Mycobacterium avium MAV_2941 mimics phosphoinositol-3-kinase to interfere with macrophage phagosome maturation

Advancements in dual-target inhibitors of PI3K for tumor therapy: Clinical progress, development strategies, prospects

Phosphoinositide 3-kinases (PI3Ks) modify lipids by the phosphorylation of inositol phospholipids at the 3'-OH position, thereby participating in signal transduction and exerting effects on various physiological processes such as cell growth, metabolism, and organism development. PI3K activation also drives cancer cell growth, survival, and metabolism, with genetic dysregulation of this pathway observed in diverse human cancers. Therefore, this target is considered a promising potential therapeutic target for various types of cancer. Currently, several selective PI3K inhibitors and one dual-target PI3K inhibitor have been approved and launched on the market. However, the majority of these inhibitors have faced revocation or voluntary withdrawal of indications due to concerns regarding their adverse effects. This article provides a comprehensive review of the structure and biological functions, and clinical status of PI3K inhibitors, with a specific emphasis on the development strategies and structure-activity relationships of dual-target PI3K inhibitors. The findings offer valuable insights and future directions for the development of highly promising dual-target drugs targeting PI3K.

MptpB Inhibitor Improves the Action of Antibiotics against Mycobacterium tuberculosis and Nontuberculous Mycobacterium avium Infections

Treatment of Mycobacterium tuberculosis and Mycobacterium avium infections requires multiple drugs for long time periods. Mycobacterium protein-tyrosine-phosphatase B (MptpB) is a key M. tuberculosis virulence factor that subverts host antimicrobial activity to promote intracellular survival. Inhibition of MptpB reduces the infection burden in vivo and offers new opportunities to improve current treatments. Here, we demonstrate that M. avium produces an MptpB orthologue and that the MptpB inhibitor C13 reduces the M. avium infection burden in macrophages. Combining C13 with the antibiotics rifampicin or bedaquiline showed an additive effect, reducing intracellular infection of both M. tuberculosis and M. avium by 50%, compared to monotreatment with antibiotics alone. This additive effect was not observed with pretomanid. Combining C13 with the minor groove-binding compounds S-MGB-362 and S-MGB-363 also reduced the M. tuberculosis intracellular burden. Similar additive effects of C13 and antibiotics were confirmed in vivo using Galleria mellonella infections. We demonstrate that the reduced mycobacterial burden in macrophages observed with C13 treatments is due to the increased trafficking to lysosomes.

Apoptosis Inhibitor of Macrophages Contributes to the Chronicity of Mycobacterium avium Infection by Promoting Foamy Macrophage Formation

In Mycobacterium avium infections, macrophages play a critical role in the host defense response. Apoptosis inhibitor of macrophage (AIM), also known as CD5L, may represent a novel supportive therapy against various diseases, including metabolic syndrome and infectious diseases. The mechanisms of AIM include modulating lipid metabolism in macrophages and other host cells. We investigated the role of AIM in M. avium infections in vitro and in vivo. In a mouse model of M. avium pneumonia, foamy macrophages were induced 6 wk after infection. The bacteria localized in these macrophages. Flow cytometric analysis also confirmed that the percentage of CD11chighMHCclassIIhigh interstitial and alveolar macrophages, a cell surface marker defined as foamy macrophages, increased significantly after infection. AIM in alveolar lavage fluid and serum gradually increased after infection. Administration of recombinant AIM significantly increased the number of bacteria in the lungs of mice, accompanied by the induction of inflammatory cytokine and iNOS expression. In mouse bone marrow-derived macrophages, the mRNA expression of AIM after M. avium infection and the amount of AIM in the supernatant increased prior to the increase in intracellular bacteria. Infected cells treated with anti-AIM Abs had fewer bacteria and a higher percentage of apoptosis-positive cells than infected cells treated with isotype control Abs. Finally, AIM in the sera of patients with M. avium-pulmonary disease was measured and was significantly higher than in healthy volunteers. This suggests that AIM production is enhanced in M. avium-infected macrophages, increasing macrophage resistance to apoptosis and providing a possible site for bacterial growth.

