Sensitive detection of gene expression in mycobacteria under replicating and non-replicating conditions using optimized far-red reporters

Lipid droplet dynamics at early stages of Mycobacterium marinum infection in Dictyostelium

Lipid droplets exist in virtually every cell type, ranging not only from mammals to plants, but also to eukaryotic and prokaryotic unicellular organisms such as Dictyostelium and bacteria. They serve among other roles as energy reservoir that cells consume in times of starvation. Mycobacteria and some other intracellular pathogens hijack these organelles as a nutrient source and to build up their own lipid inclusions. The mechanisms by which host lipid droplets are captured by the pathogenic bacteria are extremely poorly understood. Using the powerful Dictyostelium discoideum/Mycobacterium marinum infection model, we observed that, immediately after their uptake, lipid droplets translocate to the vicinity of the vacuole containing live but not dead mycobacteria. Induction of lipid droplets in Dictyostelium prior to infection resulted in a vast accumulation of neutral lipids and sterols inside the bacterium-containing compartment. Subsequently, under these conditions, mycobacteria accumulated much larger lipid inclusions. Strikingly, the Dictyostelium homologue of perilipin and the murine perilipin 2 surrounded bacteria that had escaped to the cytosol of Dictyostelium or microglial BV-2 cells respectively. Moreover, bacterial growth was inhibited in Dictyostelium plnA knockout cells. In summary, our results provide evidence that mycobacteria actively manipulate the lipid metabolism of the host from very early infection stages.

New indolizines with phenanthroline skeleton: Synthesis, structure, antimycobacterial and anticancer evaluation

We report herein a feasible study concerning the design, synthesis, structure and in vitro antimycobacterial and anticancer activity of two new classes (containing four and five fused rings) of indolizine with phenanthroline skeleton. The preparation is straight and efficient, involving a Huisgen [3+2] dipolar cycloaddition of cycloimmonium ylides to alkynes or alkenes dipolarophiles. The cycloaddition reactions are highly stereo- or regioselective, according with the dipolarophiles nature. The structure of the new compounds was assigned unambiguously, X-ray analysis including. The primary antimycobacterial screening reveals that one of the thirteen tested compounds had a good activity against Mycobacterium tuberculosis H37Rv under aerobic conditions. The antiproliferative evaluation against a NCI 60 human tumor cell line panel, revealed that two indolizine with phenanthroline skeleton exhibit a selective and significant antitumor growth inhibitory activity against Breast Cancer (MCF7 and T-47D) and a slightly moderate activity against some forms of Leukemia, Non-Small Cell Lung Cancer, Renal Cancer and Breast Cancer (MDA-MB-468). The X-ray diffraction study of the indolizines with phenanthroline skeleton prove a flat coplanar structure which, corroborated with their anticancer activity, allow us to suggest that an interaction with DNA (via an intercalation mechanism) would be reasonable.

Fabrication of functional nanofibers through post-nanoparticle functionalization

A facile method is developed to functionalize nanofiber surfaces with nanoparticles (NPs) through dithiocarbamate chemistry. Gold nanoparticles (AuNPs) and quantum dots (QDs) are immobilized on the nanofiber surface. These surfaces provide scaffolds for further supramolecular functionalization, as demonstrated through the Förster resonance energy transfer (FRET) pairing of QD-decorated fibers and fluorescent proteins.

Protein kinase A (PknA) of Mycobacterium tuberculosis is independently activated and is critical for growth in vitro and survival of the pathogen in the host

The essential mycobacterial protein kinases PknA and PknB play crucial roles in modulating cell shape and division. However, the precise in vivo functional aspects of PknA have not been investigated. This study aims to dissect the role of PknA in mediating cell survival in vitro as well as in vivo. We observed aberrant cell shape and severe growth defects when PknA was depleted. Using the mouse infection model, we observe that PknA is essential for survival of the pathogen in the host. Complementation studies affirm the importance of the kinase, juxtamembrane, and transmembrane domains of PknA. Surprisingly, the extracytoplasmic domain is dispensable for cell growth and survival in vitro. We find that phosphorylation of the activation loop at Thr(172) of PknA is critical for bacterial growth. PknB has been previously suggested to be the receptor kinase, which activates multiple kinases, including PknA, by trans-phosphorylating their activation loop residues. Using phospho-specific PknA antibodies and conditional pknB mutant, we find that PknA autophosphorylates its activation loop independent of PknB. Fluorescently tagged PknA and PknB show distinctive distribution patterns within the cell, suggesting that although both kinases are known to modulate cell shape and division, their modes of action are likely to be different. This is supported by our findings that expression of kinase-dead PknA versus kinase-dead PknB in mycobacterial cells leads to different cellular phenotypes. Data indicate that although PknA and PknB are expressed as part of the same operon, they appear to be regulating cellular processes through divergent signaling pathways.

