A dynamic reinfection hypothesis of latent tuberculosis infection

Community-Wide Active Case Finding for Tuberculosis: Time to Use the Evidence We Have

Tuberculosis, caused by the Mycobacterium tuberculosis (Mtb) bacteria, is one of the world's deadliest infectious diseases. Despite being the world's oldest pandemic, tuberculosis is very much a challenge of the modern era. In high-incidence settings, all people are at risk, irrespective of whether they have common vulnerabilities to the disease warranting the current WHO recommendations for community-wide tuberculosis active case finding in these settings. Despite good evidence of effectiveness in reducing tuberculosis transmission, uptake of this strategy has been lacking in the communities that would derive greatest benefit. We consider the various complexities in eliminating tuberculosis from the first principles of the disease, including diagnostic and other challenges that must be navigated under an elimination agenda. We make the case that community-wide tuberculosis active case finding is the best strategy currently available to drive elimination forward in high-incidence settings and that no time should be lost in its implementation. Recognizing that high-incidence communities vary in their epidemiology and spatiosocial characteristics, tuberculosis research and funding must now shift towards radically supporting local implementation and operational research in communities. This "preparing of the ground" for scaling up to community-wide intervention centers the local knowledge and local experience of community epidemiology to optimize implementation practices and accelerate reductions in community-level tuberculosis transmission.

Population-wide active case finding as a strategy to end TB

Tuberculosis (TB) is the leading infectious cause of morbidity and mortality globally. Despite available tools for preventing, finding, and treating TB, many people with TB remain undiagnosed. In high-incidence settings, TB transmission is ubiquitous within the community, affecting both high-risk groups and the general population. In fact, most people who develop TB come from the general population. To disrupt the chain of transmission that sustains the TB epidemic, we need to find and treat everyone with infectious TB as early as possible, including those with minimal symptoms or subclinical TB who are unlikely to present for care. Important elements of an effective active case-finding strategy include effective social mobilisation and community engagement, using sensitive screening tools that can be used at scale, and embracing population-wide screening in high-incidence ('hot spot') areas. We require a better description of feasible delivery models, 'real-life' impact and cost effectiveness to enable wider implementation.

Finding and treating both tuberculosis disease and latent infection during population-wide active case finding for tuberculosis elimination

In recognition of the high rates of undetected tuberculosis in the community, the World Health Organization (WHO) encourages targeted active case finding (ACF) among "high-risk" populations. While this strategy has led to increased case detection in these populations, the epidemic impact of these interventions has not been demonstrated. Historical data suggest that population-wide (untargeted) ACF can interrupt transmission in high-incidence settings, but implementation remains lacking, despite recent advances in screening tools. The reservoir of latent infection-affecting up to a quarter of the global population -complicates elimination efforts by acting as a pool from which future tuberculosis cases may emerge, even after all active cases have been treated. A holistic case finding strategy that addresses both active disease and latent infection is likely to be the optimal approach for rapidly achieving sustainable progress toward TB elimination in a durable way, but safety and cost effectiveness have not been demonstrated. Sensitive, symptom-agnostic community screening, combined with effective tuberculosis treatment and prevention, should eliminate all infectious cases in the community, whilst identifying and treating people with latent infection will also eliminate tomorrow's tuberculosis cases. If real strides toward global tuberculosis elimination are to be made, bold strategies are required using the best available tools and a long horizon for cost-benefit assessment.

Latent Tuberculosis in India: An Overview

Treatment of latent tuberculosis infection (LTBI) is essential for tuberculosis (TB) eradication. LTBI patients serve as a reservoir for active TB cases. The WHO's End TB Strategy now prioritises the detection and treatment of LTBI. A comprehensive approach focused on integrated LTBI control is required to accomplish this goal. This review aims to summarise what we know about LTBI in the existing literature, its prominence, diagnostic strategies, and new interventions to alert people of its occurrence and symptoms. We used Medical Subject Heading (MeSH) phrases to search for published publications on the English language in PubMed, Scopus, and Google Scholar. To provide clarity and impact, we examined several government websites to identify the most effective and current treatment regimens. LTBI is a spectrum of infections, such as intermittent, transitory, or progressive, with early, subclinical, and ultimately active TB cases. The global burden of LTBI cannot be firmly established because no "gold-standard" test exists. Screening is advised for high-risk individuals, such as immigrants, occupants and staff members of congregate living facilities, and those who are HIV-positive. The most reliable form of LTBI screening is still the targeted tuberculin skin test (TST). Although LTBI therapy is challenging, for India to become TB-free, it must first focus on testing and treating LTBI. The government should focus on generalising the new diagnostic criteria and adopting a more specific treatment known to all to eliminate TB once and for all.

Surveillance of Daughter Micronodule Formation Is a Key Factor for Vaccine Evaluation Using Experimental Infection Models of Tuberculosis in Macaques

Tuberculosis (TB) is still a major worldwide health problem and models using non-human primates (NHP) provide the most relevant approach for vaccine testing. In this study, we analysed CT images collected from cynomolgus and rhesus macaques following exposure to ultra-low dose Mycobacterium tuberculosis (Mtb) aerosols, and monitored them for 16 weeks to evaluate the impact of prior intradermal or inhaled BCG vaccination on the progression of lung disease. All lesions found (2553) were classified according to their size and we subclassified small micronodules (<4.4 mm) as 'isolated', or as 'daughter', when they were in contact with consolidation (described as lesions ≥ 4.5 mm). Our data link the higher capacity to contain Mtb infection in cynomolgus with the reduced incidence of daughter micronodules, thus avoiding the development of consolidated lesions and their consequent enlargement and evolution to cavitation. In the case of rhesus, intradermal vaccination has a higher capacity to reduce the formation of daughter micronodules. This study supports the 'Bubble Model' defined with the C3HBe/FeJ mice and proposes a new method to evaluate outcomes in experimental models of TB in NHP based on CT images, which would fit a future machine learning approach to evaluate new vaccines.

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

The Origin and Maintenance of Tuberculosis Is Explained by the Induction of Smear-Negative Disease in the Paleolithic

Is it possible that the origin of Mycobacterium tuberculosis (Mtb) infection was around 70,000 years before the common era? At that time Homo sapiens was just another primate species with discrete growth and a very low-density geographic occupation. Therefore, it is difficult to understand the origin of a highly virulent obligate human pathogen. We have designed a new SEIR model (TBSpectr) that allows the differentiation of smear-positive and -negative tuberculosis. The model reconciles currently accepted growth rates for the Middle Paleolithic (0.003%/year) and Neolithic (0.1%/year). The obtained data link the origin of Mtb infection in the Middle Paleolithic to the induction of smear-negative TB, and reveal that its persistence required interrelations among hunter–gatherer groups, while the risk of human extinction was negligible. It also highlights the number of people infected per case and the fast progression to disease for Mtb infection maintenance, as well as the link between poor health in the Neolithic with the increased incidence of more severe forms of TB (smear-positive). In conclusion, our data support the origin of TB as a well-tolerated, highly persistent disease, even in low-density populations, showing the difficulty of its eradication and highlighting the necessity for providing better health conditions to humans to reduce its severity.

