Spatially distinct and metabolically active membrane domain in mycobacteria.

Protected from host immune attack and antibiotic penetration by their unique cell envelope, mycobacterial pathogens cause devastating human diseases such as tuberculosis. Seamless coordination of cell growth with cell envelope elongation at the pole maintains this barrier. Unraveling this spatiotemporal regulation is a potential strategy for controlling mycobacterial infections. Our biochemical analysis previously revealed two functionally distinct membrane fractions in Mycobacterium smegmatis cell lysates: plasma membrane tightly associated with the cell wall (PM-CW) and a distinct fraction of pure membrane free of cell wall components (PMf). To provide further insight into the functions of these membrane fractions, we took the approach of comparative proteomics and identified more than 300 proteins specifically associated with the PMf, including essential enzymes involved in cell envelope synthesis such as a mannosyltransferase, Ppm1, and a galactosyltransferase, GlfT2. Furthermore, comparative lipidomics revealed the distinct lipid composition of the PMf, with specific association of key cell envelope biosynthetic precursors. Live-imaging fluorescence microscopy visualized the PMf as patches of membrane spatially distinct from the PM-CW and notably enriched in the pole of the growing cells. Taken together, our study provides the basis for assigning the PMf as a spatiotemporally distinct and metabolically active membrane domain involved in cell envelope biogenesis.

Potential role for ESAT6 in dissemination of M. tuberculosis via human lung epithelial cells.

ESAT6 has recently been demonstrated to cause haemolysis and macrophage lysis. Our studies demonstrate that ESAT6 causes cytolysis of type 1 and type 2 pneumocytes. Both types of pneumocytes express membrane laminin, and ESAT6 exhibits dose-dependent binding to both cell types and to purified human laminin. While minimal ESAT6 was detected on the surface of Mycobacterium tuberculosis grown in vitro, exogenously provided ESAT6 specifically associated with the bacterial cell surface, and the bacterium-associated ESAT6 retained its cytolytic ability. esat6 transcripts were upregulated approximately 4- to approximately 13-fold in bacteria replicating in type 1 cells, and approximately 3- to approximately 5 fold in type 2 cells. In vivo, laminin is primarily concentrated at the basolateral surface of pneumocytes where they rest on the basement membrane, which is composed primarily of laminin and collagen. The upregulation of esat6 transcripts in bacteria replicating in pneumocytes, the specific association of ESAT6 with the bacterial surface, the binding of ESAT6 to laminin and the lysis of pneumocytes by free and bacterium-associated ESAT6 together suggest a scenario wherein Mycobacterium tuberculosis replicating in pneumocytes may utilize surface ESAT6 to anchor onto the basolateral laminin-expressing surface of the pneumocytes, and damage the cells and the basement membrane to directly disseminate through the alveolar wall.

Mycolic acid modification by the mmaA4 gene of M. tuberculosis modulates IL-12 production.

Mycobacterium tuberculosis has evolved many strategies to evade elimination by the host immune system, including the selective repression of macrophage IL-12p40 production. To identify the M. tuberculosis genes responsible for this aspect of immune evasion, we used a macrophage cell line expressing a reporter for IL-12p40 transcription to screen a transposon library of M. tuberculosis for mutants that lacked this function. This approach led to the identification of the mmaA4 gene, which encodes a methyl transferase required for introducing the distal oxygen-containing modifications of mycolic acids, as a key locus involved in the repression of IL-12p40. Mutants in which mmaA4 (hma) was inactivated stimulated macrophages to produce significantly more IL-12p40 and TNF-alpha than wild-type M. tuberculosis and were attenuated for virulence. This attenuation was not seen in IL-12p40-deficient mice, consistent with a direct linkage between enhanced stimulation of IL-12p40 by the mutant and its reduced virulence. Treatment of macrophages with trehalose dimycolate (TDM) purified from the DeltammaA4 mutant stimulated increased IL-12p40, similar to the increase observed from DeltammaA4 mutant-infected macrophages. In contrast, purified TDM isolated from wild-type M. tuberculosis inhibited production of IL-12p40 by macrophages. These findings strongly suggest that M. tuberculosis has evolved mmaA4-derived mycolic acids, including those incorporated into TDM to manipulate IL-12-mediated immunity and virulence.

