Dendritic cells and Brucella spp. interaction: the sentinel host and the stealthy pathogen

Deletion of the alr gene in Brucella suis S2 attenuates virulence by enhancing TLR4-NF-κB-NLRP3- mediated host inflammatory responses

Brucella is an intracellular parasitic bacterium lacking typical virulence factors, and its pathogenicity primarily relies on replication within host cells. In this study, we observed a significant increase in spleen weight in mice immunized with a Brucella strain deleted of the gene for alanine racemase (Alr), the enzyme responsible for alanine racemization (Δalr). However, the bacterial load in the spleen markedly decreased in the mutant strain. Concurrently, the ratio of white pulp to red pulp in the spleen was increased, serum IgG levels were elevated, but no significant damage to other organs was observed. In addition, the inflammatory response was potentiated and the NF-κB-NLRP3 signaling pathway was activated in macrophages (RAW264.7 Cells and Bone Marrow-Derived Cells) infect ed with the Δalr mutant. Further investigation revealed that the Δalr mutant released substantial amounts of protein in a simulated intracellular environment which resulted in heightened inflammation and activation of the TLR4-NF-κB-NLRP3 pathway in macrophages. The consequent cytoplasmic exocytosis reduced intracellular Brucella survival. In summary, cytoplasmic exocytosis products resulting from infection with a Brucella strain deleted of the alr gene effectively activated the TLR4-NFκB-NLRP3 pathway, triggered a robust inflammatory response, and reduced bacterial survival within host cells. Moreover, the Δalr strain exhibits lower toxicity and stronger immunogenicity in mice.

Brucella infection and Toll-like receptors

Brucella consists of gram-negative bacteria that have the ability to invade and replicate in professional and non-professional phagocytes, and its prolonged persistence in the host leads to brucellosis, a serious zoonosis. Toll-like receptors (TLRs) are the best-known sensors of microorganisms implicated in the regulation of innate and adaptive immunity. In particular, TLRs are transmembrane proteins with a typical structure of an extracellular leucine-rich repeat (LRR) region and an intracellular Toll/interleukin-1 receptor (TIR) domain. In this review, we discuss Brucella infection and the aspects of host immune responses induced by pathogens. Furthermore, we summarize the roles of TLRs in Brucella infection, with substantial emphasis on the molecular insights into its mechanisms of action.

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 .

Post-transcriptional control of the essential enzyme MurF by a small regulatory RNA in Brucella abortus

Brucella abortus is a facultative, intracellular, zoonotic pathogen that resides inside macrophages during infection. This is a specialized niche where B. abortus encounters various stresses as it navigates through the macrophage. In order to survive this harsh environment, B. abortus utilizes post-transcriptional regulation of gene expression through the use of small regulatory RNAs (sRNAs). Here, we characterize a Brucella sRNAs called MavR (for MurF- and virulence-regulating sRNA), and we demonstrate that MavR is required for the full virulence of B. abortus in macrophages and in a mouse model of chronic infection. Transcriptomic and proteomic studies revealed that a major regulatory target of MavR is MurF. MurF is an essential protein that catalyzes the final cytoplasmic step in peptidoglycan (PG) synthesis; however, we did not detect any differences in the amount or chemical composition of PG in the ΔmavR mutant. A 6-nucleotide regulatory seed region within MavR was identified, and mutation of this seed region resulted in dysregulation of MurF production, as well as significant attenuation of infection in a mouse model. Overall, the present study underscores the importance of sRNA regulation in the physiology and virulence of Brucella.

When the Going Gets Rough: The Significance of Brucella Lipopolysaccharide Phenotype in Host-Pathogen Interactions

Brucella is a facultatively intracellular bacterial pathogen and the cause of worldwide zoonotic infections, infamous for its ability to evade the immune system and persist chronically within host cells. Despite the frequent association with attenuation in other Gram-negative bacteria, a rough lipopolysaccharide phenotype is retained by Brucella canis and Brucella ovis, which remain fully virulent in their natural canine and ovine hosts, respectively. While these natural rough strains lack the O-polysaccharide they, like their smooth counterparts, are able to evade and manipulate the host immune system by exhibiting low endotoxic activity, resisting destruction by complement and antimicrobial peptides, entering and trafficking within host cells along a similar pathway, and interfering with MHC-II antigen presentation. B. canis and B. ovis appear to have compensated for their roughness by alterations to their outer membrane, especially in regards to outer membrane proteins. B. canis, in particular, also shows evidence of being less proinflammatory in vivo, suggesting that the rough phenotype may be associated with an enhanced level of stealth that could allow these pathogens to persist for longer periods of time undetected. Nevertheless, much additional work is required to understand the correlates of immune protection against the natural rough Brucella spp., a critical step toward development of much-needed vaccines. This review will highlight the significance of rough lipopolysaccharide in the context of both natural disease and host–pathogen interactions with an emphasis on natural rough Brucella spp. and the implications for vaccine development.

