Mycobacterium tuberculosis protein Rv2652c enhances intracellular survival by inhibiting host immune responses.

BACKGROUNDS: Mycobacterium tuberculosis (Mtb), the pathogen responsible for tuberculosis, secretes a multitude of proteins that modulate the host's immune response to ensure its own persistence. The region of difference (RD) genes encoding proteins play key roles in TB immunity and pathogenesis. Nevertheless, the roles of the majority of RD-encoded proteins remain to be elucidated. OBJECTS: To elucidate the role of Rv2652c located in RD13 in Mtb on bacterial growth, bacterial survival, and host immune response. METHODS: We constructed the strain MS_Rv2652c which over-expresses Mtb RD-encoding protein Rv2652c in M. smegmatis (MS), and compared it with the wild strain in the bacterial growth, bacterial survival, virulence of Rv2652c, and determined the effect of MS_Rv2652c on host immune response in macrophages. RESULTS: Rv2652c protein is located at cell wall of MS_Rv2652c strain and also an integral component of the Mtb H37Rv cell wall. Rv2652c can enhance the resistance of recombinant MS to various stressors. Moreover, Rv2652c inhibits host proinflammatory responses via modulation of the NF-κB pathway, thereby promoting Mtb survival in vitro and in vivo. CONCLUSION: Our data suggest that cell wall protein Rv2652c plays an important role in creating a favorable environment for bacterial survival by modulating host signals and could be established as a potential TB drug target.

Brucella rough RB51 infection activates P53-Slc7a11-Gpx4/GSH pathway to induce ferroptosis to attenuate the intracellular survival on macrophages.

B. abortus is a facultative intracellular bacterium that replicates within macrophages. Intracellular survival is one of the important indexes to evaluate the virulence of Brucella. Ferroptosis is a type of programmed cell death induced by the accumulation of free iron, reactive oxygen species (ROS), and toxic lipid peroxides, play roles on cancers, cardiovascular diseases, and inflammatory diseases. In this study, we found that Brucella rough strain RB51 induced ferroptosis on macrophages with reduced levels of host glutathione and glutathione peroxidase 4 (Gpx4), together with increased ferrous iron, lipid peroxidation, and ROS. The inhibitor ferrostatin-1 significantly reduced the ferroptosis of RB51-infected macrophages, confirming that ferroptosis occurred during infection with Brucella RB51. Furthermore, we found that RB51 infection induced ferroptosis is regulated by P53-Slc7a11-Gpx4/GSH signal pathway. Inhibiting P53 decreased the levels of ROS and lipid peroxidation, while the levels of Slc7a11, Gpx4 and GSH were rescued. More importantly, inhibiting ferroptosis by different ferroptosis inhibitors increased the intracellular survival of Brucella RB51, indicating ferroptosis functions on the attenuation of Brucella intracellular survival. Collectively, our observations demonstrate that Brucella RB51 infection induces ferroptosis on macrophages, which is regulated by P53-Slc7a11-Gpx4/GSH signal pathway and functions on the attenuation of intracellular survival of Brucella.

Suppressing Mycobacterium tuberculosis virulence and drug resistance by targeting Eis protein through computational drug discovery.

Tuberculosis (TB) remains a critical health threat, particularly with the emergence of multidrug-resistant strains. This demands attention from scientific communities and healthcare professionals worldwide to develop effective treatments. The enhanced intracellular survival (Eis) protein is an acetyltransferase enzyme of Mycobacterium tuberculosis that functions by adding acetyl groups to aminoglycoside antibiotics, which interferes with their ability to bind to the bacterial ribosome, thereby preventing them from inhibiting protein synthesis and killing the bacterium. Therefore, targeting this protein accelerates the chance of restoring the aminoglycoside drug activity, thereby reducing the emergence of drug-resistant TB. For this, we have screened 406,747 natural compounds from the Coconut database against Eis protein. Based on MM/GBSA rescoring binding energy, the top 5 most prominent natural compounds, viz. CNP0187003 (- 96.14 kcal/mol), CNP0176690 (- 93.79 kcal/mol), CNP0136537 (- 92.31 kcal/mol), CNP0398701 (- 91.96 kcal/mol), and CNP0043390 (- 91.60 kcal/mol) were selected. These compounds exhibited the presence of a substantial number of hydrogen bonds and other significant interactions confirming their strong binding affinity with the Eis protein during the docking process. Subsequently, the MD simulation of these compounds exhibited that the Eis-CNP0043390 complex was the most stable, followed by Eis-CNP0187003 and Eis-CNP0176690 complex, further verified by binding free energy calculation, principal component analysis (PCA), and Free energy landscape analysis. These compounds demonstrated the most favourable results in all parameters utilised for this investigation and may have the potential to inhibit the Eis protein. There these findings will leverage computational techniques to identify and develop a natural compound inhibitor as an alternative for drug-resistant TB.

