Invasion of the brain and chronic central nervous system infection after systemic Mycobacterium avium complex infection in mice

Central nervous system mycobacteriosis caused by Mycobacterium genavense in degus (Octodon degus)

Degus (Octodon degus) that were kept at a breeding facility presented with neurological or respiratory symptoms and died. Necropsies were performed on 9 individuals, and no significant gross lesions were found. Histologically, spinal cord necrosis was observed in all 9 cases and granulomatous myelitis in 5 of the 9 cases. Locally extensive necrosis of the brain and encephalitis were observed in 7 of the 9 cases. Acid-fast bacteria were found in the spinal cords, brains, and lungs from all 9 cases. Immunohistochemically, Mycobacterium tuberculosis antigen was observed in the spinal cords, brains, and lungs from all 9 cases. Double-labeling immunofluorescence revealed M. tuberculosis antigen in IBA1- and myeloperoxidase-immunopositive cells. Extracted genomic DNA from 8 of the 9 cases was successfully amplified with the primers for Mycobacterium genavense ITS1 and hypothetical 21 kDa protein genes, and the polymerase chain reaction products were identified as M. genavense by DNA sequencing. This report highlights the susceptibility of degus to M. genavense infection in the central nervous system.

Nanoparticle delivery through the BBB in central nervous system tuberculosis

Recent advances in Nanotechnology have revolutionized the production of materials for biomedical applications. Nowadays, there is a plethora of nanomaterials with potential for use towards improvement of human health. On the other hand, very little is known about how these materials interact with biological systems, especially at the nanoscale level, mainly because of the lack of specific methods to probe these interactions. In this review, we will analytically describe the journey of nanoparticles (NPs) through the brain, starting from the very first moment upon injection. We will preliminarily provide a brief overlook of the physicochemical properties of NPs. Then, we will discuss how these NPs interact with the body compartments and biological barriers, before reaching the blood-brain barrier (BBB), the last gate guarding the brain. Particular attention will be paid to the interaction with the biomolecular, the bio-mesoscopic, the (blood) cellular, and the tissue barriers, with a focus on the BBB. This will be framed in the context of brain infections, especially considering central nervous system tuberculosis (CNS-TB), which is one of the most devastating forms of human mycobacterial infections. The final aim of this review is not a collection, nor a list, of current literature data, as it provides the readers with the analytical tools and guidelines for the design of effective and rational NPs for delivery in the infected brain.

Etiological and Radiological Spectrum of Longitudinal Myelitis: A Hospital-Based Study in North East India

Introduction  An inflammatory lesion of the spinal cord where three or more than three vertebral segments of the cord is involved is called longitudinal extensive myelitis (LETM). It has several varied causes out of which neuromyelitis optica (NMO) and its spectrum disorder have received a distinct entity. Various radiological and clinical features help us to suspect an etiology which then further guides us into the treatment protocol and prognosis of the patients.

Materials and Methods  A retrospective study performed in a referral center in North East India in 15 months. Thirty-two patients of LETM were enrolled based on clinical and radiological available data. An attempt was made to classify the various etiologies and correlate with their radiological findings.

Results  The most common etiology noted was NMO seen in 7 patients (21.8%) followed by tuberculosis (TB) (18.7%) and post-infection myelitis (18.7%). Other etiology seen was acute disseminated encephalomyelitis (6.24%), spinal cord infarct (3.12%), radiation myelitis (6.24%), Japanese encephalitis sequalae (3.12%), systemic lupus erythematosus (3.12%), and remained undiagnosed in six patients (18.7%). Radiologically, cervico-dorsal spine was most common location in NMO (71%) whereas dorsolumbar in TB (50%). The lesion was predominantly central in both NMO (100%) and TB (80%) as compared with the other causes of LETM. It was noted that more than 50% of the transverse area of the cord was involved in both NMO (71%) and TB (50%), but < 50% involvement were more common in the post-infectious and others causes of LETM.

Conclusion  LETM has a various differential diagnosis, infection need to be kept in mind while ruling out NMO. Radiological features can suggest or help differentiate the various etiologies of LETM but NMO and infection like TB almost has the same features except for a different cord site predilection.