Zooming in on common immune evasion mechanisms of pathogens in phagolysosomes: potential broad-spectrum therapeutic targets against infectious diseases

The intracellular viral, bacterial, or parasitic pathogens evade the host immune challenges to propagate and cause fatal diseases. The microbes overpower host immunity at various levels including during entry into host cells, phagosome formation, phagosome maturation, phagosome-lysosome fusion forming phagolysosomes, acidification of phagolysosomes, and at times after escape into the cytosol. Phagolysosome is the final organelle in the phagocyte with sophisticated mechanisms to degrade the pathogens. The immune evasion strategies by the pathogens include the arrest of host cell apoptosis, decrease in reactive oxygen species, the elevation of Th2 anti-inflammatory response, avoidance of autophagy and antigen cross-presentation pathways, and escape from phagolysosomal killing. Since the phagolysosome organelle in relation to infection/cure is seldom discussed in the literature, we summarize here the common host as well as pathogen targets manipulated or utilized by the pathogens established in phagosomes and phagolysosomes, to hijack the host immune system for their benefit. These common molecules or pathways can be broad-spectrum therapeutic targets for drug development for intervention against infectious diseases caused by different intracellular pathogens.

Modulating macrophage function to reinforce host innate resistance against Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) is the main causative agent of infectious diseases in humans among nontuberculous mycobacteria (NTM) that are ubiquitous organisms found in environmental media such as soil as well as in domestic and natural waters. MAC is a primary causative agent of NTM-lung disease that threaten immunocompromised or structural lung disease patients. The incidence and the prevalence of M. tuberculosis infection have been reduced, while MAC infections and mortality rates have increased, making it a cause of global health concern. The emergence of drug resistance and the side effects of long-term drug use have led to a poor outcome of treatment regimens against MAC infections. Therefore, the development of host-directed therapy (HDT) has recently gained interest, aiming to accelerate mycobacterial clearance and reversing lung damage by employing the immune system using a novel adjuvant strategy to improve the clinical outcome of MAC infection. Therefore, in this review, we discuss the innate immune responses that contribute to MAC infection focusing on macrophages, chief innate immune cells, and host susceptibility factors in patients. We also discuss potential HDTs that can act on the signaling pathway of macrophages, thereby contributing to antimycobacterial activity as a part of the innate immune response during MAC infection. Furthermore, this review provides new insights into MAC infection control that modulates and enhances macrophage function, promoting host antimicrobial activity in response to potential HDTs and thus presenting a deeper understanding of the interactions between macrophages and MACs during infection.

Mycobacterium avium Subsp. hominissuis Interactions with Macrophage Killing Mechanisms

Non-tuberculosis mycobacteria (NTM) are ubiquitously found throughout the environment. NTM can cause respiratory infections in individuals with underlying lung conditions when inhaled, or systemic infections when ingested by patients with impaired immune systems. Current therapies can be ineffective at treating NTM respiratory infections, even after a long course or with multidrug treatment regimens. NTM, such as Mycobacterium avium subspecies hominissuis (M. avium), is an opportunistic pathogen that shares environments with ubiquitous free-living amoeba and other environmental hosts, possibly their evolutionary hosts. It is highly likely that interactions between M. avium and free-living amoeba have provided selective pressure on the bacteria to acquire survival mechanisms, which are also used against predation by macrophages. In macrophages, M. avium resides inside phagosomes and has been shown to exit it to infect other cells. M. avium's adaptation to the hostile intra-phagosomal environment is due to many virulence mechanisms. M. avium is able to switch the phenotype of the macrophage to be anti-inflammatory (M2). Here, we have focused on and discussed the bacterial defense mechanisms associated with the intra-phagosome phase of infection. M. avium possesses a plethora of antioxidant enzymes, including the superoxide dismutases, catalase and alkyl hydroperoxide reductase. When these defenses fail or are overtaken by robust oxidative burst, many other enzymes exist to repair damage incurred on M. avium proteins, including thioredoxin/thioredoxin reductase. Finally, M. avium has several oxidant sensors that induce transcription of antioxidant enzymes, oxidation repair enzymes and biofilm- promoting genes. These expressions induce physiological changes that allow M. avium to survive in the face of leukocyte-generated oxidative stress. We will discuss the strategies used by M. avium to infect human macrophages that evolved during its evolution from free-living amoeba. The more insight we gain about M. avium's mode of pathogenicity, the more targets we can have to direct new anti-virulence therapies toward.