Intracellular Survival and Pathogenicity Modulation of Salmonella Lon, CpxR, and RfaL Mutants Used as Live Bacterial Vectors under Abiotic Stress, Unveiling the Link between Stress Response and Virulence in Epithelial Cells.

In the current study, two Salmonella Typhimurium strains, JOL 912 and JOL 1800, were engineered from the wild-type JOL 401 strain through in-frame deletions of the lon and cpxR genes, with JOL 1800 also lacking rfaL. These deletions significantly attenuated the strains, impairing their intracellular survival and creating unique immunological profiles. This study investigates the response of these strains to various abiotic stress conditions commonly experienced in vivo, including temperature, acidity, osmotic, and oxidative stress. Notably, cold stress induced a non-significant trend towards increased invasion by Salmonella compared to other stressors. Despite the observed attenuation, no significant alterations in entry mechanisms (trigger vs. zipper) were noted between these strains, although variations were evident depending on the host cell type. Both strains effectively localized within the cytoplasm, demonstrating their ability to invade and interact with the intracellular environment. Immunologically, JOL 912 elicited a robust response, marked by substantial activation of nuclear factor kappa B (NF-kB), and chemokines, interleukin 8 (CXCL 8) and interleukin 10 (CXCL 10), comparable to the wild-type JOL 401 (over a fourfold increase compared to JOL 1800). In contrast, JOL 1800 exhibited a minimal immune response. Additionally, these attenuations influenced the expression of cyclins D1 and B1 and caspases 3 and 7, indicating cell cycle arrest at the G2/M phase and promotion of the G0/G1 to S phase transition, alongside apoptosis in infected cells. These findings provide valuable insights into the mechanisms governing the association, internalization, and survival of Salmonella mutants, enhancing our understanding of their regulatory effects on host cell physiology.

Intracellular Streptococcus pneumoniae develops enhanced fluoroquinolone persistence during influenza A coinfection.

Streptococcus pneumoniae is a major pathogen responsible for severe complications in patients with prior influenza A virus (IAV) infection. We have previously demonstrated that S. pneumoniae exhibits increased intracellular survival within IAV-infected cells. Fluoroquinolones (FQs) are widely used to treat pneumococcal infections. However, our prior work has shown that S. pneumoniae can develop intracellular FQ persistence, a phenomenon triggered by oxidative stress within host cells. This persistence allows the bacteria to withstand high FQ concentrations. In this study, we show that IAV infection enhances pneumococcal FQ persistence during intracellular survival within pneumocytes, macrophages, and neutrophils. This enhancement is partly due to increased oxidative stress induced by the viral infection. We find that this phenotype is particularly pronounced in autophagy-proficient host cells, potentially resulting from IAV-induced blockage of autophagosome-lysosome fusion. Moreover, we identified several S. pneumoniae genes involved in oxidative stress response that contribute to FQ persistence, including sodA (superoxide dismutase), clpL (chaperone), nrdH (glutaredoxin), and psaB (Mn+2 transporter component). Our findings reveal a novel mechanism of antibiotic persistence promoted by viral infection within host cells. This underscores the importance of considering this phenomenon when using FQs to treat pneumococcal infections, especially in patients with concurrent influenza A infection.

Mycobacterium tuberculosis FadD18 Promotes Proinflammatory Cytokine Secretion to Inhibit the Intracellular Survival of Bacillus Calmette-Guérin.