Growth of Mycobacterium tuberculosis biofilms containing free mycolic acids and harbouring drug-tolerant bacteria.

Successful treatment of human tuberculosis requires 6-9 months' therapy with multiple antibiotics. Incomplete clearance of tubercle bacilli frequently results in disease relapse, presumably as a result of reactivation of persistent drug-tolerant Mycobacterium tuberculosis cells, although the nature and location of these persisters are not known. In other pathogens, antibiotic tolerance is often associated with the formation of biofilms--organized communities of surface-attached cells--but physiologically and genetically defined M. tuberculosis biofilms have not been described. Here, we show that M. tuberculosis forms biofilms with specific environmental and genetic requirements distinct from those for planktonic growth, which contain an extracellular matrix rich in free mycolic acids, and harbour an important drug-tolerant population that persist despite exposure to high levels of antibiotics.

Mycobacterium tuberculosis nuoG is a virulence gene that inhibits apoptosis of infected host cells.

The survival and persistence of Mycobacterium tuberculosis depends on its capacity to manipulate multiple host defense pathways, including the ability to actively inhibit the death by apoptosis of infected host cells. The genetic basis for this anti-apoptotic activity and its implication for mycobacterial virulence have not been demonstrated or elucidated. Using a novel gain-of-function genetic screen, we demonstrated that inhibition of infection-induced apoptosis of macrophages is controlled by multiple genetic loci in M. tuberculosis. Characterization of one of these loci in detail revealed that the anti-apoptosis activity was attributable to the type I NADH-dehydrogenase of M. tuberculosis, and was mainly due to the subunit of this multicomponent complex encoded by the nuoG gene. Expression of M. tuberculosis nuoG in nonpathogenic mycobacteria endowed them with the ability to inhibit apoptosis of infected human or mouse macrophages, and increased their virulence in a SCID mouse model. Conversely, deletion of nuoG in M. tuberculosis ablated its ability to inhibit macrophage apoptosis and significantly reduced its virulence in mice. These results identify a key component of the genetic basis for an important virulence trait of M. tuberculosis and support a direct causal relationship between virulence of pathogenic mycobacteria and their ability to inhibit macrophage apoptosis.

Use of a Mycoplasma hyopneumoniae nested polymerase chain reaction test to determine the optimal sampling sites in swine.

A number of polymerase chain reaction (PCR)-based diagnostic tests have been developed for Mycoplasma hyopneumoniae, including one from this research group. This report presents further development, optimization, and standardization of a nested PCR test. Detection sensitivity was 1 fg of M. hyopneumoniae chromosomal DNA (approximately 1 organism). This exceeded the sensitivity of or compared favorably with other published PCR tests. Polymerase chain reaction primers to porcine beta2-microglobulin were included as internal controls for amplifiable chromosomal DNA from porcine samples. To standardize the test, a number of samples from experimentally infected pigs, including nasal, tonsil, tracheobronchial swabs, lung tissue, bronchial alveolar lavage (BAL) fluid, and tracheobronchial brush samples, were examined by PCR. Samples obtained from BAL fluid and tracheobronchial sites were most predictive of infection, whereas nasal swabs and lung tissue were not reliable indicators of experimentally induced infection. In conclusion, the nested PCR developed for this study was found to be a highly sensitive and specific diagnostic tool for M. hyopneumoniae, but the enhanced sensitivity may be unnecessary if the proper sites are sampled.

ESX1-dependent fractalkine mediates chemotaxis and Mycobacterium tuberculosis infection in humans.

Mycobacterium tuberculosis-induced cellular aggregation is essential for granuloma formation and may assist establishment and early spread of M. tuberculosis infection. The M. tuberculosis ESX1 mutant, which has a non-functional type VII secretion system, induced significantly less production of the host macrophage-derived chemokine fractalkine (CX3CL1). Upon infection of human macrophages ESX1-dependent fractalkine production mediated selective recruitment of CD11b+ monocytic cells and increased infection of neighbouring cells consistent with early local spread of infection. Fractalkine levels were raised in vivo at tuberculous disease sites in humans and were significantly associated with increased CD11b+ monocytic cellular recruitment and extent of granulomatous disease. These findings suggest a novel fractalkine-dependent ESX1-mediated mechanism in early tuberculous disease pathogenesis in humans. Modulation of M. tuberculosis-mediated fractalkine induction may represent a potential treatment option in the future, perhaps allowing us to switch off a key mechanism required by the pathogen to spread between cells.