Protective and Pathological Immunity during Central Nervous System Infections

The concept of immune privilege of the central nervous system (CNS) has dominated the study of inflammatory processes in the brain. However, clinically relevant models have highlighted that innate pathways limit pathogen invasion of the CNS and adaptive immunity mediates control of many neural infections. As protective responses can result in bystander damage, there are regulatory mechanisms that balance protective and pathological inflammation, but these mechanisms might also allow microbial persistence. The focus of this review is to consider the host-pathogen interactions that influence neurotropic infections and to highlight advances in our understanding of innate and adaptive mechanisms of resistance as key determinants of the outcome of CNS infection. Advances in these areas have broadened our comprehension of how the immune system functions in the brain and can readily overcome immune privilege.

Adjunctive role of MMP-9 inhibition along with conventional anti-tubercular drugs against experimental tuberculous meningitis

Tuberculous meningitis (TBM) is an outcome of neuroinflammatory degeneration caused due to Mycobacterium tuberculosis infection and leads to death or neurological disabilities in the affected individuals. It causes the highest morbidity and mortality amongst all forms of tuberculosis. Matrix metalloproteinase-9 levels increase and cause inflammatory destruction during progression of the disease. Although corticosteroids are usually given as an adjuvant therapy to overcome these complications, treatment outcome is contradictory. This study was designed to evaluate whether specific inhibition of MMP-9 can be beneficial in management of the disease. MMP-9 levels were inhibited using SB-3CT or dexamethasone along with conventional drugs for treatment of tuberculous meningitis. Both SB-3CT and dexamethasone decreased the elevated levels of MMP-9 in sera and tissues of the infected mice. However, dexamethasone administration had an inhibitory effect on bacillary clearance, while SB-3CT potentiated the bacillary clearance, suggesting that MMP-9, if specifically inhibited, can be beneficial in the management of TBM.

Role of Mycobacterium tuberculosis pknD in the pathogenesis of central nervous system tuberculosis

BACKGROUND

Central nervous system disease is the most serious form of tuberculosis, and is associated with high mortality and severe neurological sequelae. Though recent clinical reports suggest an association of distinct Mycobacterium tuberculosis strains with central nervous system disease, the microbial virulence factors required have not been described previously.

RESULTS

We screened 398 unique M. tuberculosis mutants in guinea pigs to identify genes required for central nervous system tuberculosis. We found M. tuberculosis pknD (Rv0931c) to be required for central nervous system disease. These findings were central nervous system tissue-specific and were not observed in lung tissues. We demonstrated that pknD is required for invasion of brain endothelia (primary components of the blood-brain barrier protecting the central nervous system), but not macrophages, lung epithelia, or other endothelia. M. tuberculosis pknD encodes a "eukaryotic-like" serine-threonine protein kinase, with a predicted intracellular kinase and an extracellular (sensor) domain. Using confocal microscopy and flow cytometry we demonstrated that the M. tuberculosis PknD sensor is sufficient to trigger invasion of brain endothelia, a process which was neutralized by specific antiserum.

CONCLUSIONS

Our findings demonstrate a novel in vivo role for M. tuberculosis pknD and represent an important mechanism for bacterial invasion and virulence in central nervous system tuberculosis, a devastating and understudied disease primarily affecting young children.

Modelling of Cerebral Tuberculosis: Hope for Continuous Research in Solving the Enigma of the Bottom Billion's Disease

Cerebral tuberculosis is a severe type of extrapulmonary disease that is highly predominant in children. It is thought that meningeal tuberculosis, the most common form of cerebral tuberculosis, begins with respiratory infection followed by early haematogenous dissemination to extrapulmonary sites involving the brain. Host genetic susceptibility factors and specific mycobacteria substrains could be involved in the development of this serious form of tuberculosis. In this editorial the different animal models of cerebral tuberculosis are commented, highlighting a recently described murine model in which BALB/c mice were infected by the intratracheal route with clinical isolates, which exhibited rapid dissemination and brain infection. These strains were isolated from the cerebrospinal fluid of patients with meningeal tuberculosis; they showed specific genotype and induced a peculiar immune response in the infected brain. This model could be a useful tool to study host and bacilli factors involved in the pathogenesis of the most severe form of tuberculosis.