The autophagic machinery ensures nonlytic transmission of mycobacteria

In contrast to mechanisms mediating uptake of intracellular bacterial pathogens, bacterial egress and cell-to-cell transmission are poorly understood. Previously, we showed that the transmission of pathogenic mycobacteria between phagocytic cells also depends on nonlytic ejection through an F-actin based structure, called the ejectosome. How the host cell maintains integrity of its plasma membrane during the ejection process was unknown. Here, we reveal an unexpected function for the autophagic machinery in nonlytic spreading of bacteria. We show that ejecting mycobacteria are escorted by a distinct polar autophagocytic vacuole. If autophagy is impaired, cell-to-cell transmission is inhibited, the host plasma membrane becomes compromised and the host cells die. These findings highlight a previously unidentified, highly ordered interaction between bacteria and the autophagic pathway and might represent the ancient way to ensure nonlytic egress of bacteria.

Mycobacterium tuberculosis H37Rv has a single nucleotide polymorphism in PhoR which affects cell wall hydrophobicity and gene expression

Mycobacterium tuberculosis is a successful pathogen that can adapt to multiple environmental niches. As part of its repertoire of adaptive responses, two-component regulatory systems play a major role in co-ordinating gene expression at the global level. The PhoPR system controls major cellular functions, including respiration, lipid metabolism, the immediate and enduring hypoxic responses, stress responses and persistence. We identified a single nucleotide polymorphism (SNP) found in the sensor kinase (PhoR) of this system between two commonly used strains of M. tuberculosis, H37Rv (PhoR(P152)) and CDC1551 (PhoR(L152)). We constructed an isogenic strain of H37Rv carrying PhoR(L152), as well as strains containing two different copies of the PhoPR locus, to determine the functional consequences of the SNP on phenotypic traits. The previously identified Apr locus was not acid-inducible in H37Rv, although it was in the CDC1551 strain. Surprisingly, the acid-responsive expression was not completely dependent on the PhoR SNP, and the locus remained constitutively expressed even in the isogenic strain H37Rv:PhoR(L152). The pattern of expression in PhoPR merodiploid strains was more complex, with neither allele showing dominance. This suggests that Apr regulation is more complex than previously thought and that additional factors must be responsible for Apr upregulation in response to acid conditions. In contrast, differences we identified in cell hydrophobicity between the two strains were wholly dependent on PhoR, confirming its role as major regulator of cell wall composition. Thus the SNP in the sensor kinase has functional consequences which account for some of the differences between widely used laboratory strains.

Live imaging of Mycobacterium marinum infection in Dictyostelium discoideum

The Dictyostelium discoideum-Mycobacterium marinum host-pathogen system is a recently established and powerful model system for mycobacterial infection. In this chapter, two simple protocols for live imaging of Dictyostelium discoideum infection are described. The first method is used to monitor the dynamics of recruitment of GFP-tagged Dictyostelium discoideum proteins at single time-points corresponding to the main stages of the infection (1.5-72 h post infection). The second method focuses at the early stages of the establishment of an infection (0-3 h post infection). In addition, several procedures to improve the imaging of the bacterium-containing compartment are described. Basic bacterial parameters such as bacterial growth and the recruitment of host proteins to the bacterium-containing compartment can be easily and precisely quantified using macros for ImageJ. These methods can be adapted to monitoring mycobacteria infection in other systems using mammalian cells.

Testing chemical and genetic Modulators in Mycobacterium tuberculosis infected cells using phenotypic assays

Mycobacterium tuberculosis is able to colonize host cells, and it is now well admitted that the intracellular stage of the bacteria contributes to tuberculosis pathogenesis as well as to making it a persistent infection. There is still limited understanding on how the tubercle bacillus colonizes the cell and what are the factors impacting on its intracellular persistence. Recent advances in imaging technique allow rapid quantification of biological objects in complex environments. Furthermore, M. tuberculosis is a microorganism that is particularly genetically tractable and that tolerates the expression of heterologous fluorescent proteins. Thus, the intracellular distribution of M. tuberculosis expressing fluorescent proteins can be easily quantified by the use of confocal microscopy. Here we describe high-content/high-throughput imaging methods that enable tracking the bacillus inside host settings, taking into account the heterogeneity of colonization.