Pathogenesis of Brucella epididymoorchitis-game of Brucella death

Brucellosis is a worldwide zoonotic disease caused by Brucella spp. Human infection often results from direct contact with tissues from infected animals or by consumption of undercooked meat and unpasteurised dairy products, causing serious economic losses and public health problems. The male genitourinary system is a common involved system in patients with brucellosis. Among them, unilateral orchitis and epididymitis are the most common. Although the clinical and imaging aspect of orchi-epididymitis caused by brucellosis have been widely described, the cellular and molecular mechanisms involved in the damage and the immune response in testis and epididymis have not been fully elucidated. In this review, we first summarised the clinical characteristics of Brucella epididymo-orchitis and the composition of testicular and epididymal immune system. Secondly, with regard to the mechanism of Brucella epididymoorchitis, we mainly discussed the process of Brucella invading testis and epididymis in temporal and spatial order, including i) Brucella evades innate immune recognition of testicular PRRs；ii) Brucella overcomes the immune storm triggered by the invasion of testis through bacterial lipoproteins and virulence factors, and changes the secretion mode of cytokines; iii) Brucella breaks through the blood-testis barrier with the help of macrophages, and inflammatory cytokines promote the oxidative stress of Sertoli cells, damaging the integrity of BTB; iv) Brucella inhibits apoptosis of testicular phagocytes. Finally, we revealed the structure and sequence of testis invaded by Brucella at the tissue level. This review will enable us to better understand the pathogenesis of orchi-epididymitis caused by brucellosis and shed light on the development of new treatment strategies for the treatment of brucellosis and the prevention of transition to chronic form. Facing the testicle with immunity privilege, Brucella is like Bruce Lee in the movie Game of Death, winning is survival while losing is death.HIGHLIGHTSWe summarized the clinical features and pathological changes of Brucellaepididymoorchitis.Our research reveals the pathogenesis of Brucella epididymoorchitis, which mainly includes the subversion of testicular immune privilege by Brucella and a series of destructive reactions derived from it.As a basic framework and valuable resource, this study can promote the exploration of the pathogenesis of Brucella and provide reference for determining new therapeutic targets for brucellosis in the future.

Bacteriophage therapy for inhibition of multi drug-resistant uropathogenic bacteria: a narrative review

Multi-Drug Resistant (MDR) uropathogenic bacteria have increased in number in recent years and the development of new treatment options for the corresponding infections has become a major challenge in the field of medicine. In this respect, recent studies have proposed bacteriophage (phage) therapy as a potential alternative against MDR Urinary Tract Infections (UTI) because the resistance mechanism of phages differs from that of antibiotics and few side effects have been reported for them. Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis are the most common uropathogenic bacteria against which phage therapy has been used. Phages, in addition to lysing bacterial pathogens, can prevent the formation of biofilms. Besides, by inducing or producing polysaccharide depolymerase, phages can easily penetrate into deeper layers of the biofilm and degrade it. Notably, phage therapy has shown good results in inhibiting multiple-species biofilm and this may be an efficient weapon against catheter-associated UTI. However, the narrow range of hosts limits the use of phage therapy. Therefore, the use of phage cocktail and combination therapy can form a highly attractive strategy. However, despite the positive use of these treatments, various studies have reported phage-resistant strains, indicating that phage–host interactions are more complicated and need further research. Furthermore, these investigations are limited and further clinical trials are required to make this treatment widely available for human use. This review highlights phage therapy in the context of treating UTIs and the specific considerations for this application.

The Mechanism of Facultative Intracellular Parasitism of Brucella

Brucellosis is a highly prevalent zoonotic disease characterized by abortion and reproductive dysfunction in pregnant animals. Although the mortality rate of Brucellosis is low, it is harmful to human health, and also seriously affects the development of animal husbandry, tourism and international trade. Brucellosis is caused by Brucella, which is a facultative intracellular parasitic bacteria. It mainly forms Brucella-containing vacuoles (BCV) in the host cell to avoid the combination with lysosome (Lys), so as to avoid the elimination of it by the host immune system. Brucella not only has the ability to resist the phagocytic bactericidal effect, but also can make the host cells form a microenvironment which is conducive to its survival, reproduction and replication, and survive in the host cells for a long time, which eventually leads to the formation of chronic persistent infection. Brucella can proliferate and replicate in cells, evade host immune response and induce persistent infection, which are difficult problems in the treatment and prevention of Brucellosis. Therefore, the paper provides a preliminary overview of the facultative intracellular parasitic and immune escape mechanisms of Brucella, which provides a theoretical basis for the later study on the pathogenesis of Brucella.

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.

Functional analysis of Bucella reveals transcriptional regulation of MarR

Brucellosis is a zoonotic infectious disease caused by Brucella infection. MarR-family transcription factors are closely related to diverse physiological functions necessary for many pathogens adaptation to environmental changes. However, whether the MarR-family transcription factors are involved in virulence, mediated inflammatory responses and regulated virulence gene expression in the intracellular pathogen Brucella are still unknown. Therefore, we created a 2308ΔMarR6 mutant of B. abortus 2308 (S2308). Virulence and inflammatory cytokines assays were performed using a murine macrophage cell line (RAW 264.7). We also performed chromatin immunoprecipitation of MarR6 followed by next-generation sequencing (ChIP-seq). The results showed that 2308ΔMarR6 was significantly reduced survival capability in RAW 264.7. After the macrophages were infected with 2308ΔMarR6, the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-12 (IL-12), interferon-gamma (IFN-γ) and macrophage chemoattractant protein-1 (MCP-1) were decreased and were significantly lower than that for the S2308-infected group, indicating that the 2308ΔMarR6 mutant could reduce the secretion of inflammatory cytokines. Furthermore, we detected 122 intergenic ChIP-seq peaks of MarR6 binding distributed across the Brucella genome. Taken together, the research has recorded valuable data about MarR6. Our findings are of great significance in elucidating the function of MarR6.