Brucellosis-associated hepatitis.

AIM: Brucellosis is a zoonotic infection that can affect almost every organ. A mild elevation of aminotransferase levels is usually observed in liver involvement. However, the development of clinical hepatitis is rare. In this study, we aimed to present the hospitalized cases with brucellosis hepatitis in our clinic in a 13-year period. METHODS: A hundred and three patients with significant hepatobiliary involvement, diagnosed by microbiological analysis, were included in the study. For the presence of hepatitis, it was required that the aminotransferases must be ≥ 5 times more than the upper limit and/or the total bilirubin level must be ≥ 2 mg/dl and/or the local hepatic lesion must be demonstrated. RESULTS: Of the cases, 35.9%, 17.5%, and 46.6% had clinical hepatitis, cholestatic hepatitis, and both clinical and cholestatic hepatitis, respectively. The most frequent symptom was fever (85.4%) while the most preferred treatment options were combinations containing aminoglycosides. It was observed that the mean time-interval to decrease to normal values of ALT, AST, and bilirubin values was 15.2 ± 7.8 days while the patients having their treatment regimens. In our study, which focused on liver involvement, it was found that a chronic liver disease did not develop in any of the cases. CONCLUSION: Our study showed that, even in the presence of hepatitis, clinical response and laboratory improvement were high with appropriate treatment. It was observed that the improvement in aminotransferases and total bilirubin values delayed in the cases with blood culture positivity, secondary organ involvement, and alanine aminotransferase/aspartate aminotransferase > 1.

Neurobrucellosis.

PURPOSE OF REVIEW: Brucellosis is one of the most common zoonosis worldwide, affecting 500 000 people, annually. Neurobrucellosis incidence is approximately 4%, and it is almost always heterogeneous. As there are no typical clinical features, its diagnosis is frequently misdiagnosing by other infections. RECENT FINDINGS: Neurobrucellosis picture includes meningitis, meningoencephalitis, encephalitis, cranial neuropathies, intracranial hypertension, sinus thrombosis, hemorrhages radiculitis, peripheral neuropathy, myelitis, and psychiatric manifestations. The diagnosis should be based on symptoms and signs suggestive of neurobrucellosis, not explained by other neurological disease, cerebrospinal fluid analysis, a positive Brucella serology or culture, and a response to specific antibiotics, with a significant improvement of cerebrospinal fluid parameters. SUMMARY: Neurobrucellosis can be insidious, and despite its global distribution, it is still unrecognized and frequently goes unreported. The understanding of the current epidemiology is necessary for eradication of the disease in humans, as well as the disease control in animals and prevention based on occupational hygiene and food hygiene.

Use of the quantum dot-labeled solid lipid nanoparticles for delivery of streptomycin and hydroxychloroquine: A new therapeutic approach for treatment of intracellular Brucella abortus infection.

Brucellosis is considered one of the most important infectious diseases affecting any tissue and organ in the human body. Due to the intracellular pathogenesis of Brucella species, the use of conventional antibiotics for managing chronic brucellosis has several limitations. Therefore, the study focused on the use of solid lipid nanoparticles (SLN) to deliver streptomycin (STR) for intracellular infection, with or without the combination of hydroxychloroquine (HCQ) to evaluate if there might be a boost in the antibiotic effect when using the STR or STR-NPs alone. We used the double emulsion technique to synthesize Nano drug carriers; afterward, the physicochemical characteristics of synthesized Nano drug carriers were determined. The in vitro antibacterial activity of free drugs and Nano drug carriers were evaluated using well diffusion, broth microdilution assays (BMD), and murine macrophage-like cells cell line J774A.1. Additionally, acute and chronic phases of brucellosis were inducted into Wistar rats, and healing capacity of Nano drug carriers on liver and spleen tissues was compared with free drugs. The zeta potential of nanoparticles, means of size, Polydispersity Index (PDI), drugs loading, and encapsulation efficiency were 15.2 mV, 312.5 ± 26 nm, 0.433 ± 0.09, 16.6% and 89.5%, respectively. Well diffusion and BMD methods did not show a significantly differ between free drugs and nano drug carriers. However, the Nano drug carriers remarkably decreased the number of bacteria in the cell line compared to the free drugs. STR/HCQ-SLN enhanced the healing processes of the liver and spleen after brucellosis induction. STR/HCQ-SLN showed better inhibitory effects against the chronic phase of B. abortus infection in comparison to the STR-SLN, but this difference was not statistically significant. Using nanoplatforms to enhance conventional anti-brucellosis agents is promising, green and safe. Due to the continuous release of drugs, drugs increase their accumulation at the site of infection, causing a more significant effect on the chronic and acute phases of brucellosis.

