Brucella: a Mr "Hide" converted into Dr Jekyll

Exposure to Brucella Species, Coxiella burnetii, and Trichinella Species in Recently Imported Camels from Sudan to Egypt: Possible Threats to Animal and Human Health

Brucellosis and coxiellosis/Q fever are bacterial infections caused by Brucella species and Coxiella burnetii, respectively; camels are highly susceptible to both pathogens. Trichinellosis is a parasitic infection caused by various Trichinella nematode species. Reportedly, camels are susceptible to experimental infection with Trichinella spp., but information on this potential host species is scarce. All three infections are of zoonotic nature and thus of great public health concern. The current study aimed to determine antibodies against the three pathogens in recently imported camels (n = 491) from Sudan at the two main ports for the entrance of camels into southern Egypt using commercial indirect ELISAs. Samples were collected in two sampling periods. The seropositivity rates of Brucella spp., C. burnetii, and Trichinella spp. were 3.5%, 4.3%, and 2.4%, respectively. Mixed seropositivity was found in 1% for Brucella spp. and C. burnetii. Marked differences were found between the two study sites and the two sampling periods for Brucella. A higher rate of seropositivity was recorded in the Red Sea/older samples that were collected between 2015 and 2016 (4.3%, 17/391; odds ratio = 9.4; p < 0.030) than in those collected in Aswan/recent samples that were collected between 2018 and 2021 (0/100). Concerning C. burnetii, samples collected during November and December 2015 had a significantly higher positivity rate than the other samples (13%, 13/100; OD = 4.8; p < 0.016). The same effect was observed for antibodies to Trichinella spp., with samples collected during November and December 2015 showing a higher positivity rate than the other samples (7%, 7/100; OD = 10.9; p < 0.001). This study provides valuable information on the seroprevalence of Brucella spp. and additional novel information on C. burnetii and Trichinella spp. in recently imported camels kept in quarantine before delivery to other Egyptian regions. This knowledge can be utilized to reduce health hazards and financial burdens attributable to brucellosis, Q fever, and trichinellosis in animals and humans in Egypt.

Evasion of host defense by Brucella

Brucella , an adept intracellular pathogen, causes brucellosis, a zoonotic disease leading to significant global impacts on animal welfare and the economy. Regrettably, there is currently no approved and effective vaccine for human use. The ability of Brucella to evade host defenses is essential for establishing chronic infection and ensuring stable intracellular growth. Brucella employs various mechanisms to evade and undermine the innate and adaptive immune responses of the host through modulating the activation of pattern recognition receptors (PRRs), inflammatory responses, or the activation of immune cells like dendritic cells (DCs) to inhibit antigen presentation. Moreover, it regulates multiple cellular processes such as apoptosis, pyroptosis, and autophagy to establish persistent infection within host cells. This review summarizes the recently discovered mechanisms employed by Brucella to subvert host immune responses and research progress on vaccines, with the aim of advancing our understanding of brucellosis and facilitating the development of more effective vaccines and therapeutic approaches against Brucella .

Dynamic analysis of sheep Brucellosis model with environmental infection pathways

We develop a mathematical model for the transmission of brucellosis in sheep taking into account external inputs, immunity, stage structure and other factors. We find the the basic reproduction number $ R_0 $ in terms of the model parameters, and prove the global stability of the disease-free equilibrium. Then, the existence and global stability of the endemic equilibrium is proven. Finally, sheep data from Yulin, China are employed to fit the model parameters for three different environmental infection exposure conditions. The variability between different models in terms of control measures are analyzed numerically. Results show that the model is sensitive to the control parameters for different environmental infection exposure functions. This means that in practical modeling, the selection of environmental infection exposure functions needs to be properly considered.

Plasmodium falciparum Nicotinamidase as A Novel Antimalarial Target

Inhibition of Plasmodium falciparum nicotinamidase could represent a potential antimalarial since parasites require nicotinic acid to successfully recycle nicotinamide to NAD⁺, and importantly, humans lack this biosynthetic enzyme. Recently, mechanism-based inhibitors of nicotinamidase have been discovered. The most potent compound inhibits both recombinant P. falciparum nicotinamidase and parasites replication in infected human red blood cells (RBCs). These studies provide evidence for the importance of nicotinamide salvage through nicotinamidase as a central master player of NAD⁺ homeostasis in P. falciparum.

Key immunity characteristics of diverse stages of brucellosis in rural population from Inner Mongolia, China

Background

Brucellosis poses a serious threat to human and animal health, particularly in developing countries such as China. The Inner Mongolia Autonomous Region is one of the most severely brucellosis-endemic provinces in China. Currently, the host immune responses functioning to control Brucella infection and development remain poorly understood. The aim of this study is to further clarify the key immunity characteristics of diverse stages of brucellosis in Inner Mongolia.

Methods

We collected a total of 733 blood samples from acute (n = 137), chronic (n = 316), inapparent (n = 35), recovery (n = 99), and healthy (n = 146) groups from the rural community of Inner Mongolia between 2014 and 2015. The proportions of CD4⁺, CD8⁺, Th1, Th2, and Th17 T cells in peripheral blood and the expression of TLR2 and TLR4 in lymphocytes, monocytes and granulocytes were examined using flow cytometry analysis. The differences among the five groups were compared using one-way ANOVA and the Kruskal–Wallis method, respectively.

Results

Our results revealed that the proportions of CD4⁺ and CD8⁺ T cells were significantly different among the acute, chronic, recovery, and healthy control groups (P < 0.05), with lower proportions of CD4⁺ T cells and a higher proportion of CD8⁺ T cells in the acute, chronic, and recovery groups. The proportion of Th1 cells in the acute, chronic, and inapparent groups was higher than that in the healthy and recovery groups; however, there was no significant difference between patients and healthy individuals (P > 0.05). The proportion of Th2 lymphocytes was significantly higher in the acute and healthy groups than in the inapparent group (P < 0.05). The proportion of Th17 cells in the acute group was significantly higher than that in the healthy control, chronic, and inapparent groups (P < 0.05). Finally, the highest expression of TLR4 in lymphocytes, monocytes and granulocytes was observed in the recovery group, and this was followed by the acute, chronic, healthy control, and inapparent groups. There was a significant difference between the recovery group and the other groups, except for the acute group (P < 0.05). Moreover, a correlation in TLR4 expression was observed in lymphocytes, monocytes and granulocytes among the five groups (r > 0.5), except for the inapparent group between lymphocytes and granulocytes (r = 0.34).

Conclusions

Two key factors (CD8⁺ T cells and TLR4) in human immune profiles may closely correlate with the progression of brucellosis. The detailed function of TLR4 in the context of a greater number of cell types or tissues in human or animal brucellosis and in larger samples should be further explored in the future.

Graphical Abstract

Oral S2-Ag85 DNA Vaccine Activated Intestinal Cell dsDNA and RNA Sensors to Promote the Presentation of Intestinal Antigen

Objective

To explore the molecular mechanism by which oral S2-Ag85DNA vaccines present intestinal antigens. The oral S2-Ag85 vaccine has been shown to protect the human body and effectively improve the titration of the vaccine by acting on intestinal mucosa cells and enhancing their immunogenicity.

Method

Mice were immunized with the recombinant S2-Ag85 vaccine, and antibody secretion was then detected in the intestinal tissue. The molecular mechanisms of in vitro detection sensor molecules RIG-1, Pol III, and related conductor transductor molecules DAI, STING, AIM2, IRF3, and IRF7 were determined by separating intestinal IEC, DC, and IELC cells.