Macrophage Proteome Analysis at Different Stages of Mycobacterium avium Subspecies paratuberculosis Infection Reveals a Mechanism of Pathogen Dissemination

Johne’s disease is a chronic and usually fatal enteric infection of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP) and is responsible for hundreds of millions of dollars in losses for the agricultural industry. Natural infection typically begins with bacterial uptake and translocation through the epithelium of the small intestine, followed by ingestion by tissue macrophages and dissemination via the lymphatic or blood system throughout the body. To gain insights into the host responses and adaptation of MAP within phagocytic cells, we utilized the previously developed cell culture passage model, and mass spectrometric-based quantitative proteomic approach. Using the cell culture system, which mimics an in vivo interaction of MAP with intestinal epithelium and tissue macrophages, bacteria were passed through the bovine epithelial cells and, subsequently, used for macrophage infection (termed indirect infection), while uninfected cells and macrophage infection initiated with the culture grown bacteria (termed direct infection) served as controls. Approximately 3900 proteins were identified across all studied groups. The comparison within the subset of proteins that showed synthesis for more than two-fold in the direct infection over the uninfected control revealed an enrichment for the pro-inflammatory pathways such as the NF-κB and cytokine/chemokine signaling, positive regulation of defense response, cell activation involved in the immune response and adaptive immune system. While these responses were absent in the indirect infection, cellular pathways such as cell cycle, healing, regulation of cell adhesion, ensemble of core extracellular matrix proteins, cell surface integrins and proteins mediating the integrin signaling were remarkably high within the indirect infection. In addition to global analysis of the macrophage proteome, we further validated the proteomics data and confirmed that MAP passage through epithelial cells modulates the expression and signaling of integrins in phagocytes. In this study, we demonstrate that predominant expression of integrins in the indirectly infected macrophages allows phagocytic cells to initiate stronger binding and efficient translocation through the endothelial cells, suggesting the important role of integrins in the spread of MAP infection.

Genetic Involvement of Mycobacterium avium Complex in the Regulation and Manipulation of Innate Immune Functions of Host Cells

Mycobacterium avium complex (MAC), a collection of mycobacterial species representing nontuberculous mycobacteria, are characterized as ubiquitous and opportunistic pathogens. The incidence and prevalence of infectious diseases caused by MAC have been emerging globally due to complications in the treatment of MAC-pulmonary disease (PD) in humans and the lack of understating individual differences in genetic traits and pathogenesis of MAC species or subspecies. Despite genetically close one to another, mycobacteria species belonging to the MAC cause diseases to different host range along with a distinct spectrum of disease. In addition, unlike Mycobacterium tuberculosis, the underlying mechanisms for the pathogenesis of MAC infection from environmental sources of infection to their survival strategies within host cells have not been fully elucidated. In this review, we highlight unique genetic and genotypic differences in MAC species and the virulence factors conferring the ability to MAC for the tactics evading innate immune attacks of host cells based on the recent advances in genetic analysis by exemplifying M. avium subsp. hominissuis, a major representative pathogen causing MAC-PD in humans. Further understanding of the genetic link between host and MAC may contribute to enhance host anti-MAC immunity, but also provide novel therapeutic approaches targeting the pangenesis-associated genes of MAC.

Exposure of Mycobacterium avium subsp. homonissuis to Metal Concentrations of the Phagosome Environment Enhances the Selection of Persistent Subpopulation to Antibiotic Treatment