Mycobacterium tuberculosis causes 6.4 million cases of tuberculosis and claims 1.6 million lives annually. Mycobacterial adhesion, invasion of host cells, and subsequent intracellular survival are crucial for the infection and dissemination process, yet the cellular mechanisms underlying these phenomena remain poorly understood. This study created a Bacillus Calmette-Guérin (BCG) transposon library using a MycomarT7 phage carrying a Himar1 Mariner transposon to identify genes related to mycobacteria adhesion and invasion. Using adhesion and invasion model screening, we found that the mutant strain B2909 lacked adhesion and invasion abilities because of an inactive fadD18 gene, which encodes a fatty-acyl CoA ligase, although the specific function of this gene remains unclear. To investigate the role of FadD18, we constructed a complementary strain and observed that fadD18 expression enhanced the colony size and promoted the formation of a stronger cord-like structure; FadD18 expression also inhibited BCG growth and reduced BCG intracellular survival in macrophages. Furthermore, FadD18 expression elevated levels of the proinflammatory cytokines IL-6, IL-1ß, and TNF-α in infected macrophages by stimulating the NF-κB and MAPK signaling pathways. Overall, the FadD18 plays a key role in the adhesion and invasion abilities of mycobacteria while modulating the intracellular survival of BCG by influencing the production of proinflammatory cytokines.

BPP0974 is a Bordetella parapertussis adhesin expressed in the avirulent phase, implicated in biofilm formation and intracellular survival.

B. parapertussis is a bacterium that causes whooping cough, a severe respiratory infection disease, that has shown an increased incidence in the population. Upon transmission through aerosol droplets, the initial steps of host colonization critically depend on the bacterial adhesins. We here described BPP0974, a B. parapertussis protein that exhibits the typical domain architecture of the large repetitive RTX adhesin family. BPP0974 was found to be retained in the bacterial membrane and secreted into the culture medium. This protein was found overexpressed in the avirulent phase of B. parapertussis, the phenotype proposed for initial host colonization. Interestingly, BPP0974 was found relevant for the biofilm formation as well as involved in the bacterial attachment to and survival within the respiratory epithelial cells. Taken together, our results suggest a role for BPP0974 in the early host colonization and pathogenesis of B. parapertussis.

Insights into the effect of guanylate-binding protein 1 on the survival of Brucella intracellularly.

Brucellosis is a zoonotic disease that affects wild and domestic animals. It is caused by members of the bacterial genus Brucella. Guanylate-binding protein 1 (GBP1) is associated with microbial infections. However, the role of GBP1 during Brucella infection remains unclear. This investigation aimed to identify the association of GBP1 with brucellosis. Results showed that Brucella infection induced GBP1 upregulation in RAW 264.7 murine macrophages. Small interfering GBP1 targeting RNAs were utilized to explore how GBP1 regulates the survival of Brucella intracellularly. Results revealed that GBP1 knockdown promoted Brucella's survival ability, activated Nod-like receptor (NLR) containing a pyrin domain 3 (NLRP3) and absent in melanoma 2 (AIM2) inflammatory corpuscles, and induced pro-inflammatory cytokines IFN-γ and IL-1ß. Furthermore, Brucella stimulated the expression of GBP1 in bone marrow-derived macrophages (BMDMs) and mice. During the inhibition of GBP1 in BMDMs, the intracellular growth of Brucella increased. In comparison, GBP1 downregulation enhanced the accumulation of Brucella-induced reactive oxygen species (ROS) in macrophages. Overall, the data indicate a significant role of GBP1 in regulating brucellosis and suggest the function underlying its suppressive effect on the survival and growth of Brucella intracellularly.

Deciphering the Interrelationship of arnT Involved in Lipid-A Alteration with the Virulence of Salmonella Typhimurium.