How mycobacterium tuberculosis infection could lead to the increasing risks of chronic fatigue syndrome and the potential immunological effects: a population-based retrospective cohort study

Background

Chronic fatigue syndrome (CFS) has been shown to be associated with infections. Tuberculosis (TB) is a highly prevalent infectious disease. Patients with chronic fatigue syndrome and post-tuberculosis experience similar symptoms. Furthermore, chronic fatigue syndrome and tuberculosis share similar plasma immunosignatures. This study aimed to clarify the risk of chronic fatigue syndrome following the diagnosis of Mycobacterium tuberculosis infection (MTI), by analyzing the National Health Insurance Research Database of Taiwan.

Methods

7666 patients aged 20 years or older with newly diagnosed Mycobacterium tuberculosis infection during 2000–2011 and 30,663 participants without Mycobacterium tuberculosis infection were identified. Both groups were followed up until the diagnoses of chronic fatigue syndrome were made at the end of 2011.

Results

The relationship between Mycobacterium tuberculosis infection and the subsequent risk of chronic fatigue syndrome was estimated through Cox proportional hazards regression analysis, with the incidence density rates being 3.04 and 3.69 per 1000 person‐years among the non‐Mycobacterium tuberculosis infection and Mycobacterium tuberculosis infection populations, respectively (adjusted hazard ratio [HR] = 1.23, with 95% confidence interval [CI] 1.03–1.47). In the stratified analysis, the Mycobacterium tuberculosis infection group were consistently associated with a higher risk of chronic fatigue syndrome in the male sex (HR = 1.27, 95% CI 1.02–1.58) and age group of ≥ 65 years old (HR = 2.50, 95% CI 1.86–3.38).

Conclusions

The data from this population‐based retrospective cohort study revealed that Mycobacterium tuberculosis infection is associated with an elevated risk of subsequent chronic fatigue syndrome.

Representing Tuberculosis Transmission with Complex Contagion: An Agent-Based Simulation Modeling Approach

OBJECTIVE

A recent study reported a tuberculosis (TB) outbreak in which, among newly infected individuals, exposure to additional active infections was associated with a higher probability of developing active disease. Referred to as complex contagion, multiple reexposures to TB within a short period after initial infection is hypothesized to confer a greater likelihood of developing active infection in 1 y. The purpose of this article is to develop and validate an agent-based simulation model (ABM) to study the effect of complex contagion on population-level TB transmission dynamics.

METHODS

We built an ABM of a TB epidemic using data from a series of outbreaks recorded in the 20th century in Saskatchewan, Canada. We fit 3 dynamical schemes: base, with no complex contagion; additive, in which each reexposure confers an independent risk of activated infection; and threshold, in which a small number of reexposures confers a low risk and a high number of reexposures confers a high risk of activation.

RESULTS

We find that the base model fits the mortality and incidence output targets best, followed by the threshold and then the additive models. The threshold model fits the incidence better than the base model does but overestimates mortality. All 3 models produce qualitatively realistic epidemic curves.

CONCLUSION

We find that complex contagion qualitatively changes the trajectory of a TB epidemic, although data from a high-incidence setting are reproduced better with the base model. Results from this model demonstrate the feasibility of using ABM to capture nuances in TB transmission.

Heterogeneous Host-Pathogen Encounters Coordinate Antibiotic Resilience in Mycobacterium tuberculosis

Successful treatment of tuberculosis (TB) depends on the eradication of its causative agent Mycobacterium tuberculosis (Mtb) in the host. However, the emergence of phenotypically drug-resistant Mtb in the host environment tempers the ability of antibiotics to cure disease. Host immunity produces diverse microenvironmental niches that are exploited by Mtb to mobilize adaptation programs. Such differential interactions amplify pre-existing heterogeneity in the host-pathogen milieu to influence disease pathology and therapy outcome. Therefore, comprehending the intricacies of phenotypic heterogeneity can be an empirical step forward in potentiating drug action. With this goal, we review the interconnectedness of the lesional, cellular, and bacterial heterogeneity underlying phenotypic drug resistance. Based on this information, we anticipate the development of new therapeutic strategies targeting host-pathogen heterogeneity to cure TB.

A reaction-diffusion model to understand granulomas formation inside secondary lobule during tuberculosis infection

Mycobacterium tuberculosis (Mtb) is the causative agent for tuberculosis, the most extended infectious disease around the world. When Mtb enters inside the pulmonary alveolus it is rapidly phagocytosed by the alveolar macrophage. Although this controls the majority of inhaled microorganisms, in this case, Mtb survives inside the macrophage and multiplies. A posterior chemokine and cytokine cascade generated by the irruption of monocytes, neutrophils and posteriorly, by T-cells, does not necessarily stop the growth of the granuloma. Interestingly, the encapsulation process built by fibroblasts is able to surround the lesion and stop its growing. The success of this last process determines if the host enters in an asymptomatic latent state or continues into a life-threatening and infective active tuberculosis disease (TB). Understanding such dichotomic process is challenging, and computational modeling can bring new ideas. Thus, we have modeled the different stages of the infection, first in a single alveolus (a sac with a radius of 0.15 millimeters) and, second, inside a secondary lobule (a compartment of the lungs of around 3 cm³). We have employed stochastic reaction-diffusion equations to model the interactions among the cells and the diffusive transport to neighboring alveolus. The whole set of equations have successfully described the encapsulation process and determine that the size of the lesions depends on its position on the secondary lobule. We conclude that size and shape of the secondary lobule are the relevant variables to control the lesions, and, therefore, to avoid the evolution towards TB development. As lesions appear near to interlobular connective tissue they are easily controlled and their growth is drastically stopped, in this sense secondary lobules with a more flattened shape could control better the lesion.

