Method for assessing IFN-γ responses in guinea pigs during TB vaccine trials

Aims: We sought to develop a new method that enables the assessment of the immune response of guinea pigs during TB vaccine evaluation studies, without the need to cull or anaesthetize animals. Method and Results: Guinea pigs were vaccinated with five different formulations of oral BCG. One week prior to challenge with Mycobacterium bovis, blood (50–200 μl) was taken from the ears of vaccinated subjects. Host RNA was isolated and amplified following antigenic restimulation of PBMCs for 24 h with 30 μg of bovine PPD. The up‐ or down‐regulation of γ‐interferon (IFN‐γ), a key cytokine involved in protection against tuberculosis, was assessed using real‐time PCR. The relative expression of prechallenge IFN‐γ mRNA in the vaccinated groups (n = 5) correlated (P < 0·001) with protection against M. bovis challenge. Conclusion: We have demonstrated that it is possible to take blood samples and track IFN‐γ responses in guinea pigs that then go on to be exposed to M. bovis, thus providing prechallenge vaccine uptake information. Significance and Impact of the Study: This methodology will also be applicable for tracking the immune responses of vaccinated guinea pigs over time that then go on to be challenged with M. tuberculosis during human TB vaccine evaluation studies.     

Detection of anti-tuberculosis activity in some folklore plants by radiometric BACTEC assay

Aims: The anti‐tubercular drugs are less effective because of the emergence of multi‐drug resistant (MDR) and extensively drug resistant (XDR) strains of M. tuberculosis, so plants being an alternative source of anti‐microbial compounds. The aim of this study was to investigate anti‐tuberculosis potential of the plants using Mycobacterium smegmatis as a rapid screening model for detection of anti‐mycobacterial activity and further to evaluate the active plants for anti‐tuberculosis activity against M. tuberculosis using radiometric BACTEC assay. Methods and Results: The 15 plants were screened for anti‐mycobacterial activity against M. smegmatis by the disk diffusion assay. The ethanolic extracts of Mallotus philippensis, Vitex negundo, Colebrookea oppositifolia, Rumex hastatus, Mimosa pudica, Kalanchoe integra and Flacourtia ramontchii were active against M. smegmatis in primary screening. The anti‐tuberculosis potential was identified in the leaves extracts of Mallotus philippensis by radiometric BACTEC assay. The ethanolic extract of M. philippensis showed anti‐tuberculosis activity against virulent and avirulent strains of M. tuberculosis H₃₇Rv and M. tuberculosis H₃₇Ra with minimum inhibitory concentration 0·25 and 0·125 mg ml^?1, respectively. The inhibition in growth index values of M. tuberculosis was observed in the presence of ethyl acetate fraction at a minimum concentration of 0·05 mg ml^?1. Conclusion: We found that BACTEC radiometric assay is a valuable method for detection of anti‐tuberculosis activity of the plant extracts. The results indicate that ethanolic extract and ethyl acetate fraction of M. philippensis exhibited significant anti‐mycobacterial activity against M. tuberculosis. Significance and Impact of the Study: These findings provide scientific evidence to support the traditional medicinal uses of M. philippensis and indicate a promising potential of this plant for the development of anti‐tuberculosis agent.     

Protective efficacy of different cell-wall fractions ofMycobacterium tuberculosis

Immunization with various cell-wall fractions ofM. tuberculosis H₃₇Ra, progressively depleted of lipids (cell-wall-insoluble fraction; CWIF), soluble proteins (cell-wall core; CWC), mycolic acids and arabinogalactans (cell-wall-protein-peptidoglycan complex; CW-PPC) elicited significant levels of both humoral and cell-mediated immune response. Mice immunized with these fractions, when challenged with an LD₅₀ dose ofM. tuberculosis H₃₇Rv, exhibited significant protection as revealed by high survival rates and decreased bacterial load in lungs, liver and spleen, as compared to nonimmunized animals.     

The Impact of Mouse Passaging of Mycobacterium tuberculosis Strains prior to Virulence Testing in the Mouse and Guinea Pig Aerosol Models

Background

It has been hypothesized that the virulence of lab-passaged Mycobacterium tuberculosis and recombinant M. tuberculosis mutants might be reduced due to multiple in vitro passages, and that virulence might be augmented by passage of these strains through mice before quantitative virulence testing in the mouse or guinea pig aerosol models.