Antibacterial activity of silver and zinc nanoparticles against Vibrio cholerae and enterotoxic Escherichia coli

Vibrio cholerae and enterotoxic Escherichia coli (ETEC) remain two dominant bacterial causes of severe secretory diarrhea and still a significant cause of death, especially in developing countries. In order to investigate new effective and inexpensive therapeutic approaches, we analyzed nanoparticles synthesized by a green approach using corresponding salt (silver or zinc nitrate) with aqueous extract of Caltropis procera fruit or leaves. We characterized the quantity and quality of nanoparticles by UV-visible wavelength scans and nanoparticle tracking analysis. Nanoparticles could be synthesized in reproducible yields of approximately 10(8) particles/ml with mode particles sizes of approx. 90-100 nm. Antibacterial activity against two pathogens was assessed by minimal inhibitory concentration assays and survival curves. Both pathogens exhibited similar resistance profiles with minimal inhibitory concentrations ranging between 5×10(5) and 10(7) particles/ml. Interestingly, zinc nanoparticles showed a slightly higher efficacy, but sublethal concentrations caused adverse effects and resulted in increased biofilm formation of V. cholerae. Using the expression levels of the outer membrane porin OmpT as an indicator for cAMP levels, our results suggest that zinc nanoparticles inhibit adenylyl cyclase activity. This consequently deceases the levels of this second messenger, which is a known inhibitor of biofilm formation. Finally, we demonstrated that a single oral administration of silver nanoparticles to infant mice colonized with V. cholerae or ETEC significantly reduces the colonization rates of the pathogens by 75- or 100-fold, respectively.

Exploitation of Mycobacterium tuberculosis reporter strains to probe the impact of vaccination at sites of infection

Mycobacterium tuberculosis (Mtb) remains a major public health problem, with an effective vaccine continuing to prove elusive. Progress in vaccination strategies has been hampered by a lack of appreciation of the bacterium's response to dynamic changes in the host immune environment. Here, we utilize reporter Mtb strains that respond to specific host immune stresses such as hypoxia and nitric oxide (hspX'::GFP), and phagosomal maturation (rv2390c'::GFP), to investigate vaccine-induced alterations in the environmental niche during experimental murine infections. While vaccination undoubtedly decreased bacterial burden, we found that it also appeared to accelerate Mtb's adoption of a phenotype better equipped to survive in its host. We subsequently utilized a novel replication reporter strain of Mtb to demonstrate that, in addition to these alterations in host stress response, there is a decreased percentage of actively replicating Mtb in vaccinated hosts. This observation was supported by the differential sensitivity of recovered bacteria to the front-line drug isoniazid. Our study documents the natural history of the impact that vaccination has on Mtb's physiology and replication and highlights the value of reporter Mtb strains for probing heterogeneous Mtb populations in the context of a complex, whole animal model.

Mycobacterium tuberculosis DosR is required for activity of the PmbtB and PmbtI promoters under hypoxia

Mycobacterium tuberculosis has the ability to survive for extended periods of time under conditions of low oxygen, low pH, low iron and low nutrients. The mycobactins (M. tuberculosis siderophores) play a key role in scavenging iron from the environment and are induced in response to low iron in an IdeR-regulated manner. We demonstrate that the promoters of two mycobactin gene (mbt) operons are also expressed during adaptation to low oxygen, and that this expression is dependent on the DosR regulator. Up-regulation of mbt operons induced by low iron was not DosR-dependent. DosR is a member of a two component regulatory system which responds to oxygen availability. Deletion of the DosR regulator led to increased expression of bacterioferritin and increased capacity to grow under iron depletion. These data provide a link between the mycobacterial response to two conditions likely to be encountered in vivo, low iron and low oxygen.