Mycobacterium avium subspecies hominissuis (MAH) is an opportunistic intracellular pathogen causing infections in individuals with chronic lung conditions and patients with immune-deficient disorders. The treatment of MAH infections is prolonged and outcomes many times are suboptimal. The reason for the extended treatment is complex and reflects the inability of current antimicrobials to clear diverse phenotypes of MAH quickly, particularly, the subpopulation of susceptible but drug-tolerant bacilli where the persistent fitness to anti-MAH drugs is stimulated and enhanced by the host environmental stresses. In order to enhance the pathogen killing, we need to understand the fundamentals of persistence mechanism and conditions that can initiate the drug-tolerance phenotype in mycobacteria. MAH can influence the intracellular environment through manipulation of the metal concentrations in the phagosome of infected macrophages. While metals play important role and are crucial for many cellular functions, little is known how vacuole elements influence persistence state of MAH during intracellular growth. In this study, we utilized the in vitro model mimicking the metal concentrations and pH of MAH phagosome at 1 h and 24 h post-infection to distinguish if metals encountered in phagosome could act as a trigger factor for persistence phenotype. Antibiotic treatment of metal mix exposed MAH demonstrates that metals of the phagosome environment can enhance the persistence state, and greater number of tolerant bacteria is recovered from the 24 h metal mix when compared to the viable pathogen number in the 1 h metal mix and 7H9 growth control. In addition, bacterial phenotype induced by the 24 h metal mix increases MAH tolerance to macrophage killing in TNF-α and IFN-γ activated cells, confirming presence of persistent MAH in the 24 h metal mix condition. This work shows that the phagosome environment can promote persistence population in MAH, and that the population differs dependent on a concentration of metals.

Survival of Lawsonia intracellularis in porcine peripheral blood monocyte-derived macrophages

Lawsonia intracellularis, an obligately intracellular enteric bacterium, infects intestinal epithelial cells, but may also be found within macrophages in the intestinal lamina propria of affected pigs. Macrophages play an important role in host defense against infectious agents, but the role of this cell in L. intracellularis infection is not well understood. The aim of this study was to evaluate the permissibility of macrophages to L. intracellularis infection in vitro. Pure culture of L. intracellularis was added to swine peripheral blood monocyte-derived macrophages. Viability of intracytoplasmic L. intracellularis was evaluated at different time points by transmission electron microscopy (TEM). Potential replication of L. intracellularis in macrophages was also evaluated by qPCR. By TEM, phagocytosis L. intracellularis within of phagolysosomes were observed 1-hour post-infection (hpi) and bacterial structures in binary fission at 48 hpi. The number of intracellular bacteria was determined at 1, 4, 24, 48, and 72 hpi by qPCR in infected macrophages and compared to the number of intracellular bacteria from culture in McCoy cells. In both cell lines, the amount of L. intracellularis was decreased at 4 hpiand increased at 24 hpi. The number of intracellular bacteria continued to increase in McCoy cells over time. This is the first study showing interaction, survival and propagation of L. intracellularis in macrophages. These findings are critical to establish an experimental model for future studies of the pathogenesis of porcine proliferative enteropathy and the potential persistence of L. intracellularis in macrophages during chronic infections.

Nontuberculous Mycobacteria Persistence in a Cell Model Mimicking Alveolar Macrophages

Nontuberculous Mycobacteria (NTM) respiratory infections have been gradually increasing. Here, THP-1 cells were used as a model to evaluate intracellular persistence of three NTM species (reference and clinical strains) in human alveolar macrophages. The contribution of phagosome acidification, nitric oxide (NO) production and cell dead on NTM intracellular fate was assessed. In addition, strains were characterized regarding their repertoire of virulence factors by whole-genome sequencing. NTM experienced different intracellular fates: M. smegmatis and M. fortuitum ATCC 6841 were cleared within 24h. In contrast, M. avium strains (reference/clinical) and M. fortuitum clinical strain were able to replicate. Despite this fact, unexpectedly high percentages of acidified phagosomes were found harbouring rab7, but not CD63. All NTM were able to survive in vitro at acidic pHs, with the exception of M. smegmatis. Our data further suggested a minor role for NO in intracellular persistence and that apoptosis mediated by caspase 8 and 3/7, but not necrosis, is triggered during NTM infection. Insights regarding the bacteria genomic backbone corroborated the virulence potential of M. avium and M. fortuitum. In conclusion, the phenotypic traits detected contrast with those described for M. tuberculosis, pointing out that NTM adopt distinct strategies to manipulate the host immune defense and persist intracellularly.