Methodology/Principal Findings

By testing three M. tuberculosis H37Rv samples, one deletion mutant, and one recent clinical isolate for survival by the quantitative organ CFU counting method in mouse or guinea pig aerosol or intravenous infection models, we could discern no increase in bacterial fitness as a result of passaging of M. tuberculosis strains in mice prior to quantitative virulence testing in two animal models. Surface lipid expression as assessed by neutral red staining and thin-layer chromatography for PDIM analysis also failed to identify virulence correlates.

Conclusions/Significance

These results indicate that animal passaging of M. tuberculosis strains prior to quantitative virulence testing in mouse or guinea pig models does not enhance or restore potency to strains that may have lost virulence due to in vitro passaging. It is critical to verify virulence of parental strains before genetic manipulations are undertaken and comparisons are made.     

Lipoarabinomannan mannose caps do not affect mycobacterial virulence or the induction of protective immunity in experimental animal models of infection and have minimal impact on in vitro inflammatory responses

Mannose‐capped lipoarabinomannan (ManLAM) is considered an important virulence factor of Mycobacterium tuberculosis. However, while mannose caps have been reported to be responsible for various immunosuppressive activities of ManLAMobserved in vitro, there is conflicting evidence about their contribution to mycobacterial virulence in vivo. Therefore, we used Mycobacterium bovis BCG and M. tuberculosis mutants that lack the mannose cap of LAM to assess the role of ManLAM in the interaction of mycobacteria with the host cells, to evaluate vaccine‐induced protection and to determine its importance in M. tuberculosis virulence. Deletion of the mannose cap did not affect BCG survival and replication in macrophages, although the capless mutant induced a somewhat higher production of TNF. In dendritic cells, the capless mutant was able to induce the upregulation of co‐stimulatory molecules and the only difference we detected was the secretion of slightly higher amounts of IL‐10 as compared to the wild type strain. In mice, capless BCG survived equally well and induced an immune response similar to the parental strain. Furthermore, the efficacy of vaccination against a M. tuberculosis challenge in low‐dose aerosol infection models in mice and guinea pigs was not affected by the absence of the mannose caps in the BCG. Finally, the lack of the mannose cap in M. tuberculosis did not affect its virulence in mice nor its interaction with macrophages in vitro. Thus, these results do not support a major role for the mannose caps of LAM in determining mycobacterial virulence and immunogenicity in vivo in experimental animal models of infection, possibly because of redundancy of function.     

GSMN-TB: a web-based genome-scale network model of <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis>metabolism

Background  

An impediment to the rational development of novel drugs against tuberculosis (TB) is a general paucity of knowledge concerning the metabolism of Mycobacterium tuberculosis, particularly during infection. Constraint-based modeling provides a novel approach to investigating microbial metabolism but has not yet been applied to genome-scale modeling of M. tuberculosis.     

Bacterial Thymidine Kinase as a Non-Invasive Imaging Reporter for Mycobacterium tuberculosis in Live Animals

Background

Bacteria can be selectively imaged in experimentally-infected animals using exogenously administered 1-(2′deoxy-2′-fluoro-β-D-arabinofuranosyl)-5-[¹²⁵I]-iodouracil ([¹²⁵I]-FIAU), a nucleoside analog substrate for bacterial thymidine kinase (TK). Our goal was to use this reporter and develop non-invasive methods to detect and localize Mycobacterium tuberculosis.

Methodology/Principal Findings

We engineered a M. tuberculosis strain with chromosomally integrated bacterial TK under the control of hsp60 - a strong constitutive mycobacterial promoter. [¹²⁵I]FIAU uptake, antimicrobial susceptibilities and in vivo growth characteristics were evaluated for this strain. Using single photon emission computed tomography (SPECT), M. tuberculosis P_hsp60 TK strain was evaluated in experimentally-infected BALB/c and C3HeB/FeJ mice using the thigh inoculation or low-dose aerosol infection models. M. tuberculosis P_hsp60 TK strain actively accumulated [¹²⁵I]FIAU in vitro. Growth characteristics of the TK strain and susceptibility to common anti-tuberculous drugs were similar to the wild-type parent strain. M. tuberculosis P_hsp60 TK strain was stable in vivo and SPECT imaging could detect and localize this strain in both animal models tested.

Conclusion

We have developed a novel tool for non-invasive assessment of M. tuberculosis in live experimentally-infected animals. This tool will allow real-time pathogenesis studies in animal models of TB and has the potential to simplify preclinical studies and accelerate TB research.     