The lipopolysaccharide (LPS) that resides on the outermost surface and protects Gram-negative bacteria from host defenses is one of the key components leading to Salmonella infection, particularly the endotoxic lipid A domain of LPS. Lipid A modifications have been associated with several genes such as the arnT that encodes 4-amino-4-deoxy-L-arabinose transferase, which can be critical for bacteria to resist cationic antimicrobial peptides and interfere with host immune recognition. However, the association of arnT with virulence is not completely understood. Thus, this study aimed to elucidate the interrelationship of the major lipid A modification gene arnT with Salmonella Typhimurium virulence. We observed that the arnT-deficient S. Typhimurium (JOL2943), compared to the wild type (JOL401), displayed a significant decrease in several virulence phenotypes such as polymyxin B resistance, intracellular survival, swarming, and biofilm and extracellular polymeric substance (EPS) production. Interestingly, the cell-surface hydrophobicity, adhesion, and invasion characteristics remained unaffected. Additionally, LPS isolated from the mutant induced notably lower levels of endotoxicity-related cytokines in RAW and Hela cells and mice, particularly IL-1ß with a nine-fold decrease, than WT. In terms of in vivo colonization, JOL2943 showed diminished presence in internal organs such as the spleen and liver by more than 60%, while ileal infectivity remained similar to JOL401. Overall, the arnT deletion rendered the strain less virulent, with low endotoxicity, maintained gut infectivity, and reduced colonization in internal organs. With these ideal characteristics, it can be further explored as a potential attenuated Salmonella strain for therapeutics or vaccine delivery systems.

Sneaky tactics: Ingenious immune evasion mechanisms of Bartonella.

Gram-negative Bartonella species are facultative intracellular bacteria that can survive in the harsh intracellular milieu of host cells. They have evolved strategies to evade detection and degradation by the host immune system, which ensures their proliferation in the host. Following infection, Bartonella alters the initial immunogenic surface-exposed proteins to evade immune recognition via antigen or phase variation. The diverse lipopolysaccharide structures of certain Bartonella species allow them to escape recognition by the host pattern recognition receptors. Additionally, the survival of mature erythrocytes and their resistance to lysosomal fusion further complicate the immune clearance of this species. Certain Bartonella species also evade immune attacks by producing biofilms and anti-inflammatory cytokines and decreasing endothelial cell apoptosis. Overall, these factors create a challenging landscape for the host immune system to rapidly and effectively eradicate the Bartonella species, thereby facilitating the persistence of Bartonella infections and creating a substantial obstacle for therapeutic interventions. This review focuses on the effects of three human-specific Bartonella species, particularly their mechanisms of host invasion and immune escape, to gain new perspectives in the development of effective diagnostic tools, prophylactic measures, and treatment options for Bartonella infections.

Comparative transcriptome analysis explored the molecular mechanisms of a luxR-type regulator regulating intracellular survival of Aeromonas hydrophila.

Aeromonas hydrophila is not a traditional intracellular bacterium. However, previous studies revealed that pathogenic A. hydrophila B11 could temporarily survive for at least 24 h in fish phagocytes, and the regulation of intracellular survival in bacteria was associated with regulators of the LuxR-type. The mechanisms of luxR08110 on the A. hydrophila's survival in macrophages were investigated using comprehensive transcriptome analysis and biological phenotype analysis in this study. The results showed that after luxR08110 was silenced, the intracellular survival ability of bacteria was significantly diminished. Comparative transcriptome analysis revealed that luxR08110 was a critical regulator of A. hydrophila, which regulated the expression of over 1200 genes, involving in bacterial flagellar assembly and chemotaxis, ribosome, sulphur metabolism, glycerolipid metabolism, and other mechanisms. Further studies confirmed that after the inhibition of expression of luxR08110, the motility, chemotaxis and adhesion of A. hydrophila significantly decreased. Moreover, compared with the wild-type strain, the survival rates of silencing strain were all considerably reduced under both H2O2 and low pH stress conditions. According to both transcriptome analysis and phenotypic tests, the luxR08110 of A. hydrophila could act as global regulator in bacteria intracellular survival. This regulator regulated intracellular survival of A. hydrophila mainly through two ways. One way is to regulate bacterial flagellar synthesis and further affects the motility, chemotaxis and adhesion of bacteria. The other way is to regulate sulphur and glycerolipid metabolisms, thus affecting bacterial energy production and the ability to resist environmental stress.