Characterization of a dual-active enzyme, DcpA, involved in cyclic diguanosine monophosphate turnover in Mycobacterium smegmatis

We have reported previously that the long-term survival of Mycobacterium smegmatis is facilitated by a dual-active enzyme MSDGC-1 (renamed DcpA), which controls the cellular turnover of cyclic diguanosine monophosphate (c-di-GMP). Most mycobacterial species possess at least a single copy of a DcpA orthologue that is highly conserved in terms of sequence similarity and domain architecture. Here, we show that DcpA exists in monomeric and dimeric forms. The dimerization of DcpA is due to non-covalent interactions between two protomers that are arranged in a parallel orientation. The dimer shows both synthesis and hydrolysis activities, whereas the monomer shows only hydrolysis activity. In addition, we have shown that DcpA is associated with the cytoplasmic membrane and exhibits heterogeneous cellular localization with a predominance at the cell poles. Finally, we have also shown that DcpA is involved in the change in cell length and colony morphology of M. smegmatis. Taken together, our study provides additional evidence about the role of the bifunctional protein involved in c-di-GMP signalling in M. smegmatis.

Isolation and purification of Mycobacterium tuberculosis from H37Rv infected guinea pig lungs

Evidence suggests that Mycobacterium tuberculosis grown in vivo may have a different phenotypic structure from its in vitro counterpart. In order to study the differences between in vivo and in vitro grown bacilli, it is important to establish a reliable method for isolating and purifying M. tuberculosis from infected tissue. In this study, we developed an optimal method to isolate bacilli from the lungs of infected guinea pigs, which was also shown to be applicable to the interferon-γ gene knockout mouse model. Briefly, 1) the infected lungs were thoroughly homogenized; 2) a four step enzymatic digestion was utilized to reduce the bulk of the host tissue using collagenase, DNase I and pronase E; 3) residual contamination by the host tissue debris was successfully reduced using percoll density gradient centrifugation. These steps resulted in a protocol such that relatively clean, viable bacilli can be isolated from the digested host tissue homogenate in about 50% yield. These bacilli can further be used for analytical studies of the more stable cellular components such as lipid, peptidoglycan and mycolic acid.

Identification of the translational start site of codon-optimized mCherry in Mycobacterium tuberculosis

BACKGROUND

Fluorescent proteins are used widely as reporter genes in many organisms. We previously codon-optimized mCherry for Mycobacterium tuberculosis and generated expression constructs with high level expression in mycobacteria with multiple uses in vitro and in vivo. However, little is known about the expression of fluorescent proteins in mycobacteria and the translational start codon for mCherry has not been experimentally determined.

RESULTS

We determined the translational start site for functional (fluorescent) mCherry in mycobacteria. Several potential translational start codons were identified; introduction of downstream stop codons by mutagenesis was used to determine which start codon was utilized in the bacterial cells. Fluorescent protein was expressed from a construct which would allow translation of a protein of 226 amino acids or a protein of 235 amino acids. No fluorescence was seen when a construct which could give rise to a protein of 219 amino acids was used. Similar results were obtained in mycobacteria and in Escherichia coli. Western blotting confirmed that mCherry was expressed from the constructs encoding 235 or 226 amino acids, but not from the plasmid encoding 219 amino acids. N-terminal sequencing and mass determination confirmed that the mature protein was 226 amino acids and commenced with the amino acid sequence AIIKE.

CONCLUSION

We conclude that mCherry is expressed in M. tuberculosis as a smaller protein than expected lacking the GFP-derived N-terminal sequence designed to allow efficient fusions.

Coupling reporter expression to respiration detects active as well as dormant mycobacteria in vitro and in mouse tissues

BACKGROUND

Mycobacterium tuberculosis is known to slow down its transcriptional activity during dormancy. Hence, while using reporter strains, it is important to couple the reporter gene to a promoter that is strong and sensitive both in active and dormant M. tuberculosis. Since respiration is an indispensable process even in dormant bacteria, validation of the promoters of respiratory chain genes - type II NADH dehydrogenase (Pndh) and adenosine triphosphate (ATP) synthase operon (Patps) - of MTB was undertaken for this purpose.

METHODS

Putative promoter containing sequences were cloned upstream of a red fluorescent protein (RFP) gene. Mycobacterium smegmatis or M. tuberculosis carrying episomal constructs were validated for growth, fitness and fluorescence in different models in vitro and in vivo.