Results

The S2-Ag85A vaccine was effective in activating dsDNA and RNA transduction pathways in intestinal cells and improving intestinal antigen presentation in mice.

Animal and human brucellosis in Algeria: a review

Tawla n Malṭa d aṭṭan ittenṭaḍen ɣer umdan i d-xeddment tbaktiriyin n tewsit Brucella spp. D aṭṭan amaḍlan u tella deg tmura n wagrakal am Lezzayer anda mazal txeddem axessar deg lmal. Ad d-nawi dagi tasɣunt tamatut ɣef tawla n Malṭa di Lezzayer, anda i tt-id-ufan yakan ɣer umdan seg 1895 u deg wass-nni mazal-itt d ugur ameqqran i yimeẓla n tdawsa. Tella tezqaft deg tejṛutin n yimdanen deg temnaḍt ɣer tayeḍ, tamnaḍt yennul ugar d tamnaḍt uzawaɣ i yesɛan weḥd-s aktamur alemmas (tajṛut/100 000 imezdaɣ) n 65.87 teḍfer-itt-id s 9.89 deg temnaḍt Agafa-Asamar ɣef wakken i d-iwekked uɣlif n tdawsa. Aktamur n tejṛutin n tawla n Malṭa n yizgaren iɛedda s uḍfar deg 5% ar 0,76% deg tlemmast n yiseggasen n 90 d 2014 s usileɣ imfeccec anda seld ṣa yiseggasen n wahil n takza d usnefren akked ucraḍ s tgezzayt REV-1 i d-ihegga uɣlif n tdawsa mazal yegguma ad isenger aṭṭan-agi. Ilaq daɣen ad negzu dakken anerni n umḍan n tejṛutin timaynutin n yimdanen i ittujerden kifkif-it akked tejṛutin ɣer tɣeṭṭen i yellan d aɛwin n temsalmit meqqren i umdan di Lezzayer.

Acute brucellosis associated with isolated splenic and left gastric artery vasculitis and acute ischemic bowel infarction. A systematic review of the most recent cases

Brucellosis is a multisystem bacterial zoonosis caused by Gram-negative bacteria Brucella spp. Ingestion of infected food products, direct contact with an infected animal, or inhalation of aerosols are all ways for germs to spread from animals to humans. Intestinal vasculitis with gangrene due to brucellosis has rarely been reported. We report a 62-year-old male patient presenting with acute onset of recurrent attacks of abdominal pain, remittent fever, malaise, and weight loss, which were followed by severe left hypochondrium abdominal pain with rigidity and signs of acute abdomen. Brucellosis was clinically suspected and confirmed by an enzyme-linked immunosorbent assay against the Brucella melitensis species. An abdominal CT scan revealed isolated splenic and left gastric artery vasculitis, leading to acute bowel ischemia, bowel infarction and gangrenous jejunal bowel segment. Histopathological examination of the resected gangrenous bowel segment revealed leucocytoclastic vasculitis. The patient was successfully treated with a standardized antimicrobial therapy for brucellosis and a short course of steroids with a complete resolution of the symptoms and signs. The case is discussed and the literature is reviewed.

Serological and molecular investigation of human brucellosis in participants of Famenin brucellosis cohort study, Hamadan, Iran

Background and Objectives

Brucella is an intracellular pathogen that causes brucellosis in humans and animals. This study aimed to assess the results of brucellosis seroprevalence among participants of the Famenin brucellosis cohort with molecular investigation technique and determine Brucella-approved species.

Materials and Methods

Following the first phase of the Famenin brucellosis cohort in 2016 which investigated the seroprevalence of brucellosis among 2367 participants in Famenin city, a total of 575 people including all seropositive and some seronegative people were examined again by wright serological tests in 2019. The PCR assay was accomplished on all cases that have wright titers ≥ 1/20 for tracing Brucella DNA using BCSP31 target gene and IS711 locus.

Results

Out of 575 studied cases, 145 people had wright titers ≥ 1/20. The PCR reactions of these 145 blood samples were positive in 63/145 (43.44%) tested samples using primers (B4/B5) for Brucella genus detection. In the second PCR assay using specific-primers for Brucella abortus and Brucella melitensis, 18/63 (28.57%) of the samples were diagnosed as B. abortus, and 18/63 (28.57%) were diagnosed as B. melitensis.

Conclusion

In this study, using the selected specific genes for the diagnosis of Brucella in the genus and species levels, the PCR technique was evaluated as a promising method for the rapid and safe detection of brucellosis besides the serological test for more accurate detection of brucellosis especially in cases that are not definitive.

Immunometabolism in human brucellosis: An emerging field of investigation

In recent years, extreme attention has been focused on the role of immunometabolism in the regulation of immune cell responses in healthy individuals during infection, autoimmunity, and cancer. In the infection biology area, it has been shown that there is a close relationship between the immune system and the host metabolic changes. Brucella species is an intracellular coccobacillus that infects humans and mammals, which led to brucellosis. Brucella species with host-specific evolutionary mechanisms allow it to hide from or manipulate cellular immunity and achieve intracellular persistence. Intracellular bacterial pathogens such as Brucella species also employ host cell resources to replicate and persist inside the host. Targeting these host systems is one promising strategy for developing novel antimicrobials to tackle intracellular infections. This study will summarize the role of metabolic reprogramming in immune cells and their relationship to brucellosis.

Pathological changes, distribution and detection of Brucella melitensis in foetuses of experimentally-infected does

Background

Brucellosis of goats is caused by Brucella melitensis. It is a re-emerging zoonotic disease in many countries due to transmission from domestic animals and wildlife such as ibex, deer and wild buffaloes.

Objective

To describe the pathological changes, identification and distribution of B. melitensis in foetuses of experimentally infected does.

Methods

Twelve female goats of approximately 90 days pregnant were divided into 4 groups. Group 1 was exposed intra-conjunctival to 100 µL of sterile PBS while goats of Groups 2, 3 and 4 were similarly exposed to 100 µL of an inoculum containing 10⁹ CFU/mL of live B. melitensis. Goats of these groups were killed at 15, 30 and 60 days post-inoculation, respectively. Foetal fluid and tissues were collected for bacterial identification (using direct bacterial culture, PCR and immuno-peroxidase staining) and histopathological examination.

Results

Bilateral intra-conjunctival exposure of pregnant does resulted in in-utero infection of the foetuses. All full-term foetuses of group 4 were either aborted or stillborn, showing petechiations of the skin or absence of hair coat with subcutaneous oedema. The internal organs showed most severe lesions. Immune-peroxidase staining revealed antigen distribution in all organs that became most extensive in group 4. Brucella melitensis was successfully isolated from the stomach content, foetal fluid and various other organs.

Conclusion

Vertical transmission of caprine brucellosis was evident causing mild to moderate lesions in different organs. The samples of choice for isolation and identification of B. melitensis are stomach content as well as liver and spleen tissue.