Modelling the dynamics of tuberculosis lesions in a virtual lung: Role of the bronchial tree in endogenous reinfection

Tuberculosis (TB) is an infectious disease that still causes more than 1.5 million deaths annually. The World Health Organization estimates that around 30% of the world's population is latently infected. However, the mechanisms responsible for 10% of this reserve (i.e., of the latently infected population) developing an active disease are not fully understood, yet. The dynamic hypothesis suggests that endogenous reinfection has an important role in maintaining latent infection. In order to examine this hypothesis for falsifiability, an agent-based model of growth, merging, and proliferation of TB lesions was implemented in a computational bronchial tree, built with an iterative algorithm for the generation of bronchial bifurcations and tubes applied inside a virtual 3D pulmonary surface. The computational model was fed and parameterized with computed tomography (CT) experimental data from 5 latently infected minipigs. First, we used CT images to reconstruct the virtual pulmonary surfaces where bronchial trees are built. Then, CT data about TB lesion' size and location to each minipig were used in the parameterization process. The model's outcome provides spatial and size distributions of TB lesions that successfully reproduced experimental data, thus reinforcing the role of the bronchial tree as the spatial structure triggering endogenous reinfection. A sensitivity analysis of the model shows that the final number of lesions is strongly related with the endogenous reinfection frequency and maximum growth rate of the lesions, while their mean diameter mainly depends on the spatial spreading of new lesions and the maximum radius. Finally, the model was used as an in silico experimental platform to explore the transition from latent infection to active disease, identifying two main triggering factors: a high inflammatory response and the combination of a moderate inflammatory response with a small breathing amplitude.

Origin of tuberculosis in the Paleolithic predicts unprecedented population growth and female resistance

Current data estimate the origin of Mycobacterium tuberculosis complex (MtbC) infection around 73,000 years before the common era (BCE), and its evolution to “modern” lineages around 46,000 BCE. Being MtbC a major killer of humanity, the question is how both species could persist. To answer this question, we have developed two new epidemiological models (SEIR type), adapted to sex dimorphism and comparing coinfection and superinfection for different MtbC lineages. We have attributed a higher resistance/tolerance to females to explain the lower incidence noted in this sex, a better health status in the Paleolithic compared to the Neolithic, and a higher dissemination of “modern” lineages compared to “ancient” ones. Our findings show the extraordinary impact caused by “modern” lineages, provoking the extinction of the groups infected. This could only be overcomed by an unprecedented population increase (x20 times in 100 years) and helped with the protection generated by previous infection with “ancient” lineages. Our findings also suggest a key role of female resistance against MtbC. This data obliges us to rethink the growth population parameters in the Paleolithic, which is crucial to understanding the survival of both MtbC and humans, and to decipher the nature of human female resistance against TB.

Synergy between Th1 and Th2 responses during Mycobacterium tuberculosis infection: A review of current understanding

Induction of Th1 (cell-mediated) immunity and associated production of IFN-γ by CD4+ T cells has been widely used as a marker of protective immunity against tuberculosis (TB). This is based on two assumptions. The first is the widely accepted view that Mycobacterium tuberculosis (Mtb), the causative agent of TB is an obligate intracellular pathogen, and the second is based on the Th1/Th2 paradigm, which posits that polarization of CD4+ T cells into type1 (cell-mediated) and type 2 (humoral) is central for proper induction of protective immunity against pathogens. However, almost all licensed vaccines currently in use are primarily anti-body based whether intracellular or extra-cellular. In addition, converging data from both animal models and humans indicate that the production of IFN-γ alone is not sufficient to confer protection against TB. In addition, a substantial body of the literature suggests that, in addition to Th1 cells, antibody classes and sub-classes are protective against TB. In a recent study, we have shown that there is a synergy between IFN-γ (cell-mediated) and IgA (humoral) in human population in an endemic setting. In this review, current data from both animal and human studies that support mixed Th1 and Th2 responses that are protective against Mtb and other pathogens are presented.

[The informative value of various methods for identifying acid-fast bacilli in relation to the degree of tuberculosis process activity]

Carbol fuchsin (Ziehl-Neelsen) staining is a major method used since the late nineteenth century to detect Mycobacterium tuberculosis in the tissues. At the same time, the number of mycobacteria does not frequently show a clinical and morphological correspondence to the activity of the infectious process.

OBJECTIVE

To reveal the morphological characteristics of Mycobacterium tuberculosis in patients with long-lasting tuberculosis.

MATERIAL AND METHODS

Twenty-four autopsies of verified fibrous-cavernous tuberculosis were examined. Paraffin sections were stained with hematoxylin and eosin, carbol fuchsin (Ziehl-Neelsen), or auramine-rhodamine (followed by luminescence microscopic examination); an immunohistochemical (IHC) study with serum to PAV (Protein antigen B) was conducted.

RESULTS AND DISCUSSION

The changes characteristic of progressive tuberculosis were revealed in all the cases. The Ziehl-Neelsen staining revealed isolated clusters of acid-fast bacilli (a total of 1,000 in less than 10 fields of view). When stained with auramine-rhodamine, the number of found mycobacteria proved to be significantly larger (a total of 1,000 to 10,000 in 10-50 fields of view) and that was greatest in the IHC study (a total of over 10,000 in more than 50 fields of view). At the same type, all types of studies revealed that the localization of mycobacteria was exclusively extracellular. The Ziehl-Neelsen staining indicated that the proportion of typical bacilli was much higher (85-95%; mean 88.13±2.14) than that (50-85%; mean 64.38±4.24%) identified when stained with auramine-rhodamine and even more significantly more than that (50-70%; mean 57.29±2.78%) detected during the IHC study. The indicators were equally different for the atypical morphological forms of mycobacteria identified in minimal quantities by the Ziehl-Nielsen staining and in large quantities by fluorescence and IHC studies.

CONCLUSION

There is evidence for the ability of mycobacteria to have morphological polymorphism and for the need to clarify the pathogenesis of tuberculosis.

Transcription factors Rv0081 and Rv3334 connect the early and the enduring hypoxic response of Mycobacterium tuberculosis

The ability of Mycobacterium tuberculosis (M. tb) to survive and persist in the host for decades in an asymptomatic state is an important aspect of tuberculosis pathogenesis. Although adaptation to hypoxia is thought to play a prominent role underlying M. tb persistence, how the bacteria achieve this goal is largely unknown. Rv0081, a member of the DosR regulon, is induced at the early stage of hypoxia while Rv3334 is one of the enduring hypoxic response genes. In this study, we uncovered genetic interactions between these two transcription factors. RNA-seq analysis of ΔRv0081 and ΔRv3334 revealed that the gene expression profiles of these two mutants were highly similar. We also found that under hypoxia, Rv0081 positively regulated the expression of Rv3334 while Rv3334 repressed transcription of Rv0081. In addition, we demonstrated that Rv0081 formed dimer and bound to the promoter region of Rv3334. Taken together, these data suggest that Rv0081 and Rv3334 work in the same regulatory pathway and that Rv3334 functions immediately downstream of Rv0081. We also found that Rv3334 is a bona fide regulator of the enduring hypoxic response genes. Our study has uncovered a regulatory pathway that connects the early and the enduring hypoxic response, revealing a transcriptional cascade that coordinates the temporal response of M. tb to hypoxia.