RESULTS

Either promoter can drive stable and strong expression of RFP in actively growing and dormant M. smegmatis in vitro without significantly affecting growth or viability. Fluorescence due to Pndh and Patps was significantly higher than Phsp60. The fitness of M. tuberculosis H37Rv counterparts was unaffected inside J774 macrophages. In immunocompetent mice, despite an initial attenuation in the lungs, both strains reached loads similar to wild type during chronic infection. In the spleen, the fluorescent strain counts were similar to wild type counts throughout. RFP fluorescence in tissue homogenates was more homogenous among mice due to Pndh compared with Patps.

CONCLUSIONS

Coupling an appropriate reporter to the promoter of ndh-2 gene of M. tuberculosis can make the reporter expression respiration sensitive and thereby reliably detect both active and dormant populations of the reporter strain.

WASH-driven actin polymerization is required for efficient mycobacterial phagosome maturation arrest

Pathogenic mycobacteria survive in phagocytic host cells primarily as a result of their ability to prevent fusion of their vacuole with lysosomes, thereby avoiding a bactericidal environment. The molecular mechanisms to establish and maintain this replication compartment are not well understood. By combining molecular and microscopical approaches we show here that after phagocytosis the actin nucleation-promoting factor WASH associates and generates F-actin on the mycobacterial vacuole. Disruption of WASH or depolymerization of F-actin leads to the accumulation of the proton-pumping V-ATPase around the mycobacterial vacuole, its acidification and reduces the viability of intracellular mycobacteria. This effect is observed for M. marinum in the model phagocyte Dictyostelium but also for M. marinum and M. tuberculosis in mammalian phagocytes. This demonstrates an evolutionarily conserved mechanism by which pathogenic mycobacteria subvert the actin-polymerization activity of WASH to prevent phagosome acidification and maturation, as a prerequisite to generate and maintain a replicative niche.

Direct delivery of functional proteins and enzymes to the cytosol using nanoparticle-stabilized nanocapsules

Intracellular protein delivery is an important tool for both therapeutic and fundamental applications. Effective protein delivery faces two major challenges: efficient cellular uptake and avoiding endosomal sequestration. We report here a general strategy for direct delivery of functional proteins to the cytosol using nanoparticle-stabilized capsules (NPSCs). These NPSCs are formed and stabilized through supramolecular interactions between the nanoparticle, the protein cargo, and the fatty acid capsule interior. The NPSCs are ~130 nm in diameter and feature low toxicity and excellent stability in serum. The effectiveness of these NPSCs as therapeutic protein carriers was demonstrated through the delivery of fully functional caspase-3 to HeLa cells with concomitant apoptosis. Analogous delivery of green fluorescent protein (GFP) confirmed cytosolic delivery as well as intracellular targeting of the delivered protein, demonstrating the utility of the system for both therapeutic and imaging applications.

Rapid in vivo assessment of drug efficacy against Mycobacterium tuberculosis using an improved firefly luciferase

Objectives

In vivo experimentation is costly and time-consuming, and presents a major bottleneck in anti-tuberculosis drug development. Conventional methods rely on the enumeration of bacterial colonies, and it can take up to 4 weeks for Mycobacterium tuberculosis to grow on agar plates. Light produced by recombinant bacteria expressing luciferase enzymes can be used as a marker of bacterial load, and disease progression can be easily followed non-invasively in live animals by using the appropriate imaging equipment. The objective of this work was to develop a bioluminescence-based mouse model of tuberculosis to assess antibiotic efficacy against M. tuberculosis in vivo.

Methods

We used an M. tuberculosis strain carrying a red-shifted derivative of the firefly luciferase gene (FFlucRT) to infect mice, and monitored disease progression in living animals by bioluminescence imaging before and after treatment with the frontline anti-tuberculosis drug isoniazid. The resulting images were analysed and the bioluminescence was correlated with bacterial counts.

Results

Using bioluminescence imaging we detected as few as 1.7 × 10³ and 7.5 × 10⁴ reporter bacteria ex vivo and in vivo, respectively, in the lungs of mice. A good correlation was found between bioluminescence and bacterial load in both cases. Furthermore, a marked reduction in luminescence was observed in living mice given isoniazid treatment.

Conclusions

We have shown that an improved bioluminescent strain of M. tuberculosis can be visualized by non-invasive imaging in live mice during an acute, progressive infection and that this technique can be used to rapidly visualize and quantify the effect of antibiotic treatment. We believe that the model presented here will be of great benefit in early drug discovery as an easy and rapid way to identify active compounds in vivo.