Expression of Lactobacillus brevis IOEB 9809 tyrosine decarboxylase and agmatine deiminase genes in wine correlates with substrate availability

Aims: Lactobacillus brevis IOEB 9809 is able to produce both tyramine and putrescine via tyrosine decarboxylase and agmatine deiminase enzymes, respectively, when cultured on synthetic media. The aims of this study were to assess the expression of L. brevis IOEB 9809 tdc and aguA1 genes, during wine fermentation and to evaluate the effect of substrate availability and pH on tdc and aguA1 expression, as well as on biogenic amine production and L. brevis viability. Methods and Results: The relative expression of L. brevis IOEB 9809 tdc and aguA1 genes was analysed in wine by quantitative real‐time RT‐PCR (qRT‐PCR) during a period of incubation of 30 days. Cell viability, pH values, putrescine and tyramine concentration were monitored throughout the experiments. Conclusions: The wine trials indicated that L. brevis IOEB 9809 is able to produce both tyramine and putrescine during wine fermentation. Increased cell viability was also observed in wine supplemented with tyrosine or agmatine. qRT‐PCR analysis suggests a strong influence of substrate availability on the expression of genes coding for tyrosine decarboxylase and agmatine deiminase in L. brevis IOEB 9809. Less evident is the relationship between putrescine and tyramine production and tolerance to wine pH. Significance and Impact of Study: To our knowledge, this study represents the first assessment of relative expression of L. brevis IOEB 9809 genes involved in biogenic amine production in wine. Furthermore, an effect of biogenic amine production on viability of L. brevis during wine fermentation was established.     

Effect of ante- and postmortem hide clipping on the microbiological quality and safety and ultimate pH value of beef carcasses in an EC-approved abattoir

Aims:  Effect of ante- and postmortem hide clipping on the microbiological quality of beef carcasses. Methods and Results:  Bovine carcasses (362) were tested for indicator micro-organisms and the presence of pathogens. Prior to slaughter, hide cleanliness of each animal was categorized on a scale of 1–5 (clean to dirty). Lowest mean aerobic colony counts (ACC) (log₁₀ 3·0 CFU cm⁻²) came from carcasses where clipping had been performed in lairage, antemortem. ACC from animals clipped online (log₁₀ 3·2 CFU cm⁻²) were significantly higher (P < 0·05) than those clipped in lairage, but comparable to those carcasses from Category 1 and 2 animals. There were no significant differences in the detection of pathogens from any of the carcass groups. Ultimate pH values for carcasses from Category 3 and 4 animals showed clipping animals in lairage, as opposed to online, resulted in a small, but significant increase (P < 0·05) in pH value (mean pH 5·66 and 5·59, respectively). Conclusions:  Hide clipping does not adversely affect microbiological quality of carcasses, although higher ultimate pH values indicate increases in antemortem stress. Significance and Impact of the Study:  Hide clipping carcasses both ante- and postmortem appears to be an effective intervention to minimize transfer of hide microflora to carcasses during slaughtering operations. Online clipping offers advantages for animal welfare and improves safety for operatives.     

Comparison of Five Bacteriophages as Models for Viral Aerosol Studies

Bacteriophages are perceived to be good models for the study of airborne viruses because they are safe to use, some of them display structural features similar to those of human and animal viruses, and they are relatively easy to produce in large quantities. Yet, only a few studies have investigated them as models. It has previously been demonstrated that aerosolization, environmental conditions, and sampling conditions affect viral infectivity, but viral infectivity is virus dependent. Thus, several virus models are likely needed to study their general behavior in aerosols. The aim of this study was to compare the effects of aerosolization and sampling on the infectivity of five tail-less bacteriophages and two pathogenic viruses: MS2 (a single-stranded RNA [ssRNA] phage of the Leviviridae family), Φ6 (a segmented double-stranded RNA [dsRNA] phage of the Cystoviridae family), ΦX174 (a single-stranded DNA [ssDNA] phage of the Microviridae family), PM2 (a double-stranded DNA [dsDNA] phage of the Corticoviridae family), PR772 (a dsDNA phage of the Tectiviridae family), human influenza A virus H1N1 (an ssRNA virus of the Orthomyxoviridae family), and the poultry virus Newcastle disease virus (NDV; an ssRNA virus of the Paramyxoviridae family). Three nebulizers and two nebulization salt buffers (with or without organic fluid) were tested, as were two aerosol sampling devices, a liquid cyclone (SKC BioSampler) and a dry cyclone (National Institute for Occupational Safety and Health two-stage cyclone bioaerosol sampler). The presence of viruses in collected air samples was detected by culture and quantitative PCR (qPCR). Our results showed that these selected five phages behave differently when aerosolized and sampled. RNA phage MS2 and ssDNA phage ΦX174 were the most resistant to aerosolization and sampling. The presence of organic fluid in the nebulization buffer protected phages PR772 and Φ6 throughout the aerosolization and sampling with dry cyclones. In this experimental setup, the behavior of the influenza virus resembled that of phages PR772 and Φ6, while the behavior of NDV was closer to that of phages MS2 and ΦX174. These results provide critical information for the selection of appropriate phage models to mimic the behavior of specific human and animal viruses in aerosols.     