Specialized transduction designed for precise high-throughput unmarked deletions in Mycobacterium tuberculosis.

UNLABELLED: Specialized transduction has proven to be useful for generating deletion mutants in most mycobacteria, including virulent Mycobacterium tuberculosis. We have improved this system by developing (i) a single-step strategy for the construction of allelic exchange substrates (AES), (ii) a temperature-sensitive shuttle phasmid with a greater cloning capacity than phAE87, and (iii) bacteriophage-mediated transient expression of site-specific recombinase to precisely excise antibiotic markers. The methods ameliorate rate-limiting steps in strain construction in these difficult-to-manipulate bacteria. The new methods for strain construction were demonstrated to generalize to all classes of genes and chromosomal loci by generating more than 100 targeted single- or multiple-deletion substitutions. These improved methods pave the way for the generation of a complete ordered library of M. tuberculosis null strains, where each strain is deleted for a single defined open reading frame in M. tuberculosis. IMPORTANCE: This work reports major advances in the methods of genetics applicable to all mycobacteria, including but not limited to virulent M. tuberculosis, which would facilitate comparative genomics to identify drug targets, genetic validation of proposed pathways, and development of an effective vaccine. This study presents all the new methods developed and the improvements to existing methods in an integrated way. The work presented in this study could increase the pace of mycobacterial genetics significantly and will immediately be of wide use. These new methods are transformative and allow for the undertaking of construction of what has been one of the most fruitful resources in model systems: a comprehensive, ordered library set of the strains, each of which is deleted for a single defined open reading frame.

Overexpression of EPH receptor B2 in malignant mesothelioma correlates with oncogenic behavior.

INTRODUCTION: Malignant pleural mesothelioma (MM) is an aggressive asbestos-associated malignancy with limited therapeutic options. This study describes the overexpression of Ephrin B2 receptor (EPHB2) in MM cell lines and tumors, and the effect of its manipulation on proliferative and invasive qualities of the disease. METHODS: Using expression arrays, we investigated EPHB2 in MM tumors compared with normal mesothelium. EPHB2 and downstream target expression were evaluated using reverse-transcriptase polymerase chain reaction and immunoblotting methods. The biological significance of EPHB2 in MM was evaluated using in vitro functional assays with and without targeting by EPHB2-short hairpin RNA or blocking peptide in two mesothelioma cell lines, HP-1 and H2595. RESULTS: EPHB2 is overexpressed in all MM cell lines, but not in benign mesothelial cells, and is significantly elevated in MM tumor tissue compared with matched normal peritoneum. Targeted knockdown of EPHB2 in HP-1 and H2595 cell lines reduced its expression and that of EPHB2 downstream targets such as matrix metalloproteinase (MMP-2) and vascular endothelial growth factor, whereas caspase 2 and caspase 8 had increased expression. Inhibition of EPHB2 resulted in a significant decrease in scratch closure (1.25-fold-1.8-fold), proliferation (1.5-fold), and invasion (1.7-fold-1.8-fold) compared with the controls. Most notably, however, EPHB2 silencing resulted in a significant increase in apoptotic proteins and activity. CONCLUSION: EPHB2 seems to play an important role in MM pathogenesis and these findings indicate that EPHB2 could serve as a potential novel therapeutic target for treatment of the disease.

Einstein Contained Aerosol Pulmonizer (ECAP): Improved Biosafety for Multi-Drug Resistant (MDR) and Extensively Drug Resistant (XDR) Mycobacterium tuberculosis Aerosol Infection Studies.

A new apparatus enhances the biosafety of containment (biosafety level 3 [BSL-3]) and provides experimental reproducibility for aerosol infection experiments with MDR and XDR Mycobacterium tuberculosis. The methods are generally applicable to the study of airborne pathogens.

A recombinant Mycobacterium smegmatis induces potent bactericidal immunity against Mycobacterium tuberculosis.