Isolation and characterization of antimicrobial compounds in plant extracts against multidrug-resistant Acinetobacter baumannii

The number of fully active antibiotic options that treat nosocomial infections due to multidrug-resistant Acinetobacter baumannii (A. baumannii) is extremely limited. Magnolia officinalis, Mahonia bealei, Rabdosia rubescens, Rosa rugosa, Rubus chingii, Scutellaria baicalensis, and Terminalia chebula plant extracts were previously shown to have growth inhibitory activity against a multidrug-resistant clinical strain of A. baumannii. In this study, the compounds responsible for their antimicrobial activity were identified by fractionating each plant extract using high performance liquid chromatography, and determining the antimicrobial activity of each fraction against A. baumannii. The chemical structures of the fractions inhibiting >40% of the bacterial growth were elucidated by liquid chromatography/mass spectrometry analysis and nuclear magnetic resonance spectroscopy. The six most active compounds were identified as: ellagic acid in Rosa rugosa; norwogonin in Scutellaria baicalensis; and chebulagic acid, chebulinic acid, corilagin, and terchebulin in Terminalia chebula. The most potent compound was identified as norwogonin with a minimum inhibitory concentration of 128 µg/mL, and minimum bactericidal concentration of 256 µg/mL against clinically relevant strains of A. baumannii. Combination studies of norwogonin with ten anti-Gram negative bacterial agents demonstrated that norwogonin did not enhance the antimicrobial activity of the synthetic antibiotics chosen for this study. In conclusion, of all identified antimicrobial compounds, norwogonin was the most potent against multidrug-resistant A. baumannii strains. Further studies are warranted to ascertain the prophylactic and therapeutic potential of norwogonin for infections due to multidrug-resistant A. baumannii.

A dual read-out assay to evaluate the potency of compounds active against Mycobacterium tuberculosis

Tuberculosis is a serious global health problem caused by the bacterium Mycobacterium tuberculosis. There is an urgent need for discovery and development of new treatments, but this can only be accomplished through rapid and reproducible M. tuberculosis assays designed to identify potent inhibitors. We developed an automated 96-well assay utilizing a recombinant strain of M. tuberculosis expressing a far-red fluorescent reporter to determine the activity of novel compounds; this allowed us to measure growth by monitoring both optical density and fluorescence. We determined that optical density and fluorescence were correlated with cell number during logarithmic phase growth. Fluorescence was stably maintained without antibiotic selection over 5 days, during which time cells remained actively growing. We optimized parameters for the assay, with the final format being 5 days' growth in 96-well plates in the presence of 2% w/v DMSO. We confirmed reproducibility using rifampicin and other antibiotics. The dual detection method allows for a reproducible calculation of the minimum inhibitory concentration (MIC), at the same time detecting artefacts such as fluorescence quenching or compound precipitation. We used our assay to confirm anti-tubercular activity and establish the structure activity relationship (SAR) around the imidazo[1,2-a]pyridine-3-carboxamides, a promising series of M. tuberculosis inhibitors.

Mycobacterium tuberculosis responds to chloride and pH as synergistic cues to the immune status of its host cell

The ability of Mycobacterium tuberculosis (Mtb) to thrive in its phagosomal niche is critical for its establishment of a chronic infection. This requires that Mtb senses and responds to intraphagosomal signals such as pH. We hypothesized that Mtb would respond to additional intraphagosomal factors that correlate with maturation. Here, we demonstrate that [Cl⁻] and pH correlate inversely with phagosome maturation, and identify Cl⁻ as a novel environmental cue for Mtb. Mtb responds to Cl⁻ and pH synergistically, in part through the activity of the two-component regulator phoPR. Following identification of promoters responsive to Cl⁻ and pH, we generated a reporter Mtb strain that detected immune-mediated changes in the phagosomal environment during infection in a mouse model. Our study establishes Cl⁻ and pH as linked environmental cues for Mtb, and illustrates the utility of reporter bacterial strains for the study of Mtb-host interactions in vivo.