Multiple exposures, reinfection and risk of progression to active tuberculosis

A recent study reported on a tuberculosis (TB) outbreak in a largely Inuit village. Among newly infected individuals, exposure to additional active cases was associated with an increasing probability of developing active disease within a year. Using binomial risk models, we evaluated two potential mechanisms by which multiple infections during the first year following initial infection could account for increasing disease risk with increasing exposures. In the reinfection model, each infectious contact confers an independent risk of an infection, and infections contribute independently to active disease. In the threshold model, disease risk follows a sigmoidal function with small numbers of infectious contacts conferring a low risk of active disease and large numbers of contacts conferring a high risk. To determine the dynamic impact of reinfection during the early phase of infection, we performed simulations from a modified Reed-Frost model of TB dynamics following spread from an initial number of cases. We parametrized this model with the maximum-likelihood estimates from the reinfection and threshold models in addition to the observed distribution of exposures among new infections. We find that both models can plausibly account for the observed increase in disease risk with increasing infectious contacts, but the threshold model confers a better fit than a nested model without a threshold (p = 0.04). Our simulations indicate that multiple exposures to infectious individuals during this critical time period can lead to dramatic increases in outbreak size. In order to decrease TB burden in high-prevalence settings, it may be necessary to implement measures aimed at preventing repeated exposures, in addition to preventing primary infection.

Factors Predicting the Need for Prolonged (>24 Months) Antituberculous Treatment in Patients with Brain Tuberculomas

BACKGROUND

Patients with brain tuberculomas are generally managed with 12-18 months of antituberculous treatment (ATT) with or without surgery. However, a subset of these patients may require ATT for longer periods. We studied the factors that were associated with the need for prolonged ATT (>24 months) in patients with brain tuberculomas.

METHODS

This retrospective study included patients with intracranial tuberculomas managed from January 2000 to December 2015 if they were followed up until completion of therapy and resolution of the tuberculoma/s. The predictive factors analyzed were the number of lesions (solitary vs. multiple), location (infratentorial vs. supratentorial and infratentorial), previous ATT treatment (yes vs. no), surgery (yes vs. no), and size of the lesion (≤2.5 cm vs. >2.5 cm).

RESULTS

Of the 86 patients, 19 (22%) received ATT for >2 years. On multivariate analysis, multiple lesions were significantly associated with the need for prolonged ATT (P = 0.02). Size of the tuberculoma showed a trend toward significance (P = 0.06), with tuberculomas >2.5cm having a 3.68 times increased risk of requiring prolonged ATT.

CONCLUSIONS

Although 78% of brain tuberculomas resolve with 12-24 months of ATT, 22% required >24 months of ATT. Multiple tuberculomas had significant association with prolonged ATT, with a median duration of resolution of 36 months. Because tuberculomas >2.5 cm were likely to need longer duration of ATT, brain tuberculomas that require surgery should be excised totally or reduced in size to <2.5 cm to enable early resolution.

Comparison of IFN-γ Levels in Children with Tuberculosis Disease (TB) and Latent Tuberculosis Infection (LTBI)

AIM:

This study aimed to evaluate the importance of IFN-γ in the diagnosis of pediatric TB and LTBI and to compare the IFN-γ levels.

METHODS:

We analysed 100 patients examined for possible M. tuberculosis infection or disease at the Institute of Respiratory Diseases in Children, Kozle, Skopje. Patients were divided into 2 groups: TB disease and LTBI. The following parameters were analyzed: demographic characteristics, history of previous exposure to active TB, BCG vaccination and presence of BCG scar, lung X-ray findings, tuberculin skin test by the Monteux method and the value of INF-γ according to the Quantiferon TB gold test, direct samples of acid-alcohol-resistant bacilli of sputum and Löwenstein Jensen cultures. Informed parental consent was obtained for each child included in the study.

RESULTS:

In the LTBI group 60.9% had a scar from the vaccination while in the TB group 50% had BCG scar. TST induration diameters in children with or without BCG scar were significantly larger in patients with active TB. Children with active TB had significantly higher IFN-γ levels than children with LTBI. The IFN-γ for the cut-off of 0.35 IU/ml, has 64% sensitivity for detection of LTBI, versus 80.6% sensitivity for active disease. Children with close TB contact had significantly higher IFN-γ levels. Correlation between TST induration diameter and IFN-γ levels was stronger in the TB group.

CONCLUSION:

IFN-γ levels are significantly higher in children with active TB, and children with close contact with TB patient. It has better sensitivity in active TB. Using both tests (IFN-γ and TST) can improve the diagnose of LTBI and TB in countries where vaccination with BCG is widespread.

PE_PGRS3 of Mycobacterium tuberculosis is specifically expressed at low phosphate concentration, and its arginine-rich C-terminal domain mediates adhesion and persistence in host tissues when expressed in Mycobacterium smegmatis

PE_PGRSs of Mycobacterium tuberculosis (Mtb) represent a family of complex and peculiar proteins whose role and function remain elusive. In this study, we investigated PE_PGRS3 and PE_PGRS4, two highly homologous PE_PGRSs encoded by two contiguous genes in the Mtb genome. Using a gene-reporter system in Mycobacterium smegmatis (Ms) and transcriptional analysis in Mtb, we show that PE_PGRS3, but not PE_PGRS4, is specifically expressed under low phosphate concentrations. Interestingly, PE_PGRS3, but not PE_PGRS4, has a unique, arginine-rich C-terminal domain of unknown function. Heterologous expression of PE_PGRS3 in Ms was used to demonstrate cellular localisation of the protein on the mycobacterial surface, where it significantly affects net surface charge. Moreover, expression of full-length PE_PGRS3 enhanced adhesion of Ms to murine macrophages and human epithelial cells and improved bacterial persistence in spleen tissue following infection in mice. Expression of the PE_PGRS3 functional deletion mutant lacking the C-terminal domain in Ms did not enhance adhesion to host cells, showing a phenotype similar to the Ms parental strain. Interestingly, enhanced persistence of Ms expressing PE_PGRS3 did not correlate with increased concentrations of inflammatory cytokines. These results point to a critical role for the ≈ 80 amino acids long, arginine-rich C-terminal domain of PE_PGRS3 in tuberculosis pathogenesis.