The Role of Rv1476 in Regulating Stress Response and Intracellular Survival of Mycobacterium tuberculosis.

The virulence of Mycobacterium tuberculosis (M. tuberculosis) is related to many factors, including intracellular survival, cell wall permeability, and cell envelope proteins. However, the biological function of the M. tuberculosis membrane protein Rv1476 remains unclear. To investigate the potential role played by Rv1476, we constructed an Rv1476 overexpression strain and found that overexpression of Rv1476 enhanced the intracellular survival of M. tuberculosis, while having no impact on the growth rate in vitro. Stress experiments demonstrated that the Rv1476 overexpression strain displayed increased susceptibility to different stresses compared to the wild-type strain. Transcriptome analysis showed that Rv1476 overexpression causes changes in the transcriptome of THP-1 cells, and differential genes are mainly enriched in cell proliferation, fatty acid degradation, cytokine-cytokine receptor interaction, and immune response pathways. Rv1476 overexpression inhibited the expression of some anti-tuberculosis-related genes, such as CCL1, IL15, IL16, ISG15, GBP5, IL23, ATG2A, IFNß, and CSF3. Altogether, we conclude that Rv1476 may play a critical role for M. tuberculosis in macrophage survival.

Metabolic diversity of human macrophages: potential influence on Staphylococcus aureus intracellular survival.

Staphylococcus aureus is a leading cause of medical device-associated biofilm infections. This is influenced by the ability of S. aureus biofilm to evade the host immune response, which is partially driven by the anti-inflammatory cytokine interleukin-10 (IL-10). Here, we show that treatment of human monocyte-derived macrophages (HMDMs) with IL-10 enhanced biofilm formation, suggesting that macrophage anti-inflammatory programming likely plays an important role during the transition from planktonic to biofilm growth. To identify S. aureus genes that were important for intracellular survival in HMDMs and how this was affected by IL-10, transposon sequencing was performed. The size of the S. aureus essential genome was similar between unstimulated HMDMs and the outgrowth control (18.5% vs 18.4%, respectively, with 54.4% overlap) but increased to 22.5% in IL-10-treated macrophages, suggesting that macrophage polarization status exerts differential pressure on S. aureus. Essential genes for S. aureus survival within IL-10-polarized HMDMs were dominated by negative regulatory pathways, including nitrogen and RNA metabolism, whereas S. aureus essential genes within untreated HMDMs were enriched in biosynthetic pathways such as purine and pyrimidine biosynthesis. To explore how IL-10 altered the macrophage intracellular metabolome, targeted metabolomics was performed on HMDMs from six individual donors. IL-10 treatment led to conserved alterations in distinct metabolites that were increased (dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, and acetyl-CoA) or reduced (fructose-6-phosphate, aspartic acid, and ornithine) across donors, whereas other metabolites were variable. Collectively, these findings highlight an important aspect of population-level heterogeneity in human macrophage responsiveness that should be considered when translating results to a patient population.IMPORTANCEOne mechanism that Staphylococcus aureus biofilm elicits in the host to facilitate infection persistence is the production of the anti-inflammatory cytokine interleukin-10 (IL-10). Here, we show that exposure of human monocyte-derived macrophages (HMDMs) to IL-10 promotes S. aureus biofilm formation and programs intracellular bacteria to favor catabolic pathways. Examination of intracellular metabolites in HMDMs revealed heterogeneity between donors that may explain the observed variability in essential genes for S. aureus survival based on nutrient availability for bacteria within the intracellular compartment. Collectively, these studies provide novel insights into how IL-10 polarization affects S. aureus intracellular survival in HMDMs and the importance of considering macrophage heterogeneity between human donors as a variable when examining effector mechanisms.

Mycoplasma invasion into host cells: An integrated model of infection strategy.