Specific bacterial genotypes of Mycobacterium tuberculosis cause extensive dissemination and brain infection in an experimental model

Meningeal tuberculosis is a severe type of extrapulmonary disease, which is thought to begin with respiratory infection, followed by hematogenous dissemination and brain infection. Host genetic susceptibility factors and specific mycobacterial substrains could be involved in its development. From an epidemiological study in Colombia, we selected three Mycobacterium tuberculosis clinical strains isolated from the cerebrospinal fluid (CSF) of patients with meningeal tuberculosis, and used them to infect BALB/c mice through the intratracheal route. These strains showed a distinctive spoligotype pattern. The course of infection in terms of strain virulence (mice survival, bacillary loads in lungs), bacilli dissemination and extrapulmonary infection (bacilli loads in blood, brain, liver, kidney and spleen), and immune responses (cytokine expression determined by real time PCR in brain and lung) was studied and compared with that induced by the laboratory strain H37Rv and other five clinical strains isolated from patients with pulmonary TB. All the clinical isolates from meningeal TB patients disseminated extensively through the hematogenous route infecting the brain, producing inflammation in the cerebral parenchyma and meninges, whereas H37Rv and clinical isolates from pulmonary TB patients showed very limited efficiency to infect the brain. Thus, it seems that mycobacterial strains with a distinctive genotype are able to disseminate extensively after the respiratory infection and infect the brain.

Murine model to study the invasion and survival of Mycobacterium tuberculosis in the central nervous system

BACKGROUND

Tuberculosis of the central nervous system (CNS) is a serious, often fatal disease primarily affecting young children. It develops after hematogenous dissemination and subsequent invasion of the CNS by Mycobacterium tuberculosis. The microbial determinants involved in CNS disease are poorly characterized.

METHODS

Hematogenously disseminated M. tuberculosis infection was simulated in BALB/c mice by intravenous challenge. Bacteria were recovered using standard culture techniques. Host immune response to M. tuberculosis infection was assessed by histopathological and cytokine profile analysis. By means of a pooled infection with genotypically defined M. tuberculosis mutants, bacterial genes required for invasion or survival were determined in the CNS and lung tissue.

RESULTS

M. tuberculosis were detected in whole mouse brains as early as 1 day after intravenous infection and at all time points assessed thereafter. No significant immune response was elicited in the infected brain tissue, compared with extensive inflammation in the infected lung tissue at the same time point. We identified mutants for 5 M. tuberculosis genes (Rv0311, Rv0805, Rv0931c, Rv0986, and MT3280) with CNS-specific phenotypes, absent in lung tissue.

CONCLUSIONS

We have identified CNS-specific M. tuberculosis genes involved in the pathogenesis of tuberculosis. Further characterization of these genes will help in understanding the microbial pathogenesis of CNS tuberculosis.

Identification of Mycobacterium avium pathogenicity island important for macrophage and amoeba infection

The ability to infect macrophages is a common characteristic shared among many mycobacterial species. Mycobacterium avium, Mycobacterium tuberculosis, and Mycobacterium kansasii enter macrophages, using the complement receptors CR1, CR3, CR4, and the mannose receptor. To identify M. avium genes and host cell pathways involved in the bacterial uptake by macrophages, we screened a M. avium transposon mutant library for the inability to enter macrophages. Uptake-impaired clones were selected. Sequence of six M. avium clones identified one gene involved in glycopeptidolipid biosynthesis, one gene encoding the conserved membrane protein homologue to the M. avium subsp. paratuberculosis MAP2446c gene and four others belonging to the same region of the chromosome. Analysis of the chromosome region revealed a pathogenicity island inserted between two tRNA sequences with 58% of G+C content versus 69% in the M. avium genome. The region is unique for M. avium and is not present in M. tuberculosis or M. paratuberculosis. Although the mutants did not differ from the WT bacterium regarding the binding to macrophage cell membrane, analysis of macrophage proteins after 1 h infection revealed a deficiency in the mutant to phosphorylate certain proteins on uptake. To understand M. avium interaction with two evolutionarily distinct hosts, the mutants were evaluated for Acanthamoeba castellanii invasion. The defect in the ability of the mutants to invade both cells was highly similar, suggesting that M. avium might have evolved mechanisms that are used to enter amoebas and human macrophages.