Quantification of Brucella abortus population structure in a natural host

Cattle are natural hosts of the intracellular pathogen Brucella abortus, which inflicts a significant burden on the health and reproduction of these important livestock. The primary routes of infection in field settings have been described, but it is not known how the bovine host shapes the structure of B. abortus populations during infection. We utilized a library of uniquely barcoded B. abortus strains to temporally and spatially quantify population structure during colonization of cattle through a natural route of infection. Introducing 10⁸ bacteria from this barcoded library to the conjunctival mucosa resulted in expected levels of local lymph node colonization at a 1-wk time point. We leveraged variance in strain abundance in the library to demonstrate that only 1 in 10,000 brucellae introduced at the site of infection reached a parotid lymph node. Thus, cattle restrict the overwhelming majority of B. abortus introduced via the ocular conjunctiva at this dose. Individual strains were spatially restricted within the host tissue, and the total B. abortus census was dominated by a small number of distinct strains in each lymph node. These results define a bottleneck that B. abortus must traverse to colonize local lymph nodes from the conjunctival mucosa. The data further support a model in which a small number of spatially isolated granulomas founded by unique strains are present at 1 wk postinfection. These experiments demonstrate the power of barcoded transposon tools to quantify infection bottlenecks and to define pathogen population structure in host tissues.

The Not-So-Strange Case of Dr. Jekyll and Mr. Hyde in Antibiotic Research: An Interdisciplinary Opportunity

Literary-rhetorical devices like figurative language and analogy can help explain concepts that exceed our capacity to grasp intuitively. It is not surprising these devices are used to discuss virulence, pathogenesis, and antibiotics. Allusions to Robert Louis Stevenson’s Strange Case of Dr. Jekyll and Mr. Hyde seem to be used with particular frequency in research pertaining to pathogens, especially in studies contemporary with our evolving understanding of antibiotic resistance. More recent references to the text have appeared in research parsing definitions of virulence and acknowledging the role of anti-virulence in future therapeutics. While it is obvious that scientists invoke Stevenson’s story for stylistic purposes, its use could go beyond the stylistic—and might even generate rhetorical and imaginative possibilities for framing research. This perspective discusses the first published allusion to Jekyll and Hyde in reference to virulence and pathogenesis; comments on a select number of specific instances of Jekyll and Hyde in contemporary scientific literature; briefly contextualizes the novel; and concludes with the implications of a more productive engagement with humanistic disciplines in the face of antibiotic resistance.

Genomic insights into Brucella

Brucellosis is a zoonotic disease caused by certain species of Brucella. Each species has its preferred host animal, though it can infect other animals too. For a longer period, only six classical species were recognized in the genus Brucella. No vaccine is available for human brucellosis. Therefore, human brucellosis can be controlled only by controlling brucellosis in animals. The genus is now expanding with the newly isolated atypical strains from various animals, including marine mammals. Presently, 12 species of Brucella have been recognized. The first genome of Brucella was released in 2002, and today, we have more than 1500 genomes of Brucella spp. isolated worldwide. Multiple genome sequences are available for the major zoonotic species, B. abortus, B. melitensis, and B. suis. The Brucella genome has two chromosomes with the approximate sizes of 2.1 and 1.2 Mbp. The genome of Brucella is highly conserved across all the species at the nucleotide level. One of the unanswered questions is what makes host preference in different species of Brucella. Here, I summarize the recent advancements in the Brucella genomics research.

Direct correlation between Th1 and Th17 responses in immunity to Brucella infection

Th1 cells play a central role in immunity to brucellosis, while the exact role of Th17 cells has remained unknown. This study aimed to evaluate the peripheral distributions of Th1 and Th17 cells and serum levels of IFN-γ, IL-17A and IL-22 cytokines in brucellosis patients. One hundred patients (36 acute, 41 under-treatment and 23 relapsed) and 30 age- and sex-matched healthy controls were included. The frequencies of Th1 and Th17 cells were determined by flow cytometric analysis. Serum levels of IFN-γ, IL-17A and IL-22 were measured by multi-analyte flow assay. Increased frequencies of Th1 and Th17 cells were observed in acute and relapsed brucellosis versus under-treatment patients and healthy controls (P < 0.05). The mean serum levels of IFN-γ were significantly elevated in acute and relapsed groups compared to under-treatment patients (P = 0.002 and P = 0.01 respectively). Acute patients showed higher levels of IL-22 than under-treatment (P = 0.008). Direct correlations were found between increased frequencies of Th1 and Th17 cells in acute and relapsed patients (P = 0.007 and P = 0.001 respectively) and between IL-17A and IL-22 in both groups of patients. Our findings indicate a cooperative role for Th1 and Th17 cells in immunity to brucellosis which is more evident during acute and relapse phases of brucellosis.

A high-throughput screening for inhibitors of riboflavin synthase identifies novel antimicrobial compounds to treat brucellosis

Brucella spp. are pathogenic intracellular Gram-negative bacteria adapted to life within cells of several mammals, including humans. These bacteria are the causative agent of brucellosis, one of the zoonotic infections with the highest incidence in the world and for which a human vaccine is still unavailable. Current therapeutic treatments against brucellosis are based on the combination of two or more antibiotics for prolonged periods, which may lead to antibiotic resistance in the population. Riboflavin (vitamin B2) is biosynthesized by microorganisms and plants but mammals, including humans, must obtain it from dietary sources. Owing to the absence of the riboflavin biosynthetic enzymes in animals, this pathway is nowadays regarded as a rich resource of targets for the development of new antimicrobial agents. In this work, we describe a high-throughput screening approach to identify inhibitors of the enzymatic activity of riboflavin synthase, the last enzyme in this pathway. We also provide evidence for their subsequent validation as potential drug candidates in an in vitro brucellosis infection model. From an initial set of 44 000 highly diverse low molecular weight compounds with drug-like properties, we were able to identify ten molecules with 50% inhibitory concentrations in the low micromolar range. Further Brucella culture and intramacrophagic replication experiments showed that the most effective bactericidal compounds share a 2-Phenylamidazo[2,1-b][1,3]benzothiazole chemical scaffold. Altogether, these findings set up the basis for the subsequent lead optimization process and represent a promising advancement in the pursuit of novel and effective antimicrobial compounds against brucellosis.

Periplasmic protein EipA determines envelope stress resistance and virulence in Brucella abortus

Molecular components of the Brucella abortus cell envelope play a major role in its ability to infect, colonize and survive inside mammalian host cells. In this study, we have defined a role for a conserved gene of unknown function in B. abortus envelope stress resistance and infection. Expression of this gene, which we name eipA, is directly activated by the essential cell cycle regulator, CtrA. eipA encodes a soluble periplasmic protein that adopts an unusual eight-stranded β-barrel fold. Deletion of eipA attenuates replication and survival in macrophage and mouse infection models, and results in sensitivity to treatments that compromise the cell envelope integrity. Transposon disruption of genes required for LPS O-polysaccharide biosynthesis is synthetically lethal with eipA deletion. This genetic connection between O-polysaccharide and eipA is corroborated by our discovery that eipA is essential in Brucella ovis, a naturally rough species that harbors mutations in several genes required for O-polysaccharide production. Conditional depletion of eipA expression in B. ovis results in a cell chaining phenotype, providing evidence that eipA directly or indirectly influences cell division in Brucella. We conclude that EipA is a molecular determinant of Brucella virulence that functions to maintain cell envelope integrity and influences cell division.