Pathogenesis of Mycobacterium bovis Infection: the Badger Model As a Paradigm for Understanding Tuberculosis in Animals

Tuberculosis in animals is caused principally by infection with Mycobacterium bovis and the potential for transmission of infection to humans is often the fundamental driver for surveillance of disease in livestock and wild animals. However, with such a vast array of species susceptible to infection, it is often extremely difficult to gain a detailed understanding of the pathogenesis of infection--a key component of the epidemiology in all affected species. This is important because the development of disease control strategies in animals is determined chiefly by an understanding of the epidemiology of the disease. The most revealing data from which to formulate theories on pathogenesis are that observed in susceptible hosts infected by natural transmission. These data are gathered from detailed studies of the distribution of gross and histological lesions, and the presence and distribution of infection as determined by highly sensitive bacteriology procedures. The information can also be used to establish the baseline for evaluating experimental model systems. The European badger (Meles meles) is one of a very small number of wild animal hosts where detailed knowledge of the pathogenesis of M. bovis infection has been generated from observations in natural-infected animals. By drawing parallels from other animal species, an experimental badger infection model has also been established where infection of the lower respiratory tract mimics infection and the disease observed in natural-infected badgers. This has facilitated the development of diagnostic tests and testing of vaccines that have the potential to control the disease in badgers. In this review, we highlight the fundamental principles of how detailed knowledge of pathogenesis can be used to evaluate specific intervention strategies, and how the badger model may be a paradigm for understanding pathogenesis of tuberculosis in any affected wild animal species.

Pathogenesis of tuberculosis and other mycobacteriosis

The evolution between Mycobacterium tuberculosis infection and active tuberculosis is multifactorial and involves different biological scales. The synthesis of ESAT-6 or the induction of alveolar macrophage necrosis are key, but to understand it, it is necessary to consider the dynamics of endogenous and exogenous reinfection, drainage of lung parenchyma and respiratory mechanics, local fibrosis processes and blood supply. Paradoxically, the immune response generated by the infection is highly protective (90%) against active tuberculosis, although as it is essentially based on the proliferation of Th1 lymphocytes, it cannot prevent reinfection. Severe immunosuppression can only explain 10% of active tuberculosis cases, while the remainder are attributable to comorbidities, a proinflammatory environment and an unknown genetic propensity. The pathogenic capacity of environmental mycobacteria is discrete, linked to deficits in the innate and acquired immune response. The ability to generate biofilms and the ability of M. ulcerans to generate the exotoxin mycolactone is remarkable.

What We Have Learned and What We Have Missed in Tuberculosis Pathophysiology for a New Vaccine Design: Searching for the "Pink Swan"

This is a call to encourage the search for a new vaccine to stop the progression of Mycobacterium tuberculosis infection to tuberculosis (TB) disease. TB is a highly discreet and stigmatized disease, with a massive impact on human health. It has killed 1.2 billion people in the last 200 years and still kills 1.5 million people per year. Over the last 20 years, the TB vaccine field has experienced spectacular developments, and we have learned about (1) the importance of the Th1 response in controlling infection, mainly against RD1 and Ag85 antigens; (2) the stability of the antigenic repertoire; (3) the dynamics of M. tuberculosis granulomas; or (4) the link between typical and atypical pulmonary TB and the immune status of the host. However, we still do not (1) know how to avoid M. tuberculosis infection and reinfection; (2) understand the major role of the increase in lesion size in progression from infection to disease; (3) the role of interlobular septa in encapsulating pulmonary lesions; or (4) the role of neutrophilic infiltration and an exaggerated inflammatory response in the development of TB disease. These are strong reasons to pursue new, imaginative proposals involving both the antibody response and a balanced, tolerant immune response that averts progression toward TB. So far, the scientific mindset has been quite monolithic and has mainly focused on the stimulation of conventional T cells. But this approach has failed. For that reason, we are seeking unconventional perspectives to find a “pink swan,” a more efficacious and safer vaccine candidate.

Sequence analysis of haemagglutinin and neuraminidase of H1N1 strain from a patient coinfected with Mycobacterium tuberculosis

The 2009 H1N1 pandemic (H1N1pdm09) was associated with a considerable influenza-related morbidity and mortality. Among the complications, Mycobacterial tuberculosis was recorded as a coinfection with influenza in rare cases. The full-length sequences of the viral haemagglutinin and neuraminidase of H1N1pdm09 influenza A virus were analyzed from a recently infected patient. The patient was chronically infected with Mycobacterium tuberculosis. Molecular modelling and in-silico docking of the virus, and other selected strains with the drug oseltamivir were conducted and compared. Sequence analysis of the viral haemagglutinin revealed it to be closely related to the 6B.1 clade, with high identity to the circulating H1N1pdm09 strains, and confirmed that the virus still harbouring high affinity to the α-2,6-sialic acid human receptor. The viral neuraminidase showed high identity to the neuraminidase of the recently circulating strains of the virus with no evidence of the development of oseltamivir-resistant mutants. Regular monitoring of the circulating strains is recommended to screen for a possible emergence of drug-resistant strains.

Reactivation or reinfection in adult tuberculosis: Is that the question?

Looking at the chapter on "natural history" in any tuberculosis (TB) reference book, there is a kind of certainty regarding TB in adults. That is the concept of "post-primary" TB described as the reactivation of dormant bacilli hidden in an old lesion developed during infancy due to a type of local immunosuppression. Intriguingly, this concept involves at least two major uncertainties: how can dormant bacilli remain for such a long period, almost a lifetime, in an old lesion, taking into account granuloma dynamism; and what sort of local immunosuppression is the one that facilitates reactivation? The controversy between reactivation and exogenous reinfection as the cause of active TB started very soon in TB research. Interestingly, this "balance" was disturbed in the 1960s when the "Unitary Concept" became very successful in supporting the reactivation dogma. The "Unitary Concept" was mainly based on the data of tuberculin surveillance during the pre-antibiotic era as well as the data obtained from experimental modelling in animals. At the same time, the "Three-risks model" appeared to explain the relationship between the risk of infection and TB incidence, granting reinfection a key role in adult TB together with primary infection. This role was reinforced by the studies of recurrence based on molecular epidemiology, and a better knowledge of the immune response, granuloma dynamics, and lung physiology. Now it is a matter of taking it into account when designing new prophylactic and therapeutic strategies and also reflecting it in text books to better illustrate to our students.