We report the involvement of an evolutionarily conserved set of mycobacterial genes, the esx-3 region, in evasion of bacterial killing by innate immunity. Whereas high-dose intravenous infections of mice with the rapidly growing mycobacterial species Mycobacterium smegmatis bearing an intact esx-3 locus were rapidly lethal, infection with an M. smegmatis Δesx-3 mutant (here designated as the IKE strain) was controlled and cleared by a MyD88-dependent bactericidal immune response. Introduction of the orthologous Mycobacterium tuberculosis esx-3 genes into the IKE strain resulted in a strain, designated IKEPLUS, that remained susceptible to innate immune killing and was highly attenuated in mice but had a marked ability to stimulate bactericidal immunity against challenge with virulent M. tuberculosis. Analysis of these adaptive immune responses indicated that the highly protective bactericidal immunity elicited by IKEPLUS was dependent on CD4(+) memory T cells and involved a distinct shift in the pattern of cytokine responses by CD4(+) cells. Our results establish a role for the esx-3 locus in promoting mycobacterial virulence and also identify the IKE strain as a potentially powerful candidate vaccine vector for eliciting protective immunity to M. tuberculosis.

Construction of an unmarked recombinant BCG expressing a pertussis antigen by auxotrophic complementation: protection against Bordetella pertussis challenge in neonates.

Mycobacterium bovis BCG has long been investigated as a candidate for heterologous antigen presentation. We have previously described an rBCG-Pertussis that confers protection against challenge with Bordetella pertussis in neonate and adult mice. In order to obtain stable expression in vivo, we constructed an unmarked BCG lysine auxotrophic and a complementation vector containing the lysine and the genetically detoxified S1 pertussis toxin genes, both under control of the same promoter. Complemented BCG-Delta lysine growth and expression of the pertussis antigen were stable, without the use of an antibiotic marker. Our results show that the complemented rBCG-Delta lysA-S1PT-lysA(+)(kan(-)), which is now suitable to be evaluated in clinical trials, maintains similar characteristics of the original rBCG-pNL71S1PT strain, such as the antigen expression level, cellular immune response and protection against the same model challenge in neonatal-immunized mice.

Efficacy and immunogenicity of Mycobacterium bovis DeltaRD1 against aerosol M. bovis infection in neonatal calves.

An attenuated Mycobacterium bovisRD1 deletion (DeltaRD1) mutant of the Ravenel strain was constructed, characterized, and sequenced. This M. bovis DeltaRD1 vaccine strain administered to calves at 2 weeks of age provided similar efficacy as M. bovis bacillus Calmette Guerin (BCG) against low dose, aerosol challenge with virulent M. bovis at 3.5 months of age. Approximately 4.5 months after challenge, both DeltaRD1- and BCG-vaccinates had reduced tuberculosis (TB)-associated pathology in lungs and lung-associated lymph nodes and M. bovis colonization of tracheobronchial lymph nodes as compared to non-vaccinates. Mean central memory responses elicited by either DeltaRD1 or BCG prior to challenge correlated with reduced pathology and bacterial colonization. Neither DeltaRD1 or BCG elicited IFN-gamma responses to rESAT-6:CFP-10 prior to challenge, an emerging tool for modern TB surveillance programs. The DeltaRD1 strain may prove useful for bovine TB vaccine programs, particularly if additional mutations are included to improve safety and immunogenicity.

Efficacy and safety of live attenuated persistent and rapidly cleared Mycobacterium tuberculosis vaccine candidates in non-human primates.

Tuberculosis (TB) remains a global health burden for which safe vaccines are needed. BCG has limitations as a TB vaccine so we have focused on live attenuated Mycobacterium tuberculosis mutants as vaccine candidates. Prior to human studies, however, it is necessary to demonstrate safety in non-human primates (NHP). In this study, we evaluate the safety and efficacy of two live attenuated M. tuberculosis double deletion vaccine strains mc(2)6020 (DeltalysA DeltapanCD) and mc(2)6030 (DeltaRD1 DeltapanCD) in cynomolgus macaques. In murine models, mc(2)6020 is rapidly cleared while mc(2)6030 persists. Both mc(2)6020 and mc(2)6030 were safe and well tolerated in cynomolgus macaques. Following a high-dose intrabronchial challenge with virulent M. tuberculosis, mc(2)6020-vaccinates were afforded a level of protection intermediate between that elicited by BCG vaccination and no vaccination. BCG vaccinates had reduced tuberculosis-associated pathology and improved clinical scores as compared to saline and mc(2)6030 vaccinates, but survival did not differ among the groups.