Lable-free based comparative proteomic analysis of secretory proteins of rough Brucella mutants

Brucella rough mutants are reported to induce infected macrophage death, which is type IV secretion system (T4SS) dependent. T4SS and its secretory proteins play a major role in host-bacteria interactions, but the crucial secretory proteins to promote macrophage death during Brucella rough mutant infection have not been characterized. In this study, we found that T4SS components played no role for macrophage death induced by Brucella rough mutant infection, but some T4SS effectors did. Proteomics of secretory proteins from Brucella rough mutants ΔrfbE and ΔrfbEΔvirB123 was analyzed by liquid chromatography/tandem mass spectrometry and 861 unique proteins were identified, among which 37 were differential secretory proteins. Gene ontology and pathway analysis showed that differential secretory proteins involved in cellular process and metabolic process, distributed in the cell and membrane, possessed molecular function of catalytic activity and binding, and were associated with ribosome, NOD-like receptor signaling pathway, two-component system and bacterial secretion system. Cell death analysis showed that T4SS effector VceC, and two differential secretory proteins OmpW family protein (BAB1_1579) and protein BAB1_1185 were associated with Brucella cytotoxicity. This study provides new insights into the molecular mechanisms associated with Brucella cytotoxicity and valuable information for screening vaccine candidates for Brucella. SIGNIFICANCE: Brucella rough mutants induce infected macrophage death, which is T4SS dependent. In the present report, a comparative proteomics analysis revealed 37 differential secretory proteins between Brucella rough mutants ΔrfbE and ΔrfbEΔvirB123. Further study demonstrated OmpW family protein (BAB1_1579) and uncharacterized protein BAB1_1185, two differential secretory proteins, were associated with Brucella cytotoxicity. This study provides novel information of the secretory proteins from the Brucella rough mutants and their effects on the Brucella cytotoxicity.

Pathological changes and bacteriological assessments in the urinary tract of pregnant goats experimentally infected with Brucella melitensis

Background

This study was conducted to investigate the pathological changes and distribution of B. melitensis in the urinary tract of pregnant goats following acute experimental infection. Six Jamnapari crossbred does in their third trimester of pregnancy were randomly assigned into two groups; Group 1 was uninfected control and Group 2 was inoculated conjunctival with 0.1 mL of the inoculums containing 10⁹ cfu/mL of live B. melitensis. All does were sacrificed 30 days post-inoculation before the kidney, ureter, urinary bladder, urethra and vaginal swab were collected for isolation of B. melitensis. The same tissue samples were fixed in 10% neutral buffered formalin for hematoxylin and eosin, and immunoperoxidase staining.

Results

None of the goats showed clinical signs or gross lesions. The most consistent histopathology finding was the infiltration of mononuclear cells, chiefly the macrophages with few lymphocytes and occasionally neutrophils in all organs along the urinary tract of the infected goats of Group 2. Other histopathology findings included mild necrosis of the epithelial cells of the renal tubules, congestion and occasional haemorrhages in the various tissues. Kidneys showed the most severe lesions. Immunoperoxidase staining revealed the presence of B. melitensis within the infiltrating macrophages and the epithelium of renal tubules, ureter, urethra and urinary bladder. Most extensive distribution was observed in the urinary bladder. Brucella melitensis was successfully isolated at low concentration (3.4 × 10³ cfu/g) in the various organs of the urinary tract and at high concentration (2.4 × 10⁸ cfu/mL) in the vaginal swabs of all infected goats. Although B. melitensis was successfully isolated from the various organs of the urinary tract, it was not isolated from the urine samples that were collected from the urinary bladder at necropsy.

Conclusion

This study demonstrates the presence of low concentrations of B. melitensis in the organs of urinary tract of pregnant does, resulting in mild histopathology lesions. However, B. melitensis was not isolated from the urine that was collected from the urinary bladder.

Toll-Like Receptors 2 and 4 Cooperate in the Control of the Emerging Pathogen Brucella microti

Toll-like receptors (TLRs) recognize pathogen-derived molecules and play a critical role during the host innate and adaptive immune response. Brucella spp. are intracellular gram-negative bacteria including several virulent species, which cause a chronic zoonotic infection in a wide range of mammalian hosts known as brucellosis. A new Brucella species, Brucella microti, was recently isolated from wild rodents and found to be highly pathogenic in mice. Using this species-specific model, it was previously found that CD8⁺ T cells are required to control this infection. In order to find out the role of TLR-mediated responses in the control of this pathogen, the course of infection of B. microti was analyzed over 3 weeks in wild-type (WT) and TLR knock out (KO) mice including TLR2^-/-, TLR4^-/-, TLR9^-/-, TLR2×4^-/- and TLR2×4×9^-/-. WT and single TLR2, TLR4 and TLR9 KO mice similarly control infection in liver and spleen. In contrast, bacterial clearance was delayed in TLR2×4^-/- and TLR2×4×9^-/- mice at 7 and 14 days post-infection. This defect correlated with impaired maturation and pro-inflammatory cytokine production in B. microti-infected dendritic cells from TLR2×4^-/- and TLR2×4×9^-/- mice. Finally, it was found that Tc cells from TLR2×4^-/- and TLR2×4×9^-/- mice showed reduced ability to inhibit growth of B. microti in macrophages, suggesting the involvement of TLR2 and 4 in the generation of specific Tc cells. Our findings indicate that TLR2 and TLR4 are required to control B. microti infection in mice and that this effect could be related to its participation in the maturation of dendritic cells and the generation of specific CD8⁺ Tc cells.

Modelling Seasonal Brucellosis Epidemics in Bayingolin Mongol Autonomous Prefecture of Xinjiang, China, 2010-2014

Brucellosis is one of the severe public health problems; the cumulative number of new human brucellosis cases reached 211515 from 2010 to 2014 in China. Bayingolin Mongol Autonomous Prefecture is situated in the southeast of Xinjiang, where brucellosis infection occurs every year. Based on the reported data of newly acute human brucellosis cases for each season in Bayingolin Mongol Autonomous Prefecture, we proposed a susceptible, exposed, infected, and vaccinated (SEIV) model with periodic transmission rates to investigate the seasonal brucellosis transmission dynamics among sheep/cattle and from sheep/cattle to humans. Compared with the criteria of MAPE and RMSPE, the model simulations agree to the data on newly acute human brucellosis. We predict that the number of newly acute human brucellosis is increasing and will peak 15325 [95% CI: 11920-18242] around the summer of 2023. We also estimate the basic reproduction number R₀ = 2.5524 [95% CI: 2.5129-2.6225] and perform some sensitivity analysis of the newly acute human brucellosis cases and the basic reproduction number R₀ in terms of model parameters. Our study demonstrates that reducing the birth number of sheep/cattle, raising the slaughter rate of infected sheep/cattle, increasing the vaccination rate of susceptible sheep/cattle, and decreasing the loss rate of vaccination are effective strategies to control brucellosis epidemic.

Establishment of Chronic Infection: Brucella's Stealth Strategy

Brucella is a facultative intracellular pathogen that causes zoonotic infection known as brucellosis which results in abortion and infertility in natural host. Humans, especially in low income countries, can acquire infection by direct contact with infected animal or by consumption of animal products and show high morbidity, severe economic losses and public health problems. However for survival, host cells develop complex immune mechanisms to defeat and battle against attacking pathogens and maintain a balance between host resistance and Brucella virulence. On the other hand as a successful intracellular pathogen, Brucella has evolved multiple strategies to evade immune response mechanisms to establish persistent infection and replication within host. In this review, we mainly summarize the "Stealth" strategies employed by Brucella to modulate innate and the adaptive immune systems, autophagy, apoptosis and possible role of small noncoding RNA in the establishment of chronic infection. The purpose of this review is to give an overview for recent understanding how this pathogen evades immune response mechanisms of host, which will facilitate to understanding the pathogenesis of brucellosis and the development of novel, more effective therapeutic approaches to treat brucellosis.

