection continue to express Fc epsilon RII. These mIgG1 + Fc epsilon RII+ cells secrete little, if any, IgG1 when placed in vitro, in contrast to their mIgG1 + Fc epsilon RII- counterparts. The mIgG1 + Fc epsilon RII+ cells may be a transitional cell population, because they undergo substantial loss of Fc epsilon RII in culture, unlike mIgM+ Fc epsilon RII+ cells, which maintain constant levels of Fc epsilon RII throughout a comparable culture period. Thus, low or absent expression of Fc epsilon RII after immunization in vivo is directly associated with B cell differentiation to Ig production in the presence or absence of Ig isotype switching. However, all post-switched B cells may eventually lack Fc epsilon RII expression, independently of their differentiative state.

IFN-gamma regulates the isotypes of Ig secreted during in vivo humoral immune responses.

The lymphokine IFN-gamma has been shown in vitro to stimulate IgG2a secretion and inhibit IgG1 and IgE secretion by LPS-activated B lymphocytes. To determine whether IFN-gamma has a similar isotype regulatory role in vivo, we studied the abilities of rIFN-gamma and a mAb to IFN-gamma to modify the isotypes of Ig secreted in mice injected with a goat antibody to mouse IgD, which by itself induces large increases in levels of serum IgG1 and IgE and a relatively small increase in serum IgG2a. Multiple injections of IFN-gamma substantially inhibited production of IgG1 and IgE, and stimulated production of IgG2a in affinity purified goat antibody specific for mouse IgD-treated mice; anti-IFN-gamma antibody blocked the effects of IFN-gamma and in fact enhanced IgG1 and IgE secretion and inhibited the IgG2a response in these mice. The role of IFN-gamma in the selection of isotypes of Ig produced in response to injection of mice with the bacterium Brucella abortus (BA) was also studied, because killed, fixed BA are known to stimulate IFN secretion and a predominantly IgG2a antibody response. Anti-IFN-gamma antibody strongly suppressed IgG2a secretion and stimulated IgG1, but not IgE, secretion in BA-immunized mice. BA suppressed IgG1 and IgE secretion and enhanced IgG2a secretion in affinity purified goat antibody specific for mouse IgD-injected mice; treatment of these mice with anti-IFN-gamma antibody reversed the effects of BA on IgG1 and IgG2a secretion, but not the suppressive effect of BA on IgE secretion. These observations demonstrate that IFN-gamma has an important and perhaps unique physiologic role in the stimulation of IgG2a secretion and in the suppression of secretion of IgG1, whereas bacterial antigens can suppress IgE secretion by other mechanisms in addition to IFN-gamma secretion.

OBSERVATIONS ON THE INFECTION OF CHICK EMBRYOS WITH BACTERIUM TULARENSE, BRUCELLA, AND PASTEURELLA PESTIS

1. Comparison of the infections of chick embryos by the chorio-allantoic route indicates that Bacterium tularense and Brucella suis, abortus, and melitensis exhibit varying degrees of facultative intracellular parasitism. Pasteurella pestis is adapted to rapid proliferation and spread in the intercellular fluids. 2. In the early stages of infection Bacterium tularense has a marked affinity for growth within ectodermal epithelial cells. Brucella suis and Brucella abortus differ in their selectivity for cells of mesodermal derivation and especially in their effect on vascular endothelium. The strain of Brucella melitensis studied is limited in its intracellular growth to ectodermal epithelium. 3. Many of the features characteristic of these infections in the natural hosts are reproduced in the chick embryo and its membranes. 4. The possible implications regarding the differences in behavior of these microorganisms in relation to the problem of infection and pathogenesis of these diseases are discussed.