Case report: Revealing a special and rare autoimmune GFAP astrocytopathy in the spinal cord succeeding Neurobrucellosis infection.

Brucellosis, a zoonosis, can cause an inflammatory response in most organs and continues to be a public health problem in some endemic areas, whereas neurobrucellosis is a morbid form of brucellosis that affects the central nervous system (CNS) with poor prognosis. Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is an autoimmune disease, and there have been no reports of a Brucella infection, leading to GFAP astrocytopathy. We report the case of a patient with a positive and high level of GFAP antibodies in the cerebrospinal fluid (CSF), following a Brucella infection. Although this patient did not show any responsible lesions in the diffusion sequence of the magnetic resonant imaging (MRI) scan, we found an evidence of thoracolumbar (T12) involvement on fluorodeoxyglucose (FDG) positron emission tomography (PET). The symptoms of spinal cord involvement were only partly relieved after initial treatment [doxycycline (0.1 g Bid) and rifampicin (0.6 g Qd) for 6 weeks]; however, they markedly improved after the subsequent immunosuppressive therapy [intravenous methylprednisolone (1,000 mg for 3 days)], followed by a 50% reduction from the preceding dose after 3 days, and subsequently, oral prednisone tablets (60 mg/day) was started, which was then gradually tapered [reduced to 10 mg/day every 1-2 weeks)]. The positive response to immunosuppressive therapy and treatment outcome strongly indicated the presence of an autoimmune neurological disease probably triggered by some infectious factors. Therefore, our findings reveal that a Brucella infection is one of the causes of autoimmune GFAP astrocytopathy, and when this infection is difficult to be identified by regular MRI, FDG PET can be used as a supplementary method for diagnosis and treatment.

Splenic abscesses in childhood brucellosis: a case-based review.

OBJECTIVE: Human brucellosis is a zoonosis with an extremely wide spectrum of clinical manifestations. Focal splenic involvement is very uncommon, particularly in the pediatric age group, during the illness' acute phase. CASE REPORT: A 4-year-old boy, already receiving third-generation cephalosporin treatment, was transferred from a local hospital to the University Pediatric Department for fever, anemia, increased inflammation index, and multiple, hyper-echogenic splenic lesions on abdominal ultrasound. Initial diagnostic laboratory investigations for Brucella infection, including the Widal-Wright test, were found to be negative. However, further diagnostic laboratory analysis using the chemiluminescent immunoassay was positive for Brucella IgM antibodies. Treatment with rifampicin at a dose of 150 mg/Kg/twice daily and co-trimethoprim at a dose of 80 mg/Kg/twice daily was started and continued for 7 weeks. IgM antibodies were undetectable after 2 weeks of treatment, and after 6 weeks of treatment, abdominal ultrasound documented a reduction of the diameter of the major splenic infiltrate from 1 to 0.5 cm. At 3 and 5 months of follow-up, re-evaluation of the abdominal lesions displayed complete resolution of the splenic lesions and a complete clinical recovery. CONCLUSIONS: The present case and a literature review are presented in this study since a standard diagnostic laboratory evaluation for brucellosis may miss the diagnosis, and in suspected cases, the laboratory analysis should be extended. Splenic abscesses are known to be rare in brucellosis, but the diagnosis should be considered in children with severe focal lesions, as specific antibiotic treatment may result in complete clinical recovery.

Functional insights into Brucella transcriptional regulator ArsR.