Computational prediction of secretion systems and secretomes of Brucella: identification of novel type IV effectors and their interaction with the host

Brucella spp. are facultative intracellular pathogens that cause brucellosis in various mammals including humans. Brucella survive inside the host cells by forming vacuoles and subverting host defence systems. This study was aimed to predict the secretion systems and the secretomes of Brucella spp. from 39 complete genome sequences available in the databases. Furthermore, an attempt was made to identify the type IV secretion effectors and their interactions with host proteins. We predicted the secretion systems of Brucella by the KEGG pathway and SecReT4. Brucella secretomes and type IV effectors (T4SEs) were predicted through genome-wide screening using JVirGel and S4TE, respectively. Protein-protein interactions of Brucella T4SEs with their hosts were analyzed by HPIDB 2.0. Genes coding for Sec and Tat pathways of secretion and type I (T1SS), type IV (T4SS) and type V (T5SS) secretion systems were identified and they are conserved in all the species of Brucella. In addition to the well-known VirB operon coding for the type IV secretion system (T4SS), we have identified the presence of additional genes showing homology with T4SS of other organisms. On the whole, 10.26 to 14.94% of total proteomes were found to be either secreted (secretome) or membrane associated (membrane proteome). Approximately, 1.7 to 3.0% of total proteomes were identified as type IV secretion effectors (T4SEs). Prediction of protein-protein interactions showed 29 and 36 host-pathogen specific interactions between Bos taurus (cattle)-B. abortus and Ovis aries (sheep)-B. melitensis, respectively. Functional characterization of the predicted T4SEs and their interactions with their respective hosts may reveal the secrets of host specificity of Brucella.

Genotyping of human Brucella melitensis biovar 3 isolated from Shanxi Province in China by MLVA16 and HOOF

Background

Brucellosis presents a significant economic burden for China because it causes reproductive failure in host species and chronic health problems in humans. These problems can involve multiple organs. Brucellosis is highly endemic in Shanxi Province China. Molecular typing would be very useful to epidemiological surveillance. The purpose of this study was to assess the diversity of Brucella melitensis strains for epidemiological surveillance. Historical monitoring data suggest that Brucella melitensis biovar 3 is the predominant strain associated with the epidemic of brucellosis in Shanxi Province.

Methods/Principal Findings

Multiple-locus variable-number repeat analysis (MLVA-16) and hypervariable octameric oligonucleotide fingerprinting (HOOF-print) were used to type a human-hosted Brucella melitensis population (81 strains). Sixty-two MLVA genotypes (discriminatory index: 0.99) were detected, and they had a genetic similarity coefficient ranging from 84.9% to 100%. Eighty strains of the population belonged to the eastern Mediterranean group with panel 1 genotypes 42 (79 strains) and 43 (1 strain). A new panel 1 genotype was found in this study. It was named 114 MLVAorsay genotype and it showed similarity to the two isolates from Guangdong in a previous study. Brucella melitensis is distributed throughout Shanxi Province, and like samples from Inner Mongolia, the eastern Mediterranean genotype 42 was the main epidemic strain (97%). The HOOF-printing showed a higher diversity than MLVA-16 with a genetic similarity coefficient ranging from 56.8% to 100%.

Conclusions

According to the MLVA-16 and HOOF-printing results, both methods could be used for the epidemiological surveillance of brucellosis. A new genotype was found in both Shanxi and Guangdong Provinces. In areas with brucellosis, the MLVA-16 scheme is very important for tracing cases back to their origins during outbreak investigations. It may facilitate the expansion and eradication of the disease.

Effects of climate change on the persistence and dispersal of foodborne bacterial pathogens in the outdoor environment: A review

According to the Intergovernmental Panel on Climate Change (IPCC), warming of the climate system is unequivocal. Over the coming century, warming trends such as increased duration and frequency of heat waves and hot extremes are expected in some areas, as well as increased intensity of some storm systems. Climate-induced trends will impact the persistence and dispersal of foodborne pathogens in myriad ways, especially for environmentally ubiquitous and/or zoonotic microorganisms. Animal hosts of foodborne pathogens are also expected to be impacted by climate change through the introduction of increased physiological stress and, in some cases, altered geographic ranges and seasonality. This review article examines the effects of climatic factors, such as temperature, rainfall, drought and wind, on the environmental dispersal and persistence of bacterial foodborne pathogens, namely, Bacillus cereus, Brucella, Campylobacter, Clostridium, Escherichia coli, Listeria monocytogenes, Salmonella, Staphylococcus aureus, Vibrio and Yersinia enterocolitica. These relationships are then used to predict how future climatic changes will impact the activity of these microorganisms in the outdoor environment and associated food safety issues. The development of predictive models that quantify these complex relationships will also be discussed, as well as the potential impacts of climate change on transmission of foodborne disease from animal hosts.

Potential risk of blood transfusion-transmitted brucellosis in an endemic area of China

BACKGROUND

Brucellosis is a severe zoonotic disease that is increasingly prevalent in north China. A study evaluating Brucella infection in blood donors was conducted at Kashi central blood station, Xinjiang, China.

STUDY DESIGN AND METHODS

Four serologic and two molecular methods of detection of Brucella infection were used in plasma samples from blood donations collected from Kashi in northwest China, considered a brucellosis-endemic area. Blood donor samples collected in Shenzhen, southern China, a brucellosis-nonendemic area, were tested as a negative control group.

RESULTS

In 3896 plasma samples collected from Kashi central blood station, 135 (3.5%) plasma samples were reactive by the Rose Bengal plate test (RBPT), and 120 (3.1%) of the 135 RBPT-reactive sample were also reactive with the standard tube agglutination test (SAT), respectively. All samples of the control group of 399 blood samples from Shenzhen blood center tested negative with RBPT and SAT. Of 135 seroreactive plasma samples, 39 (1.0%) reacted with B. melitensis membrane protein extracts by enzyme-linked immunosorbent assay and 25 were reactive to either rBP26 or rOMP31 by Western blot. Thirteen plasma samples and two follow-up blood samples were identified as carrying Brucella DNA by quantitative polymerase chain reaction (PCR) and nested PCR. Overall 15 (1:300) Kashi blood donations were found positive by nucleic acid testing, confirmed specific by DNA sequencing.

CONCLUSIONS

The data indicate a probable high rate of Brucella bacteremia, suggesting a potential risk of transfusion-transmitted brucellosis. Blood donation screening for Brucella infection may be considered in the high Brucella-endemic areas of China.

Use of S-[2,3-bispalmitoyiloxy-(2R)-propyl]-R-cysteinyl-amido-monomethoxy polyethylene glycol as an adjuvant improved protective immunity associated with a DNA vaccine encoding Cu,Zn superoxide dismutase of Brucella abortus in mice

This study was conducted to evaluate the immunogenicity and protective efficacy of a DNA vaccine encoding Brucella abortus Cu,Zn superoxide dismutase (SOD) using the Toll-like receptor 2/6 agonist S-[2,3-bispalmitoyiloxy-(2R)-propyl]-R-cysteinyl-amido-monomethoxy polyethylene glycol (BPPcysMPEG) as an adjuvant. Intranasal coadministration of BPPcysMPEG with a plasmid carrying the SOD-encoding gene (pcDNA-SOD) into BALB/c mice elicited antigen-specific humoral and cellular immune responses. Humoral responses were characterized by the stimulation of IgG2a and IgG1 and by the presence of SOD-specific secretory IgA in nasal and bronchoalveolar lavage fluids. Furthermore, T-cell proliferative responses and increased production of gamma interferon were also observed upon splenocyte restimulation with recombinant SOD. Cytotoxic responses were also stimulated, as demonstrated by the lysis of RB51-SOD-infected J774.A1 macrophages by cells recovered from immunized mice. The pcDNA-SOD/BPPcysMPEG formulation induced improved protection against challenge with the virulent strain B. abortus 2308 in BALB/c mice over that provided by pcDNA-SOD, suggesting the potential of this vaccination strategy against Brucella infection.