Polymorphisms of 20 regulatory proteins between Mycobacterium tuberculosis and Mycobacterium bovis

Mycobacterium tuberculosis and Mycobacterium bovis are responsible for tuberculosis in humans and animals, respectively. Both species are closely related and belong to the Mycobacterium tuberculosis complex (MTC). M. tuberculosis is the most ancient species from which M. bovis and other members of the MTC evolved. The genome of M. bovis is over >99.95% identical to that of M. tuberculosis but with seven deletions ranging in size from 1 to 12.7 kb. In addition, 1200 single nucleotide mutations in coding regions distinguish M. bovis from M. tuberculosis. In the present study, we assessed 75 M. tuberculosis genomes and 23 M. bovis genomes to identify non‐synonymous mutations in 202 coding sequences of regulatory genes between both species. We identified species‐specific variants in 20 regulatory proteins and confirmed differential expression of hypoxia‐related genes between M. bovis and M. tuberculosis.     

Upregulation of a histone-like protein in dormant Mycobacterium smegmatis

The aerobic saprophyte Mycobacterium smegmatis, like its pathogenic counterpart M. tuberculosis, has the ability to adapt to anaerobiosis by shifting down to a dormant state. Here, we report the identification and molecular genetic characterisation of the first dormancy-induced protein in M. smegmatis. Comparative SDS-polyacrylamide gel electrophoresis of protein extracts of aerobically growing and dormant anaerobic M. smegmatis cultures revealed the upregulation of a 27-kDa protein in the dormant state. Peptide sequencing showed that the induced protein is a homologue of the histone-like protein Hlp, predicted by the M. tuberculosis genome project. The corresponding hlp gene was cloned from M. smegmatis and sequenced. Disruption of the hlp gene eliminated the histone-like protein but did not affect the viability of the dormant culture. Received: 3 June 1998 / Accepted: 22 September 1998     

A 38-kDa Antigen of Mycobacterium tuberculosis Predominantly Induces the Secretion of Interleukin-2, Interferon-gamma and IgG2a Antibodies

In the present study, mice of 3 different haplotypes (H-2d, H-2k and H-2b) were sensitized subcutaneously with heat-killed H37Ra or 38-kDa antigen of Mycobacterium tuberculosis. Lymphocytes obtained from immunized animals were challenged in vitro with 38-kDa antigen in both cases. The dominant pattern of Th1-like lymphokines (IL-2 and IFN-gamma) and preferential production of 38-kDa specific IgG2a-type antibody were observed. It was noted that 38-kDa antigen was recognized permissively by all 3 strains of mice used in the present study. It was interesting to note that C3H/HeJ mice, which express BCG-resistant alleles showed a higher level of proliferative as well as cytokine response as compared to BALB/c and C57BL/6 mice, which bear BCG-susceptible alleles. These results suggest that not only in recall responses but also during the induction as well as expression phase of the immune response mediated by 38-kDa antigen of M. tuberculosis the Th1-like immune response predominates.     

Extension of Bacillus endospore gas dynamic heating studies to multiple species and test conditions