Mycoplasma belong to the genus Mollicutes and are notable for their small genome sizes (500-1300 kb) and limited biosynthetic capabilities. They exhibit pathogenicity by invading various cell types to survive as intracellular pathogens. Adhesion is a crucial prerequisite for successful invasion and is orchestrated by the interplay between mycoplasma surface adhesins and specific receptors on the host cell membrane. Invasion relies heavily on clathrin- and caveolae-mediated internalization, accompanied by multiple activated kinases, cytoskeletal rearrangement, and a myriad of morphological alterations, such as membrane invagination, nuclear hypertrophy and aggregation, cytoplasmic edema, and vacuolization. Once mycoplasma successfully invade host cells, they establish resilient sanctuaries in vesicles, cytoplasm, perinuclear regions, and the nucleus, wherein specific environmental conditions favor long-term survival. Although lysosomal degradation and autophagy can eliminate most invading mycoplasmas, some viable bacteria can be released into the extracellular environment via exocytosis, a crucial factor in the prolonging infection persistence. This review explores the intricate mechanisms by which mycoplasma invades host cells and perpetuates their elusive survival, with the aim of highlighting the challenge of eradicating this enigmatic bacterium.

Targeting Aminoglycoside Acetyltransferase Activity of Mycobacterium tuberculosis (H37Rv) Derived Eis (Enhanced Intracellular Survival) Protein with Quercetin.

Eis (Enhanced intracellular survival) protein is an aminoglycoside acetyltransferase enzyme classified under the family - GNAT (GCN5-related family of N-acetyltransferases) secreted by Mycobacterium tuberculosis (Mtb). The enzymatic activity of Eis results in the acetylation of kanamycin, thereby impairing the drug's action. In this study, we expressed and purified recombinant Eis (rEis) to determine the enzymatic activity of Eis and its potential inhibitor. Glide-enhanced precision docking was used to perform molecular docking with chosen ligands. Quercetin was found to interact Eis with a maximum binding affinity of -8.379 kcal/mol as compared to other ligands. Quercetin shows a specific interaction between the positively charged amino acid arginine in Eis and the aromatic ring of quercetin through π-cation interaction. Further, the effect of rEis was studied on the antibiotic activity of kanamycin A in the presence and absence of quercetin. It was observed that the activity of rEis aminoglycoside acetyltransferase decreased with increasing quercetin concentration. The results from the disk diffusion assay confirmed that increasing the concentration of quercetin inhibits the rEis protein activity. In conclusion, quercetin may act as a potential Eis inhibitor.

Bordetella pertussis targets the basolateral membrane of polarized respiratory epithelial cells, gets internalized, and survives in intracellular locations.

The airway epithelial barrier is a continuous highly organized cell layer that separates the exterior from the underlying mucosal tissue, preventing pathogen invasion. Several respiratory pathogens have evolved mechanisms to compromise this barrier, invade and even reside alive within the epithelium. Bordetella pertussis is a persistent pathogen that infects the human airway epithelium, causing whooping cough. Previous studies have shown that B. pertussis survives inside phagocytic and nonphagocytic cells, suggesting that there might be an intracellular stage involved in the bacterial infectious process and/or in the pathogen persistence inside the host. In this study we found evidence that B. pertussis is able to survive inside respiratory epithelial cells. According to our results, this pathogen preferentially attaches near or on top of the tight junctions in polarized human bronchial epithelial cells and disrupts these structures in an adenylate cyclase-dependent manner, exposing their basolateral membrane. We further found that the bacterial internalization is significantly higher in cells exposing this membrane compared with cells only exposing the apical membrane. Once internalized, B. pertussis mainly remains in nondegradative phagosomes with access to nutrients. Taken together, these results point at the respiratory epithelial cells as a potential niche of persistence.

Impact of MgtC on the Fitness of Yersinia pseudotuberculosis.

Yersinia pseudotuberculosis is an extracellular foodborne pathogen and usually causes self-limiting diarrhea in healthy humans. MgtC is known as a key subversion factor that contributes to intramacrophage adaptation and intracellular survival in certain important pathogens. Whether MgtC influences the fitness of Y. pseudotuberculosis is unclear. According to in silico analysis, MgtC in Y. pseudotuberculosis might share similar functions with other bacterial pathogens, such as Salmonella. Studies indicated that MgtC was clearly required for Y. pseudotuberculosis growth in vitro and bacterial survival in macrophages under Mg2+ starvation. Transcriptome analysis by RNA-seq indicated that 127 differentially expressed genes (DEGs) (fold change > 2 and p < 0.001) were discovered between wild-type PB1+ and mgtC mutant inside macrophages. However, a lack of MgtC only moderately, albeit significantly, reduced the virulence of Y. pseudotuberculosis in mice. Overall, this study provides additional insights for the role of MgtC in Y. pseudotuberculosis.