Increasing threat of brucellosis to low-risk persons in urban settings, China

Cases of brucellosis were diagnosed in 3-month-old twins and their mother. An epidemiologic survey suggested that raw sheep or goat meat might be the source of Brucella melitensis infection. This finding implies that the increasing threat of brucellosis might affect low-risk persons in urban settings in China.

A translocated effector required for Bartonella dissemination from derma to blood safeguards migratory host cells from damage by co-translocated effectors

Numerous bacterial pathogens secrete multiple effectors to modulate host cellular functions. These effectors may interfere with each other to efficiently control the infection process. Bartonellae are Gram-negative, facultative intracellular bacteria using a VirB type IV secretion system to translocate a cocktail of Bartonellaeffector proteins (Beps) into host cells. Based on in vitro infection models we demonstrate here that BepE protects infected migratory cells from injurious effects triggered by BepC and is required for in vivo dissemination of bacteria from the dermal site of inoculation to blood. Human endothelial cells (HUVECs) infected with a ΔbepE mutant of B. henselae (Bhe) displayed a cell fragmentation phenotype resulting from Bep-dependent disturbance of rear edge detachment during migration. A ΔbepCE mutant did not show cell fragmentation, indicating that BepC is critical for triggering this deleterious phenotype. Complementation of ΔbepE with BepE_Bhe or its homologues from other Bartonella species abolished cell fragmentation. This cyto-protective activity is confined to the C-terminal Bartonellaintracellular delivery (BID) domain of BepE_Bhe (BID2.E_Bhe). Ectopic expression of BID2.E_Bhe impeded the disruption of actin stress fibers by Rho Inhibitor 1, indicating that BepE restores normal cell migration via the RhoA signaling pathway, a major regulator of rear edge retraction. An intradermal (i.d.) model for B. tribocorum (Btr) infection in the rat reservoir host mimicking the natural route of infection by blood sucking arthropods allowed demonstrating a vital role for BepE in bacterial dissemination from derma to blood. While the Btr mutant ΔbepDE was abacteremic following i.d. inoculation, complementation with BepE_Btr, BepE_Bhe or BIDs.E_Bhe restored bacteremia. Given that we observed a similar protective effect of BepE_Bhe on infected bone marrow-derived dendritic cells migrating through a monolayer of lymphatic endothelial cells we propose that infected dermal dendritic cells may be involved in disseminating Bartonella towards the blood stream in a BepE-dependent manner.

Cell migration, a fundamental feature of eukaryotic cells, plays a crucial role in mounting an effective immune response. However, several pathogens subvert the migratory properties of infected host cells to their benefit, such as using them as Trojan horses to disseminate within the host. Bartonella effector proteins (Beps) are bona fide virulence factors indispensable for the colonization of mammalian target cells. However, their multiple interferences with host cellular signaling processes might culminate in deleterious secondary effects that require additional effectors to maintain the host cell integrity. A striking example is BepE, which is shown here to preserve endothelial cells (ECs) from fragmentation and to inhibit the defects of dendritic cell (DCs) migration caused by BepC and possibly other Beps. Moreover, BepE is essential for Bartonella dissemination from the dermal site of inoculation to the blood stream where bacteria establish long-lasting intraerythrocytic bacteremia as a hallmark of infection in the mammalian reservoir host. Migration of Bartonella-infected DCs through a monolayer of lymphatic ECs was also found to be dependent of BepE, suggesting that BepE is required to preserve the migratory capability of DCs, a candidate cell type for systemic dissemination from the dermal site of inoculation.

Brucella arteritis: clinical manifestations, treatment, and prognosis

Brucellosis is the most common bacterial zoonosis, and causes a considerable burden of disease in endemic countries. Cardiovascular involvement is the main cause of mortality due to infection with Brucella spp, and most commonly manifests as endocarditis, peripheral and cerebrovascular aneurysms, or arterial and venous thromboses. We report a case of brucellosis presenting as bacteraemia and aortic endarteritis 18 years after the last known exposure to risk factors for brucella infection. The patient was treated with doxycycline, rifampicin, and gentamicin, and underwent surgical repair of a penetrating aortic ulcer, with a good clinical recovery. We review the signs and symptoms, diagnostic approach, prognosis, and treatment of brucella arteritis. We draw attention to the absence of consensus about the optimum therapy for vascular brucellosis, and the urgent need for additional studies and renewed scientific interest in this major pathogen.

Crystallographic and kinetic study of riboflavin synthase from Brucella abortus, a chemotherapeutic target with an enhanced intrinsic flexibility

Riboflavin synthase (RS) catalyzes the last step of riboflavin biosynthesis in microorganisms and plants, which corresponds to the dismutation of two molecules of 6,7-dimethyl-8-ribityllumazine to yield one molecule of riboflavin and one molecule of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. Owing to the absence of this enzyme in animals and the fact that most pathogenic bacteria show a strict dependence on riboflavin biosynthesis, RS has been proposed as a potential target for antimicrobial drug development. Eubacterial, fungal and plant RSs assemble as homotrimers lacking C3 symmetry. Each monomer can bind two substrate molecules, yet there is only one active site for the whole enzyme, which is located at the interface between two neighbouring chains. This work reports the crystallographic structure of RS from the pathogenic bacterium Brucella abortus (the aetiological agent of the disease brucellosis) in its apo form, in complex with riboflavin and in complex with two different product analogues, being the first time that the structure of an intact RS trimer with bound ligands has been solved. These crystal models support the hypothesis of enhanced flexibility in the particle and also highlight the role of the ligands in assembling the unique active site. Kinetic and binding studies were also performed to complement these findings. The structural and biochemical information generated may be useful for the rational design of novel RS inhibitors with antimicrobial activity.

Brucella evasion of adaptive immunity

The complex immune system of mammals is the result of evolutionary forces that include battles against pathogens, as sensing and defeating intruders is a prerequisite to host survival. On the other hand, microorganisms have evolved multiple mechanisms to evade both arms of immunity: the innate and the adaptive immune systems. The successful pathogenic intracellular bacterium Brucella is not an exception to the rule: Brucella displays mechanisms that allow evasion of immune surveillance in order to establish persistent infections in mammals. In this review, we highlight some key mechanisms that pathogenic Brucella use to evade the adaptive immune system.