Aims: Shock wave–induced damage to a variety of Bacillus endospore species is studied for a wide range of postshock temperatures and test times in oxidative and non‐oxidative gas environments. Methods and Results: Bacillus atrophaeus and Bacillus subtilis endospores are nebulized into an aqueous aerosol, loaded into the Stanford aerosol shock tube (SAST) and subjected to shock waves of controlled strength. Endospores experience uniform test temperatures between 500 and 1000 K and pressures ranging from 2 to 7 atm, for either a short test time (～2·5 ms) or a relatively long test time (～45 ms). During this process, the bioaerosol is observed using in situ laser absorption and scattering diagnostics. Additionally, shock‐treated samples are extracted for ex situ analysis including viability plating and flow cytometry. For short test times, results are consistent with previous studies; all endospore species begin to lose the ability to form colonies when shock‐heated to temperatures above 500 K, while significant breakdown in morphology is observed for postshock temperatures above 700 K. Oxidative bath gases did not affect viability losses or morphological breakdown rates. Experiments with extended postshock test time showed increased viability loss with minimal morphological damage for shocks between 600 and 700 K. Conclusions: Genetic differences between B. subtilis and B. atrophaeus endospores do not confer noticeable gains in resistance to shock heating. Oxidative environments do not exacerbate shock‐induced damage to endospores. Extended test time experiments reinforce our hypothesis that a temperature/time‐dependent inactivation mechanism that does not involve morphological breakdown exists at low‐to‐moderate postshock temperatures. Significance and Impact of the Study: The methodology and experiments described in this paper extend the study of the interactions of endospores with shock/blast waves to new species and environmental conditions.     

Cell viability and immunostimulating and protective capacities of Bifidobacterium longum 51A are differentially affected by technological variables in fermented milks

Aim: To investigate the cell viability of Bifidobacterium longum 5^1A in fermented milks and to study its immunostimulating and protective capacity against Salmonella enterica ssp. enterica serovar Typhimurium infection in mice. Methods and Results: Bifidobacterium longum 5^1A was added to milk fermented with different yoghurt starter cultures, before or after fermentation, and viability was monitored during storage (5°C, 28 days). Resistance to simulated gastric acid digestion was assessed. Fermented milks were orally administered to mice for 10 days followed by oral infection with Salmonella Typhimurium. The number of IgA+ cells in the small and large intestine was determined before infection. Survival to infection was monitored for 20 days. Bifidobacterium longum 5^1A lost viability during storage, but the product containing it was effective for the induction of IgA+ cells proliferation in the gut and for the protection of mice against Salm. Typhimurium infection. Conclusions: Cell viability of Bif. longum 5^1A in fermented milks along storage did not condition the capacity of the strain to enhance the number of IgA+ cells in the gut and to protect mice against Salmonella infection. Significance and Impact of the Study: The uncoupling of cell viability and functionality demonstrated that, in certain cases, nonviable cells can also exert positive effects.     

Effect of recombinant Rv1009 protein on promoting the growth of Mycobacterium tuberculosis

Aims: To determine whether resuscitation-promoting factor (RPF) from Mycobacterium tuberculosis can promote mycobacterial growth and shorten culture time. Method and Results: We cloned, expressed and purified an RPF from M. tuberculosis, Rv1009 protein and subsequently studied the biological activity of the recombinant Rv1009 (rRv1009) in liquid and on solid media. Our results indicate that the molecular weight of rRv1009 protein expressed in Escherichia coli BL21 was approximately 39 kDa. At picomolar and micromolar concentrations, rRv1009 protein could increase the optical density of freeze-dried Mycobacterium bovis BCG three to fivefold in Middlebrook 7H9 medium, stimulate the growth of viable mycobacteria on solid medium, and shorten positive growth detection time of a small number of M. tuberculosis in BACTEC 960 medium. Conclusions: The rRv1009 could promote proliferation of mycobacteria. It may be useful for culture of mycobacteria presented in clinical samples. Significance and Impact of the Study: rRv1009 protein can be used as a growth-promoting reagent of mycobacteria in the medium to shorten the time of culture.     

Involvement of the autophagy pathway in trafficking of Mycobacterium tuberculosis bacilli through cultured human type II epithelial cells

Interactions between Mycobacterium tuberculosis bacilli and alveolar macrophages have been extensively characterized, while similar analyses in epithelial cells have not been performed. In this study, we microscopically examined endosomal trafficking of M. tuberculosis strain Erdman in A549 cells, a human type II pneumocyte cell line. Immuno‐electron microscopic (IEM) analyses indicate that M. tuberculosis bacilli are internalized to a compartment labelled first with Rab5 and then with Rab7 small GTPase proteins. This suggests that, unlike macrophages, M. tuberculosis bacilli traffic to late endosomes in epithelial cells. However, fusion of lysosomes with the bacteria‐containing compartment appears to be inhibited, as illustrated by IEM studies employing LAMP‐2 and cathepsin‐L antibodies. Examination by transmission electron microscopy and IEM revealed M. tuberculosis‐containing compartments surrounded by double membranes and labelled with antibodies against the autophagy marker Lc3, providing evidence for involvement and intersection of the autophagy and endosomal pathways. Interestingly, inhibition of the autophagy pathway using 3‐methyladenine improved host cell viability and decreased numbers of viable intracellular bacteria recovered after 72 h post infection. Collectively, these datasuggest that trafficking patterns for M. tuberculosis bacilli in alveolar epithelial cells differ from macrophages, and that autophagy is involved this process.     