ArsR-family transcriptional factors regulates diverse physiological functions necessary for Brucella adaptation to environmental changes. However, whether the ArsR-family transcriptional regulator are related to virulence, and the precise determination of ArsR direct targets in Brucella are still unknown. Therefore, we created a 2308ΔArsR6 mutant of B. abortus 2308 (S2308). Virulence assay was performed using a murine macrophage cell line (RAW 264.7). We performed chromatin immunoprecipitation of ArsR6 followed by next-generation sequencing (ChIP-seq). We also selected the target gene pobA (BAB2_0600), and created the mutant (2308ΔpobA). The survival capability of 2308ΔpobA strain in RAW 264.7 was detected and the levels of tumor necrosis factor-α (TNF-α), interferon-gamma (IFN-γ), interleukin-12 (IL-12) and interleukin-18 (IL-18) were also measured. The results showed that 2308ΔArsR6 reduced survival capability in RAW 264.7. We detected 40 intergenic ChIP-seq peaks of ArsR6 binding distributed across the Brucella genome. 2308ΔpobA was significantly reduced survival capability in RAW 264.7. After the macrophages were infected with 2308ΔpobA, the levels of TNF-α, IFN-γ, IL-12 and IL-18 were decreased and were significantly lower than that for the S2308-infected group, indicating that the 2308ΔpobA could reduce the secretion of inflammatory cytokines. Taken together, the research provided new insights into the functionality of ArsR6 and great significance to clarify the function of ArsR6.

A Brucella Omp16 Conditional Deletion Strain Is Attenuated in BALB/c Mice.

Brucella spp. are facultative intracellular pathogens that invade, survive and proliferate in numerous phagocytic and non-phagocytic cell types, thereby leading to human and animal brucellosis. Outer membrane proteins (Omps) are major immunogenic and protective antigens that are implicated in Brucella virulence. A strain deleted of the omp16 gene has not been obtained which suggests that the Omp16 protein is vital for Brucella survival. Nevertheless, we previously constructed an omp16 conditional deletion strain of Brucella, ΔOmp16. Here, the virulence and immune response elicted by this strain were assessed in a mouse model of infection. Splenomegaly was significantly reduced at two weeks post-infection in ΔOmp16-infected mice compared to infection with the parental strain. The bacterial load in the spleen also was significantly decreased at this post-infection time point in ΔOmp16-infected mice. Histopathological changes in the spleen were observed via hematoxylineosin staining and microscopic examination which showed that infection with the ΔOmp16 strain alleviated spleen histopathological alterations compared to mice infected with the parental strain. Moreover, the levels of humoral and cellular immunity were similar in both ΔOmp16-infected mice and parental strain-infected mice. The results overall show that the virulence of ΔOmp16 is attenuated markedly, but that the immune responses mediated by the deletion and parental strains in mice are indistinguishable. The data provide important insights that illuminate the pathogenic strategies adopted by Brucella.

A rare case of thoracic brucellosis misdiagnosed as malignant tumor and literature review.

Brucellosis remains a major public health problem worldwide. It is commonly found in most developed and developing countries, such as the Mediterranean region, the Middle East, and Latin America. In China, brucellosis is mainly distributed in some of the northern provinces and is relatively rare in Shandong province. Brucellosis has a variety of clinical manifestations, with fever, sweating, fatigue, and migratory joint pain being the most common. Because of the non-specific clinical symptoms, brucellosis is often misdiagnosed as other diseases. Here, we report a rare case of brucellosis of thoracic vertebrae misdiagnosed as thoracic malignant tumor and present a review of related literature.

Omp31 of Brucella Inhibits NF-κB p65 Signaling Pathway by Inducing Autophagy in BV-2 Microglia.