BtaE, an adhesin that belongs to the trimeric autotransporter family, is required for full virulence and defines a specific adhesive pole of Brucella suis

Brucella is responsible for brucellosis, one of the most common zoonoses worldwide that causes important economic losses in several countries. Increasing evidence indicates that adhesion of Brucella spp. to host cells is an important step to establish infection. We have previously shown that the BmaC unipolar monomeric autotransporter mediates the binding of Brucella suis to host cells through cell-associated fibronectin. Our genome analysis shows that the B. suis genome encodes several additional potential adhesins. In this work, we characterized a predicted trimeric autotransporter that we named BtaE. By expressing btaE in a nonadherent Escherichia coli strain and by phenotypic characterization of a B. suis ΔbtaE mutant, we showed that BtaE is involved in the binding of B. suis to hyaluronic acid. The B. suis ΔbtaE mutant exhibited a reduction in the adhesion to HeLa and A549 epithelial cells compared with the wild-type strain, and it was outcompeted by the wild-type strain in the binding to HeLa cells. The knockout btaE mutant showed an attenuated phenotype in the mouse model, indicating that BtaE is required for full virulence. BtaE was immunodetected on the bacterial surface at one cell pole. Using old and new pole markers, we observed that both the BmaC and BtaE adhesins are consistently associated with the new cell pole, suggesting that, in Brucella, the new pole is functionally differentiated for adhesion. This is consistent with the inherent polarization of this bacterium, and its role in the invasion process.

Yersinia enterocolitica serotype O:9 cultured from Swedish sheep showing serologically false-positive reactions for Brucella melitensis

In a herd of 20 sheep in Sweden, a country where brucellosis has never been diagnosed in sheep or goats, a total of six sheep were found serologically positive to Brucella melitensis in two different rounds of sampling. Yersinia enterocolitica serotype O:9 could at the time of the second sampling be isolated from four sheep, one of them at the same time serologically positive for B. melitensis. The article describes the case and gives some background information on brucellosis and Y. enterocolitica in general as well as a more specific description of the Swedish surveillance program for B. melitensis and the test procedures used. The problem with false-positive reactions, in particular its implications for surveillance programs in low prevalence or officially brucellosis-free countries, is discussed.

A rare case of seronegative culture--proven infection with Brucella suis

Brucellosis is a chronic infection produced by members of the Brucella family. Diagnosis of this condition requires either isolation of the organism in culture or positive serological tests.We describe a 27-year-old male admitted as a case of pyrexia of unknown origin (PUO), who tested negative for Brucella IgM ELISA test on preliminary evaluation but was subsequently diagnosed on the strength of positive blood and bone marrow cultures to be a case of brucellosis secondary to Brucella suis infection. In addition to highlighting the pathogenic potential of an unusual organism, this case demonstrates the unreliability of standard serological tests based on the Brucella melitensis antigen for infection with other species of Brucella.

Acellular vaccines for ovine brucellosis: a safer alternative against a worldwide disease

Ovine brucellosis is a very contagious zoonotic disease distributed worldwide and constitutes a very important zoosanitary and economic problem. The control of the disease includes animal vaccination and slaughter of infected flocks. However, the commercially available vaccine in most countries is based on the attenuated strain Brucella melitensis Rev 1, which presents important safety drawbacks. This review is focused on the most recent and promising acellular vaccine proposals.

Brucellosis in Turkey -- an overview

Although almost a century has gone by since its first description in the country, Turkey has not been able to eradicate brucellosis, which remains a major public health problem. In this review, we give an overview of the epidemiological and epizootic status of brucellosis in Turkey. Although little readily accessible data concerning the epidemiology of brucellosis in Turkey are available, the limited official and published data were analyzed. Despite being endemic in Turkey, brucellosis remains under-diagnosed and under-reported. Adherence to traditional farming practices and lifestyles and the consumption of fresh dairy produce contribute to the high incidence of brucellosis. The successful implementation of a national brucellosis control program requires strong political will, good funding, and collaboration, especially between the public health and veterinary sectors. Primary healthcare workers should always keep the symptoms of acute and chronic brucellosis in mind when treating patients.

Oral immunization of mice with recombinant Lactococcus lactis expressing Cu,Zn superoxide dismutase of Brucella abortus triggers protective immunity

Brucella infections mainly occur through mucosal surfaces. Thus, the development of mucosal administered vaccines could be instrumental for the control of brucellosis. Here, we evaluated the usefulness of recombinant Lactococcus lactis secreting Brucella abortus Cu-Zn superoxide dismutase (SOD) as oral antigen delivery system, when administered alone or in combination with L. lactis expressing IL-12. To this end, mice were vaccinated by oral route with L. lactis NZ9000 transformed with pSEC derivatives encoding for SOD (pSEC:SOD) and IL-12 (pSEC:scIL-12). In animals receiving L. lactis pSEC:SOD alone, anti-SOD-specific IgM antibodies were detected in sera at day 28 post-vaccination, together with an IgG2a dominated IgG response. SOD-specific sIgA was also detected in nasal and bronchoalveolar lavages. In addition, T-cell-proliferative responses upon re-stimulation with either recombinant SOD or crude Brucella protein extracts were observed up to 6 months after the last boost, suggesting the induction of long term memory. Vaccinated animals were also protected against challenge with the virulent B. abortus 2308 strain. Responses were mildly improved when L. lactis pSEC:SOD was co-administered with L. lactis pSEC:scIL-12. These results indicated that vaccines based on lactococci-derived live carriers are promising interventions against B. abortus infections.

Manipulation of autophagy by bacteria for their own benefit

Autophagy is the host innate immune system's first line of defense against microbial intruders. When the innate defense system recognizes invading bacterial pathogens and their infection processes, autophagic proteins act as cytosolic sensors that allow the autophagic pathway to be rapidly activated. However, many intracellular bacterial pathogens deploy highly evolved mechanisms to evade autophagic recognition, manipulate the autophagic pathway, and remodel the autophagosomal compartment for their own benefit. Here current topics regarding the recognition of invasive bacteria by the cytosolic innate immune system are highlighted, including autophagy and the mechanisms that enable bacteria to evade autophagy. Also highlighted are some selective examples of bacterial activities that manipulate the autophagic pathways for their own benefit.

Brucella adaptation and survival at the crossroad of metabolism and virulence

"In vivo" bacterial nutrition, i.e. the nature of the metabolic network and substrate(s) used by bacteria within their host, is a fundamental aspect of pathogenic or symbiotic lifestyles. A typical example are the Brucella spp., facultative intracellular pathogens responsible for chronic infections of animals and humans. Their virulence relies on their ability to modulate immune response and the physiology of host cells, but the fine-tuning of their metabolism in the host during infection appears increasingly crucial. Here we review new insights on the links between Brucella virulence and metabolism, pointing out the need to investigate both aspects to decipher Brucella infectious strategies.

Course of infection with the emergent pathogen Brucella microti in immunocompromised mice

A new Brucella species, Brucella microti, has been isolated from wild rodents and found to be pathogenic in mice. The biological relevance of this new mouse pathogen is clear, as it allows us to study Brucella infection in a species-specific model. The course of infection in wild-type (wt) and immunodeficient mice that lack B (Jh), T and B (SCID), or T, B, and NK (SCID.Beige) cells was analyzed over 3 weeks. wt mice completely cleared bacteria from the liver and spleen after that time. However, SCID mice showed a much higher bacterial load in the spleen and liver than wt and Jh mice after 1 week and maintained the same level during the next 2 weeks. All mice tested survived for the 3 weeks. In contrast, the bacterial levels in mice that lacked NK cell activity progressively increased and these mice succumbed to infection after 16 to 18 days. Histopathology analysis of infected mice showed extensive areas of necrotic tissue and thrombosis in liver after 1 week in all infected SCID.Beige mice but were not seen in either SCID or wt animals. These processes were dramatically increased after 21 days, corresponding with the death of SCID.Beige animals. Our results indicate that T and/or B cells are required for the control of infection with the mouse pathogen Brucella microti in liver and spleen but that NK cells are crucial for survival in the absence of B and T cells. In addition, they suggest that controlled granuloma formation is critical to clear this type of infection in wt mice.