Sulfite reduction in mycobacteria.

Mycobacterium tuberculosis places an enormous burden on the welfare of humanity. Its ability to grow and its pathogenicity are linked to sulfur metabolism, which is considered a fertile area for the development of antibiotics, particularly because many of the sulfur acquisition steps in the bacterium are not found in the host. Sulfite reduction is one such mycobacterium-specific step and is the central focus of this paper. Sulfite reduction in Mycobacterium smegmatis was investigated using a combination of deletion mutagenesis, metabolite screening, complementation, and enzymology. The initial rate parameters for the purified sulfite reductase from M. tuberculosis were determined under strict anaerobic conditions [k(cat) = 1.0 (+/-0.1) electron consumed per second, and K(m(SO(3)(-2))) = 27 (+/-1) microM], and the enzyme exhibits no detectible turnover of nitrite, which need not be the case in the sulfite/nitrite reductase family. Deletion of sulfite reductase (sirA, originally misannotated nirA) reveals that it is essential for growth on sulfate or sulfite as the sole sulfur source and, further, that the nitrite-reducing activities of the cell are incapable of reducing sulfite at a rate sufficient to allow growth. Like their nitrite reductase counterparts, sulfite reductases require a siroheme cofactor for catalysis. Rv2393 (renamed che1) resides in the sulfur reduction operon and is shown for the first time to encode a ferrochelatase, a catalyst that inserts Fe(2+) into siroheme. Deletion of che1 causes cells to grow slowly on metabolites that require sulfite reductase activity. This slow-growth phenotype was ameliorated by optimizing growth conditions for nitrite assimilation, suggesting that nitrogen and sulfur assimilation overlap at the point of ferrochelatase synthesis and delivery.

Characterization of the protective T-cell response generated in CD4-deficient mice by a live attenuated Mycobacterium tuberculosis vaccine.

The global epidemic of tuberculosis, fuelled by acquired immune-deficiency syndrome, necessitates the development of a safe and effective vaccine. We have constructed a DeltaRD1DeltapanCD mutant of Mycobacterium tuberculosis (mc(2)6030) that undergoes limited replication and is severely attenuated in immunocompromised mice, yet induces significant protection against tuberculosis in wild-type mice and even in mice that completely lack CD4(+) T cells as a result of targeted disruption of their CD4 genes (CD4(-/-) mice). Ex vivo studies of T cells from mc(2)6030-immunized mice showed that these immune cells responded to protein antigens of M. tuberculosis in a major histocompatibility complex (MHC) class II-restricted manner. Antibody depletion experiments showed that antituberculosis protective responses in the lung were not diminished by removal of CD8(+), T-cell receptor gammadelta (TCR-gammadelta(+)) and NK1.1(+) T cells from vaccinated CD4(-/-) mice before challenge, implying that the observed recall and immune effector functions resulting from vaccination of CD4(-/-) mice with mc(2)6030 were attributable to a population of CD4(-) CD8(-) (double-negative) TCR-alphabeta(+), TCR-gammadelta(-), NK1.1(-) T cells. Transfer of highly enriched double-negative TCR-alphabeta(+) T cells from mc(2)6030-immunized CD4(-/-) mice into naive CD4(-/-) mice resulted in significant protection against an aerosol tuberculosis challenge. Enriched pulmonary double-negative T cells transcribed significantly more interferon-gamma and interleukin-2 mRNA than double-negative T cells from naive mice after a tuberculous challenge. These results confirmed previous findings on the potential for a subset of MHC class II-restricted T cells to develop and function without expression of CD4 and suggest novel vaccination strategies to assist in the control of tuberculosis in human immunodeficiency virus-infected humans who have chronic depletion of their CD4(+) T cells.

Mycobacterium tuberculosis DeltaRD1 DeltapanCD: a safe and limited replicating mutant strain that protects immunocompetent and immunocompromised mice against experimental tuberculosis.