Neurobrucellosis is a serious central nervous system (CNS) inflammatory disorder caused by Brucella, and outer membrane protein-31 (Omp31) plays an important role in Brucella infection. This study aims to determine whether Omp31 can induce autophagy in BV-2 microglia. Another goal of the study is to further examine the effect of autophagy on the nuclear transcription factor κB (NF-κB) p65 signaling pathway. We observed that Omp31 stimulated autophagy by increasing microtubule-associated protein 1 light chain 3B (LC3B-II) levels and inducing autophagosome formation at 6 h and 12 h. Concomitantly, Omp31 induced tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) expression in a time-dependent manner but reduced the expression of TNF-α at 6 h. We utilized Omp31 with or without rapamycin or 3-methyladenine (3-MA) to treat BV-2 microglia, and it demonstrated further that Omp31 induced autophagy by promoting LC3B-II, Beclin-1 proteins expression and inhibiting the p62 protein levels. Furthermore, we explored the effects of autophagy on the NF-κB p65 pathway through western blot analysis, RT-qPCR assay, enzyme-linked immunosorbent assay (ELISA) and immunofluorescence. The data suggest that Omp31 as well as rapamycin, the autophagy inducer, can decrease TNF-α levels through the inhibition of the NF-κB p65 signaling pathway. Taken together, Omp31 can function as a catalyst in both autophagy induction and NF-κB p65 signal inhibition. Furthermore, Omp31-induced autophagy may inhibit the expression of TNF-α by negatively regulating NF-κB p65 signaling pathway.

A Sinorhizobium meliloti and Agrobacterium tumefaciens ExoR ortholog is not crucial for Brucella abortus virulence.

Brucella is a facultative extracellular-intracellular pathogen that belongs to the Alphaproteobacteria class. Precise sensing of environmental changes and a proper response mediated by a gene expression regulatory network are essential for this pathogen to survive. The plant-related Alphaproteobacteria Sinorhizobium meliloti and Agrobacterium tumefaciens also alternate from a free to a host-associated life, where a regulatory invasion switch is needed for this transition. This switch is composed of a two-component regulatory system (TCS) and a global inhibitor, ExoR. In B. abortus, the BvrR/BvrS TCS is essential for intracellular survival. However, the presence of a TCS inhibitor, such as ExoR, in Brucella is still unknown. In this work, we identified a genomic sequence similar to S. meliloti exoR in the B. abortus 2308W genome, constructed an exoR mutant strain, and performed its characterization through ex vivo and in vivo assays. Our findings indicate that ExoR is related to the BvrR phosphorylation state, and is related to the expression of known BvrR/BrvS gene targets, such as virB8, vjbR, and omp25 when grown in rich medium or starving conditions. Despite this, the exoR mutant strain showed no significant differences as compared to the wild-type strain, related to resistance to polymyxin B or human non-immune serum, intracellular replication, or infectivity in a mice model. ExoR in B. abortus is related to BvrR/BvrS as observed in other Rhizobiales; however, its function seems different from that observed for its orthologs described in A. tumefaciens and S. meliloti.

A case report of endocarditis and spondylitis caused by Brucella melitensis biovar 3.

BACKGROUND: This case report describes the clinical process of a shepherd who suffered brucellosis-related endocarditis (BE) and spondylitis (BS) and was infected with Brucella melitensis biovar 3 (B. melitensis biovar 3). CASE PRESENTATION: A 55-year-old male patient was admitted to The First Affiliated Hospital of Shihezi University on October 11, 2018, due to over 3 months of intermittent fever, back pain, and heart trouble. The Rose Bengal Plate test was positive, the standard agglutination test titer for brucellosis was 1/800, and the blood culture was positive for B. melitensis biovar 3. Three instances of transthoracic echocardiography examination at days 1, 25, and 376 after admission to the hospital and magnetic resonance imaging (MRI) and computed tomography (CT) checks at days 5 and 38 revealed that the size of the vegetation on the posterior leaflet of the mitral valve increased from 0.7 × 1.4 cm to 1.2 × 1.5 cm and that the left atrium and ventricle were enlarged. The MRI and CT results showed hyperplasia of the second and third vertebra, a cold abscess formed on both sides of the psoas major muscles, and the vertebra hyperplasia became aggravated at a later time point. The patient's situation deteriorated, and heart failure was discovered on October 22, 2019. At the moment of submission of this manuscript, the patient remains in bed at home because of severe debility caused by brucellosis. CONCLUSIONS: This is the first reported case of endocarditis combined with spondylitis caused by B. melitensis biovar 3 in a shepherd. Brucellosis infection can cause work-power losses because of misdiagnosis or a lack of proper treatment. Early diagnosis and treatment are essential for a successful outcome.