The Progress of Therapeutic Vaccination with Regard to Tuberculosis

A major problem with tuberculosis (TB) control is the long duration of drug therapy-both for latent and for active TB. Therapeutic vaccination has been postulated to improve this situation, and to this end there are several candidates already in clinical phases of development. These candidates follow two main designs, namely bacilli-directed therapy based on inactivated -whole or -fragmented bacillus (Mycobacterium w and RUTI) or fusion proteins that integrate non-replicating bacilli -related antigens (H56 vaccine), and host-directed therapy to reduce the tissue destruction. The administration of inactivated Mycobacterium vaccae prevents the "Koch phenomenon" response, and oral administration of heat-killed Mycobacterium manresensis prevents excessive neutrophilic infiltration of the lesions. This review also tries to explain the success of Mycobacterium tuberculosis by reviewing its evolution from infection to disease, and highlights the lack of a definitive understanding of the natural history of TB pathology and the need to improve our knowledge on TB immunology and pathogenesis.

Local Inflammation, Dissemination and Coalescence of Lesions Are Key for the Progression toward Active Tuberculosis: The Bubble Model

The evolution of a tuberculosis (TB) infection toward active disease is driven by a combination of factors mostly related to the host response. The equilibrium between control of the bacillary load and the pathology generated is crucial as regards preventing the growth and proliferation of TB lesions. In addition, some experimental evidence suggests an important role of both local endogenous reinfection and the coalescence of neighboring lesions. Herein we propose a mathematical model that captures the essence of these factors by defining three hypotheses: (i) lesions grow logistically due to the inflammatory reaction; (ii) new lesions can appear as a result of extracellular bacilli or infected macrophages that escape from older lesions; and (iii) lesions can merge when they are close enough. This model was implemented in Matlab to simulate the dynamics of several lesions in a 3D space. It was also fitted to available microscopy data from infected C3HeB/FeJ mice, an animal model of active TB that reacts against Mycobacterium tuberculosis with an exaggerated inflammatory response. The results of the simulations show the dynamics observed experimentally, namely an initial increase in the number of lesions followed by fluctuations, and an exponential increase in the mean area of the lesions. In addition, further analysis of experimental and simulation results show a strong coincidence of the area distributions of lesions at day 21, thereby highlighting the consistency of the model. Three simulation series removing each one of the hypothesis corroborate their essential role in the dynamics observed. These results demonstrate that three local factors, namely an exaggerated inflammatory response, an endogenous reinfection, and a coalescence of lesions, are needed in order to progress toward active TB. The failure of one of these factors stops induction of the disease. This mathematical model may be used as a basis for developing strategies to stop the progression of infection toward disease in human lungs.

Activity of Medicinal Plant Extracts on Multiplication of Mycobacterium tuberculosis under Reduced Oxygen Conditions Using Intracellular and Axenic Assays

Aim. Test the activity of selected medicinal plant extracts on multiplication of Mycobacterium tuberculosis under reduced oxygen concentration which represents nonreplicating conditions. Material and Methods. Acetone, ethanol and aqueous extracts of the plants Acorus calamus L. (rhizome), Ocimum sanctum L. (leaf), Piper nigrum L. (seed), and Pueraria tuberosa DC. (tuber) were tested on Mycobacterium tuberculosis H37Rv intracellularly using an epithelial cell (A549) infection model. The extracts found to be active intracellularly were further studied axenically under reducing oxygen concentrations. Results and Conclusions. Intracellular multiplication was inhibited ≥60% by five of the twelve extracts. Amongst these 5 extracts, in axenic culture, P. nigrum (acetone) was active under aerobic, microaerophilic, and anaerobic conditions indicating presence of multiple components acting at different levels and P. tuberosa (aqueous) showed bactericidal activity under microaerophilic and anaerobic conditions implying the influence of anaerobiosis on its efficacy. P. nigrum (aqueous) and A. calamus (aqueous and ethanol) extracts were not active under axenic conditions but only inhibited intracellular growth of Mycobacterium tuberculosis, suggesting activation of host defense mechanisms to mediate bacterial killing rather than direct bactericidal activity.

Dynamics of the T cell response to Mycobacterium tuberculosis DosR and Rpf antigens in a Colombian population of household contacts of recently diagnosed pulmonary tuberculosis patients

Immune response to DosR and Rpf antigens from Mycobacterium tuberculosis (Mtb) seems to be important for latency maintenance. Little is known about the dynamics of the immune response to these antigens in an endemic community. Thus, the IFNγ response and cytokine production in response to PPD, Esat6-Cfp10 (E6-C10), DosR and Rpf antigens in healthy HHC of tuberculosis (TB) patients over a 12 (T12) months period (short-term, stLTBI) was investigated. This response was compared with a group of LTBI, who have remained healthy for 5-7 years (long-term, ltLTBI). According to the IFNγ response, two groups of HHCs were identified in stLTBI in response to E6-C10. At T12, E6-C10(+) HHCs displayed a decrease in the IFNγ levels and a generalized decrease in cytokines production. The E6-C10(-) HHC showed an increase in the IFNγ response and cytokine levels. In stLTBI, the responses to E6-C10, DosR, and Rpf may be interpreted as a protective immune response controlling Mtb infection and may be leading to a state of latent infection. Comparing the response of stLTBI and ltLTBI, we observed significant changes in the proportions of CD45RO(+)CD27(+) T cells to specific DosR and Rpf, which may indicate a persistent immune response to Mtb antigens in ltLTBI.

The tuberculosis spectrum: Translating basic research into pediatric clinical practice

Recent studies suggest that the classical dichotomous classification of "active" and "latent" tuberculosis (TB) is no longer acceptable since "TB infection" encompasses a wide spectrum of conditions ranging from asymptomatic to lethal disease. In an attempt to address these issues from a pediatric clinical perspective, we describe two children with microbiologically confirmed TB but lacking any clinical and radiological evidence of disease. These two cases highlight the hypothesis that TB cannot be divided in two simple categories, but it covers a wide spectrum of manifestations ranging from asymptomatic to lethal TB. The implications of these results in the context of the new TB spectrum and the related clinical issues are discussed.

Mycobacterium tuberculosis virulence: insights and impact on vaccine development

The existing TB vaccine, the attenuated Mycobacterium bovis strain BCG, is effective in protecting infants from severe forms of the disease, while its efficacy in protecting adults from pulmonary TB is poor. In the last two decades, a renewed interest in TB resulted in the development of several candidate vaccines that are now entering clinical trials. However, most of these vaccines are based on a common rationale and aim to induce a strong T-cell response against Mycobacterium tuberculosis. Recent advancements in the understanding of M. tuberculosis virulence determinants and associated pathogenic strategies are opening a new and broader view of the complex interaction between this remarkable pathogen and the human host, providing insights at molecular level that could lead to a new rationale for the design of novel antitubercular vaccines. A vaccination strategy that simultaneously targets different steps in TB pathogenesis may result in improved protection and reduced TB transmission.