The global epidemic of tuberculosis (TB), fueled by the growing HIV pandemic, warrants the development of a safe and effective vaccine against TB. We report the construction and characterization of an unlinked double deletion mutant of Mycobacterium tuberculosis H37Rv that deletes both the primary attenuating mutation of BCG (DeltaRD1) and two genes required for the synthesis of pantothenate (DeltapanCD). The M. tuberculosis DeltaRD1 DeltapanCD (mc(2)6030) mutant undergoes limited replication in mice, and yet is both significantly safer than BCG in immunocompromised mice and also safe in guinea pigs. Additionally, the mc(2)6030 strain does not reactivate in a mouse chemo-immunosuppression model. Importantly, long-lived protective immune responses following immunization with the mc(2)6030 strain prolong the survival of wild type mice, and CD4-deficient mice against an aerosol challenge with virulent M. tuberculosis. Given its overall safety and effectiveness, the mc(2)6030 live attenuated strain should be considered as a human vaccine candidate for protecting both healthy and HIV-infected individuals against TB.

Mycobacteria lacking the RD1 region do not induce necrosis in the lungs of mice lacking interferon-gamma.

The genetic region of difference 1 (RD1) in Mycobacterium tuberculosis has recently been hypothesized to encode for proteins that are cytotoxic to the host cell in nature. We demonstrate here that while M. tuberculosis grew progressively in the lungs of gene disrupted mice (GKO) unable to produce interferon-gamma (IFN-gamma), similar mice infected instead with M. bovis bacillus Calmette-Guérin (BCG) reproducibly exhibited an obvious slowing of the disease after about 20 days. Closer examination of BCG-infected GKO mice showed a florid granulomatous inflammation in the lungs, whereas similar mice infected with M. tuberculosis exhibited wholesale progressive necrosis. In the BCG-infected GKO mice large numbers of activated effector T cells, some strongly positive for the cytokine tumour necrosis factor, as well as activated natural killer cells accumulated in the lungs. To further test the hypothesis that the differences observed were directly associated with the loss of the RD1 region, it was then shown that a mutant of M. tuberculosis lacking RD1 grew progressively in both normal and GKO mice but failed to induce any degree of necrosis in either animal despite reaching similar levels in the lungs. However, when mice were infected with this mutant, in which the RD1 region had been restored by complementation, wholesale necrosis of the lungs again occurred. These data support the hypothesis that proteins encoded in the RD1 region are a major cause of necrosis and contribute significantly to the pathogenesis of the disease.

Generation of mucosal anti-human immunodeficiency virus type 1 T-cell responses by recombinant Mycobacterium smegmatis.

A successful vaccine vector for human immunodeficiency virus type 1 (HIV-1) should induce anti-HIV-1 immune responses at mucosal sites. We have generated recombinant Mycobacterium smegmatis vectors that express the HIV-1 group M consensus envelope protein (Env) as a surface, intracellular, or secreted protein and have tested them in animals for induction of both anti-HIV-1 T-cell and antibody responses. Recombinant M. smegmatis engineered for expression of secreted protein induced optimal T-cell gamma interferon enzyme-linked immunospot assay responses to HIV-1 envelope in the spleen, female reproductive tract, and lungs. Unlike with the induction of T-cell responses, priming and boosting with recombinant M. smegmatis did not induce anti-HIV-1 envelope antibody responses, due primarily to insufficient protein expression of the insert. However, immunization with recombinant M. smegmatis expressing HIV-1 Env was able to prime for an HIV-1 Env protein boost for the induction of anti-HIV-1 antibody responses.

Generation of CD8+ T-cell responses by a recombinant nonpathogenic Mycobacterium smegmatis vaccine vector expressing human immunodeficiency virus type 1 Env.

Because the vaccine vectors currently being evaluated in human populations all have significant limitations in their immunogenicity, novel vaccine strategies are needed for the elicitation of cell-mediated immunity. The nonpathogenic, rapidly growing mycobacterium Mycobacterium smegmatis was engineered as a vector expressing full-length human immunodeficiency virus type 1 (HIV-1) HXBc2 envelope protein. Immunization of mice with recombinant M. smegmatis led to the expansion of major histocompatibility complex class I-restricted HIV-1 epitope-specific CD8(+) T cells that were cytolytic and secreted gamma interferon. Effector and memory T lymphocytes were elicited, and repeated immunization generated a stable central memory pool of virus-specific cells. Importantly, preexisting immunity to Mycobacterium bovis BCG had only a marginal effect on the immunogenicity of recombinant M. smegmatis. This mycobacterium may therefore be a useful vaccine vector.