Microbial translocation of the blood–brain barrier

A major contributing factor to high mortality and morbidity associated with CNS infection is the incomplete understanding of the pathogenesis of this disease. Relatively small numbers of pathogens account for most cases of CNS infections in humans, but it is unclear how such pathogens cross the blood-brain barrier (BBB) and cause infections. The development of the in vitro BBB model using human brain microvascular endothelial cells has facilitated our understanding of the microbial translocation of the BBB, a key step for the acquisition of CNS infections. Recent studies have revealed that microbial translocation of the BBB involves host cell actin cytoskeletal rearrangements, most likely as the result of specific microbial-host interactions. A better understanding of microbial-host interactions that are involved in microbial translocation of the BBB should help in developing new strategies to prevent CNS infections. This review summarises our current understanding of the pathogenic mechanisms involved in translocation of the BBB by meningitis-causing bacteria, fungi and parasites.

Inhibition of cytokines expression in human microglia infected by virulent and non-virulent mycobacteria

The pathogenesis of tuberculosis (TBC) meningitis is still unknown. As shown by previous studies, human microglia can be the target of mycobacteria, but no data are available about their cellular response to infection. Consequently, we studied the expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and IL-10 in human microglia pure cultures infected with the two variants of Mycobacterium avium (domed-opaque (SmD) and transparent (SmT)) and with Mycobacterium tuberculosis. Results showed that microglia was productively infected by mycobacteria which could grow inside the cells. Mycobacteria internalization was more rapid for M. avium, but M. tuberculosis infection turned out to be more efficient due to the incorporation of densely packed bacteria. TNF-alpha expression was not affected by M. avium, whereas an increase followed by a decrease was observed in M. tuberculosis. Both IL-1 and IL-10 cytokine expression was rapidly inhibited by infection with the more virulent bacteria, whereas the non-pathogenic one had almost no effect. Also, the expression of the co-stimulatory molecule CD137, a member of tumor necrosis factor receptor family, was affected by infection with virulent mycobacteria. Our results show that microglia response to mycobacterial infection is modulated in correlation with virulence, mainly toward inhibition of inflammatory response. This observation might be one of the mechanisms by which non-pathogenic mycobacteria are quickly eliminated, explaining one of the bases of virulence.

Perspective on animal models: chronic intracellular infections

Systemic human disease caused by organisms of the Mycobacterium avium-Mycobacterium intracellulare complex (MAC) represent a chronic intracellular infection in human hosts who are usually immunocompromised. To develop improved treatment and prophylaxis, and to obtain a better understanding of pathogenesis, we studied the beige mouse (C57 beige(+)/beige(+)) challenged orally or intravenously with a human isolate that causes lethal disease in patients with AIDS (MAC 101, serovar 1). Encouraging anti-MAC studies in animals, as reviewed here, should provide the basis for considering human trials with a promising agent. The ability of an antimicrobial agent to achieve high intracellular concentrations has correlated with the in vivo activity of several specific compounds.

Mycobacterium avium invades the intestinal mucosa primarily by interacting with enterocytes

Previous studies have demonstrated that Mycobacterium avium can invade intestinal epithelial cells both in vitro and in vivo. When given to mice orally, M. avium preferentially interacts with the intestinal mucosa at the terminal ileum. We evaluated the mechanism(s) of M. avium binding and invasion of the intestinal mucosa using three different systems: (i) electron microscopy following administration of M. avium into an intestinal loop in mice, (ii) quantitative comparison of the bacterial load in Peyer's patch areas of the terminal ileum versus areas that do not contain Peyer's patches, and (iii) investigation of the ability of M. avium to cause disseminated infection following oral administration using B-cell-deficient mice, lacking Peyer's patches, in comparison with C57BL/6 black mice. By all approaches, M. avium was found to invade the intestinal mucosa by interacting primarily with enterocytes and not with M cells.