The key role of exudative lesions and their encapsulation: lessons learned from the pathology of human pulmonary tuberculosis

A review of the pathology of human pulmonary TB cases at different stages of evolution in the pre-antibiotic era suggests that neutrophils play an instrumental role in the progression toward active TB. This progression is determined by the type of lesion generated. Thus, exudative lesions, in which neutrophils are the major cell type, are both triggered by and induce local high bacillary load, and tend to enlarge and progress toward liquefaction and cavitation. In contrast, proliferative lesions are triggered by low bacillary loads, mainly comprise epithelioid cells and fibroblasts and tend to fibrose, encapsulate and calcify, thus controlling the infection. Infection of the upper lobes is key to the progression toward active TB for two main reasons, namely poor breathing amplitude, which allows local bacillary accumulation, and the high mechanical stress to which the interlobular septae (which enclose secondary lobes) are submitted, which hampers their ability to encapsulate lesions. Overall, progressing factors can be defined as internal (exudative lesion, local bronchogenous dissemination, coalescence of lesions), with lympho-hematological dissemination playing a very limited role, or external (exogenous reinfection). Abrogating factors include control of the bacillary load and the local encapsulation process, as directed by interlobular septae. The age and extent of disease depend on the quality and speed with which lesions liquefy and disseminate bronchially, the volume of the slough, and the amount and distribution of the sloughing debris dispersed.

Tuberculosis vaccine types and timings

Traditionally, the design of new vaccines directed against Mycobacterium tuberculosis, the most successful bacterial pathogen on the planet, has focused on prophylactic candidates that would be given to individuals while they are still young. It is becoming more apparent, however, that there are several types of vaccine candidates now under development that could be used under various conditions. Thus, in addition to prophylactic vaccines, such as recombinant Mycobacterium bovis BCG or BCG-boosting vaccines, other applications include vaccines that could prevent infection, vaccines that could be given in emergency situations as postexposure vaccines, vaccines that could be used to facilitate chemotherapy, and vaccines that could be used to reduce or prevent relapse and reactivation disease. These approaches are discussed here, including the type of immunity we are trying to specifically target, as well as the limitations of these approaches.

Vaccines to prevent tuberculosis infection rather than disease: Physiological and immunological aspects

There is increasing enthusiasm and optimism that a vaccine could be developed that prevents infection rather than disease. In this article I discuss the fact that despite this optimism nothing has been produced so far that seems to have this capability, and moreover even the borderline between when infection ends and disease begins has not even been defined. To be effective such a vaccine, or at least the immunity it would generate, would have to work within the confines of the pulmonary physiological systems, which are complex. To date much of the emphasis here has turned away from T cell mediated immunity and towards establishing specific antibodies in the lungs. Here, I argue that with the exception of a possible exclusionary function, most claims of a protective role of antibody are completely over-blown. Finally, even if we had a potential "anti-infection" vaccine, how would we test and validate it?

To achieve an earlier IFN-γ response is not sufficient to control Mycobacterium tuberculosis infection in mice

The temporo-spatial relationship between the three organs (lung, spleen and lymph node) involved during the initial stages of Mycobacterium tuberculosis infection has been poorly studied. As such, we performed an experimental study to evaluate the bacillary load in each organ after aerosol or intravenous infection and developed a mathematical approach using the data obtained in order to extract conclusions. The results showed that higher bacillary doses result in an earlier IFN-γ response, that a certain bacillary load (BL) needs to be reached to trigger the IFN-γ response, and that control of the BL is not immediate after onset of the IFN-γ response, which might be a consequence of the spatial dimension. This study may have an important impact when it comes to designing new vaccine candidates as it suggests that triggering an earlier IFN-γ response might not guarantee good infection control, and therefore that additional properties should be considered for these candidates.

Multiple consecutive infections might explain the lack of protection by BCG

Although contacts between tuberculosis patients may result in multiple consecutive infections (MCI), no experimental animal models consider this fact when used in basic studies. Moreover, the current TB vaccine (BCG) has demonstrated a limited protection in humans. In this study we evaluate the effect of tuberculosis MCI by way of a simple mathematical analysis using data from the low dose aerosol murine experimental model. The results show that a higher number of, or shorter intervals between, multiple consecutive infections reduce the protective effect of BCG. This is due to both the increase in bacillary load at the stationary level of the infection, and the protective immune response induced by the infection itself. This factor must therefore be taken into account when designing new prophylactic strategies as candidate vaccines for the replacement of BCG.

Tuberculosis in patients with haematological malignancies

Tuberculosis (TB) is an infectious disease that causes more than 1 million deaths worldwide every year. In addition, it is estimated that one third of the world population is infected with M. tuberculosis in a latent state, which involves an eventual risk of progressing to active TB disease. Patients with immunodeficiencies, such as those suffering from haematological malignancies, have a greater risk of progressing to TB disease once infected. It is estimated that the Relative Risk of TB disease in patients with hematologic malignancies is 2–40 times that of the general population. The diagnosis of TB in these patients is often challenging as they often present clinical characteristics that are distinct to those of patients without any other underlying disease. Mortality due to TB is higher. Therefore, it is recommended to diagnose latent TB infection and consider preventive therapy that could avoid the progression from a latent state to active TB disease. There are currently two methods for diagnosing latent TB infection: the Tuberculin Skin Test (TST) and the Interferon-Gamma Release Assays (IGRA). Due to the lack of sensitivity in patients with immunodeficient conditions, a combined TST-IGRA testing is probably the best way for latent TB diagnosis in order to gain sensitivity. Treatment of latent TB infection and TB disease should follow the general principles to that in the general population.

Safety, tolerability, and immunogenicity of the novel antituberculous vaccine RUTI: randomized, placebo-controlled phase II clinical trial in patients with latent tuberculosis infection

Objectives

To evaluate the safety, tolerability and immunogenicity of three different doses (5, 25 and 50 µg) of the novel antituberculous vaccine RUTI compared to placebo in subjects with latent tuberculosis infection.