Cooccurrence of free-living amoebae and nontuberculous Mycobacteria in hospital water networks, and preferential growth of Mycobacterium avium in Acanthamoeba lenticulata

The incidence of lung and other diseases due to nontuberculous mycobacteria (NTM) is increasing. NTM sources include potable water, especially in households where NTM populate pipes, taps, and showerheads. NTM share habitats with free-living amoebae (FLA) and can grow in FLA as parasites or as endosymbionts. FLA containing NTM may form cysts that protect mycobacteria from disinfectants and antibiotics. We first assessed the presence of FLA and NTM in water and biofilm samples collected from a hospital, confirming the high prevalence of NTM and FLA in potable water systems, particularly in biofilms. Acanthamoeba spp. (genotype T4) were mainly recovered (8/17), followed by Hartmannella vermiformis (7/17) as well as one isolate closely related to the genus Flamella and one isolate only distantly related to previously described species. Concerning mycobacteria, Mycobacterium gordonae was the most frequently found isolate (9/17), followed by Mycobacterium peregrinum (4/17), Mycobacterium chelonae (2/17), Mycobacterium mucogenicum (1/17), and Mycobacterium avium (1/17). The propensity of Mycobacterium avium hospital isolate H87 and M. avium collection strain 104 to survive and replicate within various FLA was also evaluated, demonstrating survival of both strains in all amoebal species tested but high replication rates only in Acanthamoeba lenticulata. As A. lenticulata was frequently recovered from environmental samples, including drinking water samples, these results could have important consequences for the ecology of M. avium in drinking water networks and the epidemiology of disease due to this species.

Infection of macrophages with Mycobacterium tuberculosis induces global modifications to phagosomal function

The phagosome is a central mediator of both the homeostatic and microbicidal functions of a macrophage. Following phagocytosis, Mycobacterium tuberculosis (Mtb) is able to establish infection through arresting phagosome maturation and avoiding the consequences of delivery to the lysosome. The infection of a macrophage by Mtb leads to marked changes in the behaviour of both the macrophage and the surrounding tissue as the bacterium modulates its environment to promote its survival. In this study, we use functional physiological assays to probe the biology of the phagosomal network in Mtb-infected macrophages. The resulting data demonstrate that Mtb modifies phagosomal function in a TLR2/TLR4-dependent manner, and that most of these modifications are consistent with an increase in the activation status of the cell. Specifically, superoxide burst is enhanced and lipolytic activity is decreased upon infection. There are some species- or cell type-specific differences between human and murine macrophages in the rates of acidification and the degree of proteolysis. However, the most significant modification is the marked reduction in intra-phagosomal lipolysis because this correlates with the marked increase in the retention of host lipids in the infected macrophage, which provides a potential source of nutrients that can be accessed by Mtb.

The granuloma in tuberculosis: dynamics of a host-pathogen collusion

A granuloma is defined as an inflammatory mononuclear cell infiltrate that, while capable of limiting growth of Mycobacterium tuberculosis, also provides a survival niche from which the bacteria may disseminate. The tuberculosis lesion is highly dynamic and shaped by both, immune response elements and the pathogen. In the granuloma, M. tuberculosis switches to a non-replicating but energy-generating life style whose detailed molecular characterization can identify novel targets for chemotherapy. To secure transmission to a new host, M. tuberculosis has evolved to drive T cell immunity to the point that necrotizing granulomas leak into bronchial cavities to facilitate expectoration of bacilli. From an evolutionary perspective it is therefore questionable whether vaccination and immunity enhancing strategies that merely mimic the natural immune response directed against M. tuberculosis infection can overcome pulmonary tuberculosis in the adult population. Juxtaposition of molecular pathology and immunology with microbial physiology and the use of novel imaging approaches afford an integrative view of the granuloma’s contribution to the life cycle of M. tuberculosis. This review revisits the different input of innate and adaptive immunity in granuloma biogenesis, with a focus on the co-evolutionary forces that redirect immune responses also to the benefit of the pathogen, i.e., its survival, propagation, and transmission.

Antimycobacterial activity evaluation, time-kill kinetic and 3D-QSAR study of C-(3-aminomethyl-cyclohexyl)-methylamine derivatives

A series of C-(3-aminomethyl-cyclohexyl)-methylamine derivatives were synthesized and evaluated for their antitubercular activity. Some of the compounds exhibited potent activity against Mycobacterium tuberculosis H37Rv. One of the compound having t-butyl at para position of the benzene ring showed excellent activity even better than the standard drug ethambutol with MIC value 1.1 ± 0.2 μM. The time-kill kinetics study of two most active compounds showed rapid killing of the M. tuberculosis within 4 days. Additionally atom-based quantitative structure-activity relationship (QSAR) model was developed that gave a statistically satisfying result (R(2))=0.92, Q(2)=0.75, Pearson-R=0.96 and effectively predicts the anti-tuberculosis activity of training and test set compounds.