Mycobacterium avium subsp. hominissuis effector MAVA5_06970 promotes rapid apoptosis in secondary-infected macrophages during cell-to-cell spread

Mycobacterium avium subsp. hominissuis is an opportunistic intracellular pathogen associated with disease in patients either immunosuppression or chronic lung pathology. Once in the host, M. avium preferentially infects and replicates within the phagocytic cells. The host driven macrophage apoptosis appears to be an essential aspect of innate immunity during bacterial infection; however, the existing evidence suggests that M. avium has evolved adaptive approaches to trigger the phagocyte apoptosis, exit apoptotic cells or via ingestion of infected apoptotic bodies subsequently infect neighboring macrophages. By evaluating 4,000 transposon mutants of M. avium in THP-1 cells, we identified clones that can trigger a new form of early host cell apoptosis, which is only observed upon entry into the “secondary-infected” macrophages. Inactivation of MAVA5_06970 gene lead to significant attenuation in intracellular growth within macrophages and mice, and impaired M. avium to induce rapid apoptosis in the “secondary-infected” cells as measured by Annexin V-FITC detection assay. Complementation of MAVA5_06970 gene corrected the attenuation as well as apoptotic phenotypes. The MAVA5_06970 gene encodes for a secreted protein. Using the pull-down assay and then confirmed with the yeast two-hybrid screen, we found that MAVA5_06970 effector interacts with the Secreted Phosphoprotein 1, the cytokine also known as Osteopontin. This interaction enhances the THP-1 cell apoptosis and, consequently, restricts the production of interleukin-12 that likely may limit the activation of the type I immunity pathway in vivo. This work identified a key virulence effector of M. avium that contributes to the cell-to-cell spread of the pathogen.

JVA, an isoniazid analogue, is a bioactive compound against a clinical isolate of the Mycobacterium avium complex

Bacteria belonging to Mycobacterium avium complex are organisms of low pathogenicity that infect immunosuppressed individuals. Infection is treated with an antimicrobial macrolide, Clarithromycin (CAM) or Azitromycin, associated with Ethambutol and Rifabutin during 12 months. Regimen long duration and side effects hinder patient's commitment to treatment favoring emergence of antibiotic resistance. In this present study, we evaluated the activity of JVA, an Isoniazid (INH) derivative, against M. avium 2447, a clinical isolate. We demonstrated that JVA reduces M. avium 2447 growth in macrophages, more efficiently than CAM and INH. In order to explore JVA mechanism of action, we investigated compound properties and performed pH-dependent stability studies. Our results suggest an enhanced ability of JVA to cross biological membranes. Furthermore, we suggest that in acidic conditions of macrophages' phagosomes, where mycobacteria replicate, JVA would be promptly hydrolyzed to INH, delivering the adduct INH-nicotinamide adenine dinucleotide and thus inhibiting M. avium 2447 growth.

Characterization of membrane vesicles released by Mycobacterium avium in response to environment mimicking the macrophage phagosome

Aim:

To investigate the formation of Mycobacterium avium membrane vesicles (MVs) within macrophage phagosomes.

Materials & methods:

A phagosome model was utilized to characterize proteomics and lipidomics of MVs. A click chemistry-based enrichment assay was employed to examine the presence of MV proteins in the cytosol of host cells.

Results:

Exposure to metals at concentrations present in phagosomes triggers formation of bacterial MVs. Proteomics identified several virulence factors, including enzymes involved in the cell wall synthesis, lipid and fatty acid metabolism. Some of MV proteins were also identified in the cytosol of infected macrophages. MVs harbor dsDNA.

Conclusion:

M. avium produces MVs within phagosomes. MVs carry products with potential roles in modulation of host immune defenses and intracellular survival.

Identification of Carassius auratus gibelio liver cell proteins interacting with the GABAA receptor γ2 subunit using a yeast two-hybrid system

The γ-aminobutyric acid type A (GABA_A) receptor is an important pentameric inhibitory neurotransmitter receptor, and the γ2 subunit of this receptor plays a key role in potentiation of the GABA_A response. We previously detected that the expression of GABA_A receptor in the livers of Carassius auratus gibelio significantly increased after medication (avermectin and difloxacin treatment). In order to better understand the mechanism of action of the GABA_A receptor γ2 subunit in the livers of C. auratus gibelio, we constructed a C. auratus gibelio liver cDNA library (the titer value of 1.2 × 10⁶ cfu/mL) and identified the proteins that interact with the GABA_A receptor γ2 subunit by using a yeast two-hybrid assay. The yeast two-hybrid screening yielded seven positive clones, namely, prelid3b, cdc42, sgk1, spg21, proteasome, chia.5, and AP-3 complex subunit beta-1, all of which have been annotated by the NCBI database. The functions of these proteins are complex; therefore, additional studies are required to determine the specific interactions of these proteins with the GABA_A receptor γ2 subunit in the liver of C. auratus gibelio. Although the interactions identified by the yeast two-hybrid system should be considered as preliminary results, the findings of this study may provide further direction and a foundation for future research focusing on the mechanisms of the GABA_A receptor γ2 subunit in C. auratus gibelio livers.