Protective live oral brucellosis vaccines stimulate Th1 and th17 cell responses

Zoonotic transmission of brucellosis often results from exposure to Brucella-infected livestock, feral animals, or wildlife or frequently via consumption of unpasteurized milk products or raw meat. Since natural infection of humans often occurs by the oral route, mucosal vaccination may offer a means to confer protection for both mucosal and systemic tissues. Significant efforts have focused on developing a live brucellosis vaccine, and deletion of the znuA gene involved in zinc transport has been found to attenuate Brucella abortus. A similar mutation has been adapted for Brucella melitensis and tested to determine whether oral administration of ΔznuA B. melitensis can confer protection against nasal B. melitensis challenge. A single oral vaccination with ΔznuA B. melitensis rapidly cleared from mice within 2 weeks and effectively protected mice upon nasal challenge with wild-type B. melitensis 16M. In 83% of the vaccinated mice, no detectable brucellae were found in their spleens, unlike with phosphate-buffered saline (PBS)-dosed mice, and vaccination also enhanced the clearance of brucellae from the lungs. Moreover, vaccinated gamma interferon-deficient (IFN-γ(-/-)) mice also showed protection in both spleens and lungs, albeit protection that was not as effective as in immunocompetent mice. Although IFN-γ, interleukin 17 (IL-17), and IL-22 were stimulated by these live vaccines, only RB51-mediated protection was codependent upon IL-17 in BALB/c mice. These data suggest that oral immunization with the live, attenuated ΔznuA B. melitensis vaccine provides an attractive strategy to protect against inhalational infection with virulent B. melitensis.

In search of Brucella abortus type IV secretion substrates: screening and identification of four proteins translocated into host cells through VirB system

Type IV secretion systems (T4SS) are specialized protein complexes used by many bacterial pathogens for the delivery of effector molecules that subvert varied host cellular processes. Brucella spp. are facultative intracellular pathogens capable of survival and replication inside mammalian cells. Brucella T4SS (VirB) is essential to subvert lysosome fusion and to create an organelle permissive for replication. One possible role for VirB is to translocate effector proteins that modulate host cellular functions for the biogenesis of the replicative organelle. We hypothesized that proteins with eukaryotic domains or protein-protein interaction domains, among others, would be good candidates for modulation of host cell functions. To identify these candidates, we performed an in silico screen looking for proteins with distinctive features. Translocation of 84 potential substrates was assayed using adenylate cyclase reporter. By this approach, we identified six proteins that are delivered to the eukaryotic cytoplasm upon infection of macrophage-like cells and we could determine that four of them, encoded by genes BAB1_1043, BAB1_2005, BAB1_1275 and BAB2_0123, require a functional T4SS for their delivery. We confirmed VirB-mediated translocation of one of the substrates by immunofluorescence confocal microscopy, and we found that the N-terminal 25 amino acids are required for its delivery into cells.

An evolutionary strategy for a stealthy intracellular Brucella pathogen

Brucella is an intracellular bacterial pathogen that causes abortion and infertility in mammals and leads to a debilitating febrile illness that can progress into a long lasting disease with severe complications in humans. Its virulence depends on survival and replication properties in host cells. In this review, we describe the stealthy strategy used by Brucella to escape recognition of the innate immunity and the means by which this bacterium evades intracellular destruction. We also discuss the development of adaptive immunity and its modulation during brucellosis that in course leads to chronic infections. Brucella has developed specific strategies to influence antigen presentation mediated by cells. There is increasing evidence that Brucella also modulates signaling events during host adaptive immune responses.

Update on the role of innate immune receptors during Brucella abortus infection

The innate immune system constitutes an efficient defense mechanism against invading microbial pathogens. Recent studies have revealed the intracellular signaling cascades involved in the TLR-initiated immune response to Brucella spp. infection. However, there is a piece of the puzzle missing that is the role of non-TLR receptors in innate immunity. The involvement of TLR receptors in brucellosis has been investigated by different research groups. It was demonstrated that TLR2 clearly does not play any role in controlling Brucella abortus infection in vivo, whereas TLR9 has been shown to be required for clearance of this bacterium in infected mice. The participation of adaptor molecules, such as MyD88 and TRIF has also been discussed. Recently, we and others have reported the critical role of MyD88- and not TRIF-mediated signaling in dendritic cell maturation and in vivo resistance during B. abortus infection. However, the relationship between specific Brucella molecules and non-TLR receptors and signal transduction pathways needs to be better understood. It is now clear that the interaction between TLRs and recently identified cytosolic innate immune sensors is crucial for mounting effective immune responses. Finally, this review discusses the mechanisms used by Brucella to escape detection by the host innate immune system.

Brucellosis at the animal/ecosystem/human interface at the beginning of the 21st century

Following the recent discovery of new Brucella strains from different animal species and from the environment, ten Brucella species are nowadays included in the genus Brucella. Although the intracellular trafficking of Brucella is well described, the strategies developed by Brucella to survive and multiply in phagocytic and non-phagocytic cells, particularly to access nutriments during its intracellular journey, are still largely unknown. Metabolism and virulence of Brucella are now considered to be two sides of the same coin. Mechanisms presiding to the colonization of the pregnant uterus in different animal species are not known. Vaccination is the cornerstone of control programs in livestock and although the S19, RB51 (both in cattle) and Rev 1 (in sheep and goats) vaccines have been successfully used worldwide, they have drawbacks and thus the ideal brucellosis vaccine is still very much awaited. There is no vaccine available for pigs and wildlife. Animal brucellosis control strategies differ in the developed and the developing world. Most emphasis is put on eradication and on risk analysis to avoid the re-introduction of Brucella in the developed world. Information related to the prevalence of brucellosis is still scarce in the developing world and control programs are rarely implemented. Since there is no vaccine available for humans, prevention of human brucellosis relies on its control in the animal reservoir. Brucella is also considered to be an agent to be used in bio- and agroterrorism attacks. At the animal/ecosystem/human interface it is critical to reduce opportunities for Brucella to jump host species as already seen in livestock, wildlife and humans. This task is a challenge for the future in terms of veterinary public health, as for wildlife and ecosystem managers and will need a "One Health" approach to be successful.

Contrasting roles of macrophages and dendritic cells in controlling initial pulmonary Brucella infection

Control of pulmonary pathogens constitutes a challenging task as successful immune responses need to be mounted without damaging the lung parenchyma. Using immunofluorescence microscopy and flow cytometry, we analyzed in the mouse the initial innate immune response that follows intranasal inoculation of Brucella abortus. Bacteria were absent from parenchymal dendritic cells (DC) but present in alveolar macrophages in which they replicated. When the number of alveolar macrophages was reduced prior to Brucella infection, small numbers of pulmonary DC were infected and a massive recruitment of TNF-α- and iNOS-producing DC ensued. Coincidentally, Brucella disseminated to the lung-draining mediastinal lymph nodes (LN) where they replicated in both migratory DC and migratory alveolar macrophages. Together, these results demonstrate that alveolar macrophages are critical regulators of the initial innate immune response against Brucella within the lungs and show that pulmonary DC and alveolar macrophages play rather distinct roles in the control of microbial burden.