Methods and Findings

Double-blind, randomized, placebo-controlled Phase II Clinical Trial (95 patients randomized). Three different RUTI doses and placebo were tested, randomized both in HIV-positive (n = 47) and HIV-negative subjects (n = 48), after completion of one month isoniazid (INH) pre-vaccination. Each subject received two vaccine administrations, 28 Days apart. Five patients withdrew and 90 patients completed the study. Assessment of safety showed no deaths during study. Two subjects had serious adverse events one had a retinal detachment while taking INH and was not randomized and the other had a severe local injection site abscess on each arm and was hospitalized; causality was assessed as very likely and by the end of the study the outcome had resolved. All the patients except 5 (21%) patients of the placebo group (3 HIV+ and 2 HIV−) reported at least one adverse event (AE) during the study. The most frequently occurring AEs among RUTI recipients were (% in HIV+/−): injection site reactions [erythema (91/92), induration (94/92), local nodules (46/25), local pain (66/75), sterile abscess (6/6), swelling (74/83), ulcer (20/11), headache (17/22) and nasopharyngitis (20/5)]. These events were mostly mild and well tolerated. Overall, a polyantigenic response was observed, which differed by HIV− status. The best polyantigenic response was obtained when administrating 25 µg RUTI, especially in HIV-positive subjects which was not increased after the second inoculation.

Conclusion

This Phase II clinical trial demonstrates reasonable tolerability of RUTI. The immunogenicity profile of RUTI vaccine in LTBI subjects, even being variable among groups, allows us considering one single injection of one of the highest doses in future trials, preceded by an extended safety clinical phase.

Trial Registration

ClinicalTrials.gov NCT01136161

The lack of a big picture in tuberculosis: the clinical point of view, the problems of experimental modeling and immunomodulation. The factors we should consider when designing novel treatment strategies

This short review explores the large gap between clinical issues and basic science, and suggests why tuberculosis research should focus on redirect the immune system and not only on eradicating Mycobacterium tuberculosis bacillus. Along the manuscript, several concepts involved in human tuberculosis are explored in order to understand the big picture, including infection and disease dynamics, animal modeling, liquefaction, inflammation and immunomodulation. Scientists should take into account all these factors in order to answer questions with clinical relevance. Moreover, the inclusion of the concept of a strong inflammatory response being required in order to develop cavitary tuberculosis disease opens a new field for developing new therapeutic and prophylactic tools in which destruction of the bacilli may not necessarily be the final goal.

Identification of latent tuberculosis infection-related microRNAs in human U937 macrophages expressing Mycobacterium tuberculosis Hsp16.3

Background

Latent tuberculosis infection (LTBI) relies on a homeostasis of macrophages and Mycobacterium tuberculosis (Mtb). The small heat shock protein, Mtb Hsp16.3 (also known as latency-associated antigen), plays an important role in Mtb persistence within macrophages. However, the mechanism of LTBI remains elusive. The aim of this study was to delineate LTBI-related miRNA expression in U937 macrophages expressing Mtb Hsp16.3 protein. U937 macrophages were infected with an integrase-deficient Lentivirus vector to transiently express Mtb Hsp16.3, and green fluorescent protein (GFP) as a control. We used a microRNA (miRNA) microarray chip containing more than 1000 probes to identify the significant differentially expressed miRNAs in the infected U937 cells, and employed real-time quantitative polymerase chain reaction (qRT-PCR) for validation. Furthermore, we confirmed these candidate LTBI-related miRNAs in peripheral blood mononuclear cells from subjects with LTBI and in healthy control individuals. Functional annotation prediction of miRNA target genes and pathway enrichment analyses were used to explore the putative links between these miRNAs and LTBI.

Results

Analysis of the miRNA expression profile identified 149 miRNAs that were differentially expressed in U937 macrophages expressing Mtb Hsp16.3 compared with the control expressing GFP. The expression level of seven miRNAs (miR-424-5p, miR-493-5p, miR-296-5p, miR-27b-3p, miR-377-5p, miR-3680-5p, miR-191-5p) were validated by qRT-PCR. The expression level of four miRNAs (miR-424-5p, miR-27b-3p, miR-377-5p, miR-3680-5p) in the peripheral blood mononuclear cells samples from LTBI and healthy participants reflected the altered patterns observed in the microarray profile. The bioinformatic analyses suggest that the miRNAs may regulate Mtb latent infection by affecting the development of macrophage cells.

Conclusions

The results suggest that miRNA expression may play a considerable role in the pathogenesis of LTBI, and this would increase our understanding of the molecular basis of Hsp16.3-facilitated Mtb survival in macrophages.

Damaging role of neutrophilic infiltration in a mouse model of progressive tuberculosis

Tuberculosis was studied using an experimental model based on the C3HeB/FeJ mouse strain, which mimics the liquefaction of caseous necrosis occurring during active disease in immunocompetent adults. Mice were intravenously infected with 2 × 10(4) Colony Forming Units of Mycobacterium tuberculosis and their histopathology, immune response, bacillary load, and survival were evaluated. The effects of the administration of drugs with anti-inflammatory activity were examined, and the C3H/HeN mouse strain was also included for comparative purposes. Massive intra-alveolar neutrophilic infiltration led to rapid granuloma growth and coalescence of lesions into superlesions. A central necrotic area appeared showing progressive cellular destruction, the alveoli cell walls being initially conserved (caseous necrosis) but finally destroyed (liquefactive necrosis). Increasing levels of pro-inflammatory mediators were detected in lungs. C3HeB/FeJ treated with anti-inflammatory drugs and C3H/HeN animals presented lower levels of pro-inflammatory mediators such as TNF-α, IL-17, IL-6 and CXCL5, a lower bacillary load, better histopathology, and increased survival compared with untreated C3HeB/FeJ. The observation of massive neutrophilic infiltration suggests that inflammation may be a key factor in progression towards active tuberculosis. On the basis of our findings, we consider that the C3HeB/FeJ mouse model would be useful for evaluating new therapeutic strategies against human tuberculosis.

Evolution and role of corded cell aggregation in Mycobacterium tuberculosis cultures

The aim of this study was to evaluate the evolution and role of corded cell aggregation in Mycobacterium tuberculosis cultures according to growth time and conditions. Thus, in standard culture using aerated 7H9 Middlebrook broth supplemented with 0.05% Tween 80, a dramatic CFU decrease was observed at the end of the exponential phase. This phase was followed by a stable stationary phase that led to dissociation between the optical density (O.D.) and CFU values, together with the formation of opaque colonies in solid culture. Further analysis revealed that this was due to cording. Scanning electron microscopy showed that cording led to the formation of very stable coiled structures and corded cell aggregations which proved impossible to disrupt by any of the physical means tested. Modulation of cording with a high but non-toxic concentration of Tween 80 led to a slower growth rate, avoidance of a sudden drop-off to the stationary phase, the formation of weaker cording structures and the absence of opaque colonies, together with a lower survival at later time-points. An innovative automated image analysis technique has been devised to characterize the cording process. This analysis has led to important practical consequences for the elaboration of M. tuberculosis inocula and suggests the importance of biofilm formation in survival of the bacilli in the extracellular milieu.