Persistent mycobacteria evade an antibacterial program mediated by phagolysosomal TLR7/8/MyD88 in human primary macrophages

Pathogenic mycobacteria reside in macrophages where they avoid lysosomal targeting and degradation through poorly understood mechanisms proposed to involve arrest of phagosomal maturation at an early endosomal stage. A clear understanding of how this relates to host defenses elicited from various intracellular compartments is also missing and can only be studied using techniques allowing single cell and subcellular analyses. Using confocal imaging of human primary macrophages infected with Mycobacterium avium (Mav) we show evidence that Mav phagosomes are not arrested at an early endosomal stage, but mature to a (LAMP1⁺/LAMP2⁺/CD63⁺) late endosomal/phagolysosomal stage where inflammatory signaling and Mav growth restriction is initiated through a mechanism involving Toll-like receptors (TLR) 7 and 8, the adaptor MyD88 and transcription factors NF-κB and IRF-1. Furthermore, a fraction of the mycobacteria re-establish in a less hostile compartment (LAMP1^-/LAMP2^-/CD63^-) where they not only evade destruction, but also recognition by TLRs, growth restriction and inflammatory host responses that could be detrimental for intracellular survival and establishment of chronic infections.

Mycobacterium avium is increasingly reported as a causative agent of non-tuberculous disease in immunocompromised patients and in individuals with underlying disease or using immunosuppressant drugs, with prevalence often higher than the more pathogenic M. tuberculosis in developed countries. Both M. avium and M. tuberculosis cause persistent infections by surviving inside host macrophages. Here, we identify from which compartment M. avium evoke inflammatory signaling in human primary macrophages, and the pattern-recognition receptors involved. In essence, we present three key findings: 1) M. avium phagosomes are not arrested at an early endosomal stage, but rather mature normally into phagolysosomes from where a fraction of the bacteria escape and re-establish in a new compartment. 2) In addition to avoiding degradation in phagolysosomes, by escaping M. avium also evade inflammatory signaling. 3) M. avium unable to escape is degraded in phagolysosomes and recognized by Toll-like receptors 7 and 8. Our results can contribute to new understanding of intracellular infections, and thus have vital clinical implications for development of novel anti-microbial strategies and host-targeted therapy to mycobacterial and other infectious diseases.

The Voltage-Dependent Anion Channels (VDAC) of Mycobacterium avium phagosome are associated with bacterial survival and lipid export in macrophages

Mycobacterium avium subsp. hominissuis is associated with infection of immunocompromised individuals as well as patients with chronic lung disease. M. avium infects macrophages and actively interfere with the host killing machinery such as apoptosis and autophagy. Bacteria alter the normal endosomal trafficking, prevent the maturation of phagosomes and modify many signaling pathways inside of the macrophage by secreting effector molecules into the cytoplasm. To investigate whether M. avium needs to attach to the internal surface of the vacuole membrane before releasing efferent molecules, vacuole membrane proteins were purified and binding to the surface molecules present in intracellular bacteria was evaluated. The voltage-dependent anion channels (VDAC) were identified as components of M. avium vacuoles in macrophages. M. avium mmpL4 proteins were found to bind to VDAC-1 protein. The inactivation of VDAC-1 function either by pharmacological means or siRNA lead to significant decrease of M. avium survival. Although, we could not establish a role of VDAC channels in the transport of known secreted M. avium proteins, we demonstrated that the porin channels are associated with the export of bacterial cell wall lipids outside of vacuole. Suppression of the host phagosomal transport systems and the pathogen transporter may serve as therapeutic targets for infectious diseases.