Characterization of Brucella abortus S19 as a challenge strain for use in a mouse model of brucellosis.

The objective of this project was to conduct a feasibility study to determine whether the Brucella abortus S19 vaccine infects and persists in mice and determine whether S19 can be used as a challenge strain for vaccine trial studies. Groups of BALB/c mice were inoculated (intraperitoneally, subcutaneously, intranasally) and euthanized to determine colonization titers in the spleens and lungs. This study showed that S19 does infect and persist in the tissues of mice for 8 weeks and demonstrates that S19 can be used, safely and economically under BSL2 containment, as the challenge strain for future trials to evaluate vaccine efficacy.

Uncovering the Hidden Credentials of Brucella Virulence.

Bacteria in the genus Brucella are important human and veterinary pathogens. The abortion and infertility they cause in food animals produce economic hardships in areas where the disease has not been controlled, and human brucellosis is one of the world's most common zoonoses. Brucella strains have also been isolated from wildlife, but we know much less about the pathobiology and epidemiology of these infections than we do about brucellosis in domestic animals. The brucellae maintain predominantly an intracellular lifestyle in their mammalian hosts, and their ability to subvert the host immune response and survive and replicate in macrophages and placental trophoblasts underlies their success as pathogens. We are just beginning to understand how these bacteria evolved from a progenitor alphaproteobacterium with an environmental niche and diverged to become highly host-adapted and host-specific pathogens. Two important virulence determinants played critical roles in this evolution: (i) a type IV secretion system that secretes effector molecules into the host cell cytoplasm that direct the intracellular trafficking of the brucellae and modulate host immune responses and (ii) a lipopolysaccharide moiety which poorly stimulates host inflammatory responses. This review highlights what we presently know about how these and other virulence determinants contribute to Brucella pathogenesis. Gaining a better understanding of how the brucellae produce disease will provide us with information that can be used to design better strategies for preventing brucellosis in animals and for preventing and treating this disease in humans.

Dexamethasone-induced stress exacerbates shedding, tissue antigen distribution, and pathology of caprine Brucellosis.

This study investigated dexamethasone-treatment, shedding routes, tissue antigen distribution, and pathology of caprine Brucellosis. Eighteen non-pregnant goats were randomly grouped into A, B, and C. Group A was administered dexamethasone for 7 days at 2 mg/kg before inoculating 0.5 mL B. melitensis at 107 CFU ocularly while group B was inoculated 0.5 mL B. melitensis only, and C as control negative. Blood samples, ocular, nasal, and vaginal swabs were obtained for evaluation. Three goats were sacrificed from each group at days 21 and 42 post-inoculation (pi) and selected tissues collected for PCR, histopathology, and immunohistochemistry. Brucella melitensis was detected in the ocular swabs of group A significantly higher than group B. Shedding was prolonged in group A compared to B. The overall shedding was 22.2% in group A and 9.4% in group B. The uterus of both groups A and B revealed mild inflammation and microgranuloma, extensive necrotic lesions in lymph nodes. Liver showed multifocal necrosis predominantly in group A. Lesion scoring showed significantly higher scores in A compared to B. Strong immunostaining was observed in the liver, lungs, and spleen, predominantly at day 21 pi. This study demonstrated dexamethasone prolonged shedding, tissue antigen distribution, and pathology in dexamethasone-treated goats.

Seroprevalence of brucellosis in small ruminants and related risk behaviours among humans in different husbandry systems in Mali.