Aptamer inhibits <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> (H37Rv) invasion of macrophage

There is an urgent need to develop new anti-tuberculosis drugs due to the rising tendency in tuberculosis (TB) around the world. It is known that Mycobacterium tuberculosis (M. tuberculosis) generally infects mammalian host via aerosol route. The pathogenic process has been fully studied that it can initially invade alveolar macrophage, then established stable residence within those phagocytic cells, suggesting that one of the possible ways to prevent this pathogen is to inhibit its invasion and growth in the macrophage. Aptamers from SELEX (Systematic Evolution of Ligands by Exponential Enrichment) have been used to rival virulent M. tuberculosis (H37Rv) in our previous work, and the materials to which aptamers bound were proved to be some outer membrane proteins of H37Rv. In the present study, the interaction between M. tuberculosis and macrophage in the presence of aptamers was investigated in more details. The results suggested that the selective aptamers significantly inhibited H37Rv invasion of macrophage in vitro, and the effect correspond to the binding affinity of these aptamers to H37Rv. The values of equilibrium dissociation constant (Kd) was calculated by flow cytometry, all in the nanomolar range, showed much higher affinity to H37Rv than M. bovis Bacillus Guerin (BCG). Moreover, the aptamer-treated H37Rv can stimulate IFN-γ, IL-15 and IL-17 secretion of macrophages compared with H37Rv (no treated). In summary, our data indicated that the NK2 aptamer not only acted as anti-tuberculosis agent by inhibiting virulent M. tuberculosis (H37Rv) invasion of macrophage, but also might be used as molecular probe for exploring the interaction between the outer membrane of M. tuberculosis and macrophage.     

Revisiting Host Preference in the Mycobacterium tuberculosis Complex: Experimental Infection Shows M. tuberculosis H37Rv to Be Avirulent in Cattle

Experiments in the late 19th century sought to define the host specificity of the causative agents of tuberculosis in mammals. Mycobacterium tuberculosis, the human tubercle bacillus, was independently shown by Smith, Koch, and von Behring to be avirulent in cattle. This finding was erroneously used by Koch to argue the converse, namely that Mycobacterium bovis, the agent of bovine tuberculosis, was avirulent for man, a view that was subsequently discredited. However, reports in the literature of M. tuberculosis isolation from cattle with tuberculoid lesions suggests that the virulence of M. tuberculosis for cattle needs to be readdressed. We used an experimental bovine infection model to test the virulence of well-characterized strains of M. tuberculosis and M. bovis in cattle, choosing the genome-sequenced strains M. tuberculosis H37Rv and M. bovis 2122/97. Cattle were infected with approximately 10⁶ CFU of M. tuberculosis H37Rv or M. bovis 2122/97, and sacrificed 17 weeks post-infection. IFN-γ and tuberculin skin tests indicated that both M. bovis 2122 and M. tuberculosis H37Rv were equally infective and triggered strong cell-mediated immune responses, albeit with some indication of differential antigen-specific responses. Postmortem examination revealed that while M. bovis 2122/97–infected animals all showed clear pathology indicative of bovine tuberculosis, the M. tuberculosis–infected animals showed no pathology. Culturing of infected tissues revealed that M. tuberculosis was able to persist in the majority of animals, albeit at relatively low bacillary loads. In revisiting the early work on host preference across the M. tuberculosis complex, we have shown M. tuberculosis H37Rv is avirulent for cattle, and propose that the immune status of the animal, or genotype of the infecting bacillus, may have significant bearing on the virulence of a strain for cattle. This work will serve as a baseline for future studies into the genetic basis of host preference, and in particular the molecular basis of virulence in M. bovis.     

Mycobacterium tuberculosis activates the DNA-dependent cytosolic surveillance pathway within macrophages

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Highlights? M. tuberculosis permeabilizes phagosomes and activates cytosolic signaling pathways ? Host cytoplasmic DNA receptors sense M. tuberculosis extracellular DNA ? DNA recognition activates the STING/TBK1/IRF3 pathway ? Cytosolic sensing promotes M. tuberculosis infection