Mycobacterium tuberculosis Fatty Acyl-CoA Synthetase fadD33 Promotes Bacillus Calmette-Guérin Survival in Hostile Extracellular and Intracellular Microenvironments in the Host.

Tuberculosis, caused by Mycobacterium tuberculosis (M. tb), remains a significant global health challenge. The survival of M. tb in hostile extracellular and intracellular microenvironments is crucial for its pathogenicity. In this study, we discovered a Bacillus Calmette-Guérin (BCG) mutant B1033 that potentially affected mycobacterium pathogenicity. This mutant contained an insertion mutation gene, fadD33, which is involved in lipid metabolism; however, its direct role in regulating M. tb infection is not well understood. Here, we found that the absence of fadD33 reduced BCG adhesion and invasion into human pulmonary alveolar epithelial cells and increased the permeability of the mycobacterial cell wall, allowing M. tb to survive in the low pH and membrane pressure extracellular microenvironment of the host cells. The absence of fadD33 also inhibited the survival of BCG in macrophages by promoting the release of proinflammatory cytokines, such as interleukin (IL)-1ß, IL-6, and tumors necrosis factor-α, through the mitogen-activated protein kinase p38 signaling pathway. Overall, these findings provide new insights into M. tb mechanisms to evade host defenses and might contribute to identifying potential therapeutic and vaccine targets for tuberculosis prevention.

The PPE2 protein of Mycobacterium tuberculosis is secreted during infection and facilitates mycobacterial survival inside the host.

Mycobacterium tuberculosis secrets various effector proteins to evade host immune responses for facilitating its intracellular survival. The bacterial genome encodes several unique PE/PPE family proteins, which have been implicated to play important role in mycobacterial pathogenesis. A member of this family, PPE2 have been shown to contain a monopartite nuclear localization signal (NLS) and a DNA binding domain. In this study, we demonstrate that PPE2 protein is present in the sera of mice infected with either M. smegmatis expressing PPE2 or a clinical strain of M. tuberculosis (CDC1551). It was found that exogenously added PPE2 can permeate through the macrophage cell membrane and eventually translocate into the nucleus which requires the presence of NLS which showed considerable homology to HIV-tat like cell permeable peptides. Exogenously added PPE2 could inhibit NO production and decreased mycobacterial survival in macrophages. PPE2-null mutant of M. tuberculosis failed to inhibit NO production and had poor survival in macrophages which could be rescued by complementation with full-length PPE2. PPE2-null mutants also had poor survival in the lungs of infected mice indicating that PPE2 even when present in the bloodstream can confer a survival advantage to mycobacteria.

Mycobacterium tuberculosis suppresses host DNA repair to boost its intracellular survival.

Mycobacterium tuberculosis (Mtb) triggers distinct changes in macrophages, resulting in the formation of lipid droplets that serve as a nutrient source. We discover that Mtb promotes lipid droplets by inhibiting DNA repair responses, resulting in the activation of the type-I IFN pathway and scavenger receptor-A1 (SR-A1)-mediated lipid droplet formation. Bacterial urease C (UreC, Rv1850) inhibits host DNA repair by interacting with RuvB-like protein 2 (RUVBL2) and impeding the formation of the RUVBL1-RUVBL2-RAD51 DNA repair complex. The suppression of this repair pathway increases the abundance of micronuclei that trigger the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway and subsequent interferon-ß (IFN-ß) production. UreC-mediated activation of the IFN-ß pathway upregulates the expression of SR-A1 to form lipid droplets that facilitate Mtb replication. UreC inhibition via a urease inhibitor impaired Mtb growth within macrophages and in vivo. Thus, our findings identify mechanisms by which Mtb triggers a cascade of cellular events that establish a nutrient-rich replicative niche.