Mali has a high pastoral potential with diverse coexisting production systems ranging from traditional (nomadic, transhumant, sedentary) to commercial (fattening and dairy production) production systems. Each of those systems is characterised by close interactions between animals and humans, increasing the potential risk of transmission of zoonotic diseases. The nature of contact network suggests that the risks may vary according to species, production systems and behaviors. However, the study of the link between small ruminants and zoonotic diseases has received limited attention in Mali. The objective of this study was to assess brucellosis seroprevalence and determine how the husbandry systems and human behaviour expose animal and human to infection risk. A cross-sectional study using cluster sampling was conducted in three regions in Mali. Blood was collected from 860 small ruminants. The sera obtained were analysed using both Rose Bengal and cELISA tests. In addition, 119 farmers were interviewed using a structured questionnaire in order to identify the characteristics of farms as well as the risk behaviors of respondents. Husbandry systems were dominated by agro-pastoral systems followed by pastoral systems. The commercial farms (peri-urban and urban) represent a small proportion. Small ruminant individual seroprevalence was 4.1% [2.8-5.6% (95% CI)]. Herd seroprevalence was estimated at 25.2% [17.7-33.9% (95% CI)]. Peri-urban farming system was more affected with seroprevalence of 38.1% [18.1-61.5 (95% CI)], followed by pastoral farming system (24.3% [11.7-41.2 (95% CI)]). Identified risk behaviors of brucellosis transmission to animals were: exchange of reproductive males (30.2%); improper disposal of placentas in the farms (31.1%); and keeping aborted females in the herd (69.7%). For humans, risk factors were: close and prolonged contact with animals (51.2%); consumption of unpasteurized dairy products (26.9%); and assisting female animals during delivery without any protection (40.3%). This study observed a high seroprevalence of brucellosis in small ruminants and also identified risky practices that allow cross transmission between the two populations. This calls for control strategy using a multi-sectoral and multidimensional approach.

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.

Hepatic and splenic immune response during acute vs. chronic Brucella melitensis infection using in situ microscopy.

Brucella melitensis is an intracellular bacteria causing disease in humans as an incidental host. The infection initiates as acute flu-like symptoms and may transform into a chronic cyclic infection. This cyclic infection may be partly due to the bacteria's ability to persist within antigen presenting cells and evade the CD8 + T cell response over long periods of time. This research aims to characterize the immune response of the acute and chronic forms of brucellosis in the murine liver and spleen. We also sought to determine if the exhaustion of the CD8 + T cells was a permanent or temporary change. This was accomplished by using adoptive transfer of acutely infected CD8 + T cells and chronically infected CD8 + T cells into a naïve host followed by re-infection. The histological examination presented supports the concept that exhausted T-cells can regain function through evidence of granulomatous inflammation after virulent challenge in a new host environment.

Omp16, a conserved peptidoglycan-associated lipoprotein, is involved in Brucella virulence in vitro.

Brucella, the bacterial agent of common zoonotic brucellosis, primarily infects specific animal species. The Brucella outer membrane proteins (Omps) are particularly attractive for developing vaccine and improving diagnostic tests and are associated with the virulence of smooth Brucella strains. Omp16 is a homologue to peptidoglycan-associated lipoproteins (Pals), and an omp16 mutant has not been generated in any Brucella strain until now. Very little is known about the functions and pathogenic mechanisms of Omp16 in Brucella. Here, we confirmed that Omp16 has a conserved Pal domain and is highly conserved in Brucella. We attempted to delete omp16 in Brucella suis vaccine strain 2 (B. suis S2) without success, which shows that Omp16 is vital for Brucella survival. We acquired a B. suis S2 Omp16 mutant via conditional complementation. Omp16 deficiency impaired Brucella outer membrane integrity and activity in vitro. Moreover, inactivation of Omp16 decreased bacterial intracellular survival in macrophage RAW 264.7 cells. B. suis S2 and its derivatives induced marked expression of IL-1ß, IL-6, and TNF-a mRNA in Raw 264.7 cells. Whereas inactivation of Omp16 in Brucella enhanced IL-1ß and IL-6 expression in Raw 264.7 cells. Altogether, these findings show that the Brucella Omp16 mutant was obtained via conditional complementation and confirmed that Omp16 can maintain outer membrane integrity and be involved in bacterial virulence in Brucella in vitro and in vivo. These results will be important in uncovering the pathogenic mechanisms of Brucella.