Comparative analysis of the genomes of clinical isolates of Mycobacterium avium subsp. hominissuis regarding virulence-related genes

PURPOSE

Mycobacterium avium subsp. hominissuis is a member of the M. avium complex, a heterogeneous group of bacteria that cause lung infection in immunocompetent patients or disseminated infection in patients with immunosuppression. The bacteria belonging to this complex have variable virulence, depending on the strain considered, and therefore a representative of the most common clinical phenotype was analysed.

METHODOLOGY

The genomic sequences of four M. avium subsp. hominissuis isolates obtained from clinical specimens were completed. Mav101, Mav100 and MavA5 were isolated from the blood of patients with AIDS. MavA5 was disseminated from the lung, while Mav3388 was isolated from the lungs of a patient with chronic lung disease. The sequences were annotated using the published Mav104 genome as a blueprint. Functional and virulence analyses of the sequences were carried out. Mice studies comparing the virulence of the strains were performed.

RESULTS

Findings showed that while Mav101 was very similar to Mav104, there were numerous differences between Mav104 and the remaining strains at nucleotide and predicted protein levels. The presence of genes associated with biofilm formation and several known virulence-related genes were sometimes differentially present among the isolates, suggesting overlapping functions by different genetic determinants.

CONCLUSIONS

The sequences provided important information about M. avium heterogenicity and evolution as a pathogen. The limitation is the lack of understanding on possible overlapping functions of genes/proteins.

Molecular basis of mycobacterial survival in macrophages

Macrophages play an essential role in the immune system by ingesting and degrading invading pathogens, initiating an inflammatory response and instructing adaptive immune cells, and resolving inflammation to restore homeostasis. More interesting is the fact that some bacteria have evolved to use macrophages as a natural habitat and tools of spread in the host, e.g., Mycobacterium tuberculosis (Mtb) and some non-tuberculous mycobacteria (NTM). Mtb is considered one of humanity's most successful pathogens and is the causal agent of tuberculosis, while NTMs cause opportunistic infections all of which are of significant public health concern. Here, we describe mechanisms by which intracellular pathogens, with an emphasis on mycobacteria, manipulate macrophage functions to circumvent killing and live inside these cells even under considerable immunological pressure. Such macrophage functions include the selective evasion or engagement of pattern recognition receptors, production of cytokines, reactive oxygen and nitrogen species, phagosome maturation, as well as other killing mechanisms like autophagy and cell death. A clear understanding of host responses elicited by a specific pathogen and strategies employed by the microbe to evade or exploit these is of significant importance for the development of effective vaccines and targeted immunotherapy against persistent intracellular infections like tuberculosis.

Identification of Mycobacterium avium subsp. hominissuis secreted proteins using an in vitro system mimicking the phagosomal environment

Background

Mycobacterium avium subsp. hominissuis is a common intracellular pathogen that infects patients with HIV/AIDS and cause lung infection in patients with underlying lung pathology. M.avium preferably infects macrophages and uses diverse mechanisms to alter phagosome maturation. Once in the macrophage, the pathogen can alter the host cellular defenses by secreting proteins into the cytosol of host cells, but despite considerable research, only a few secreted effector proteins have been identified. We hypothesized that the environmental cues inside the phagosome can trigger bacterial protein secretion. To identify M. avium secretome within the phagosome, we utilized a previously established in vitro system that mimics the metal ion concentrations and pH of the M. avium phagosome.

Results

M. avium was exposed to phagosome metal concentrations for different time points and exported proteins were profiled and analyzed against bacterial proteins secreted in the culture medium. Mass spectrometric analysis of the secreted proteome identified several proteins, of which 46 were unique to bacteria incubated in the metal mixture. Ten of potential effectors were selected and secretion of these proteins was monitored within M. avium infected mononuclear phagocytic cells using the beta-lactamase FRET-based reporter system. In addition, pull-down assay was performed for secreted calmodulin-like protein MAV_1356 protein to evaluate for eukaryotic target. All examined M. avium proteins were secreted into the macrophage cytosol, and gene expression analysis suggested that the metal environment likely stimulates secretion of pre-made proteins. Further investigation of bacterial secreted MAV_1356 protein, lead to the observation that the MAV_1356 interacts with the host proteins Annexin A1 and Protein S100-A8.

Conclusions

We established an in vitro system for the study if proteins secreted intracellularly, and revealed that the metal mixture mimicking the concentration of metals in the phagosome environment, triggers protein secretion.