Setting up and monitoring an infection of Dictyostelium discoideum with mycobacteria

Mycobacterium marinum is the causative agent of fish and amphibian tuberculosis in the wild. It is a genetically close cousin of Mycobacterium tuberculosis, and thereby the infection process remarkably shares many of the hallmarks of M. tuberculosis infection in human, at both the cellular and organism levels. Therefore, M. marinum is used as a model for the study of mycobacterial infection in various host organisms. Recently, the Dictyostelium-M. marinum system has been shown to be a valuable model that recapitulates the main features of the intracellular fate of M. marinum including phagosome maturation arrest, as well as its particular cell-to-cell dissemination mode. We present here a "starter kit" of detailed methods that allows to establish an infection of Dictyostelium with M. marinum and to monitor quantitatively the intracellular bacterial growth.

Patterning of Protein/Quantum Dot Hybrid Bionanostructures

Here we demonstrate patterning of protein/quantum dot hybrid bionanostructures via electrostatic assembly of engineered negatively charged fluorescent protein with positively charged CdSe/ZnS QD patterns formed through e-beam lithography and post-patterning modification with cationic ligands.

A new in vivo model to test anti-tuberculosis drugs using fluorescence imaging

OBJECTIVES

The current method for testing new drugs against tuberculosis in vivo is the enumeration of bacteria in organs by cfu assay. Owing to the slow growth rate of Mycobacterium tuberculosis (Mtb), these assays can take months to complete. Our aim was to develop a more efficient, fluorescence-based imaging assay to test new antibiotics in a mouse model using Mtb reporter strains.

METHODS

A commercial IVIS Kinetic® system and a custom-built laser scanning system with fluorescence molecular tomography (FMT) capability were used to detect fluorescent Mtb in living mice and lungs ex vivo. The resulting images were analysed and the fluorescence was correlated with data from cfu assays.

RESULTS

We have shown that fluorescent Mtb can be visualized in the lungs of living mice at a detection limit of ∼8 × 10⁷ cfu/lung, whilst in lungs ex vivo a detection limit of ∼2 × 10⁵ cfu/lung was found. These numbers were comparable between the two imaging systems. Ex vivo lung fluorescence correlated to numbers of bacteria in tissue, and the effect of treatment of mice with the antibiotic moxifloxacin could be visualized and quantified after only 9 days through fluorescence measurements, and was confirmed by cfu assays.

CONCLUSIONS

We have developed a new and efficient method for anti-tuberculosis drug testing in vivo, based on fluorescent Mtb reporter strains. Using this method instead of, or together with, cfu assays will reduce the time required to assess the preclinical efficacy of new drugs in animal models and enhance the progress of these candidates into clinical trials against human tuberculosis.

The promoter of Rv0560c is induced by salicylate and structurally-related compounds in Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a major global health threat. During infection, bacteria are believed to encounter adverse conditions such as iron depletion. Mycobacteria synthesize iron-sequestering mycobactins, which are essential for survival in the host, via the intermediate salicylate. Salicylate is a ubiquitous compound which is known to induce a mild antibiotic resistance phenotype. In M. tuberculosis salicylate highly induces the expression of Rv0560c, a putative methyltransferase. We identified and characterized the promoter and regulatory elements of Rv0560c. P_Rv0560c activity was highly inducible by salicylate in a dose-dependent manner. The induction kinetics of P_Rv0560c were slow, taking several days to reach maximal activity, which was sustained over several weeks. Promoter activity could also be induced by compounds structurally related to salicylate, such as aspirin or para-aminosalicylic acid, but not by benzoate, indicating that induction is specific to a structural motif. The −10 and −35 promoter elements were identified and residues involved in regulation of promoter activity were identified in close proximity to an inverted repeat spanning the −35 promoter element. We conclude that Rv0560c expression is controlled by a yet unknown repressor via a highly-inducible promoter.

Expression of common fluorescent reporters may modulate virulence for Mycobacterium marinum: dramatic attenuation results from Gfp over-expression

Mycobacterium marinum is an established surrogate pathogen for Mycobacterium tuberculosis because of its strong conservation of thousands of orthologous genes, lower risk to researchers and similar pathology in fish. This pathogen causes TB-like chronic disease in a wide variety of fish species. As in human TB, the microbe grows within the host macrophages, can mount life-long chronic infections and produces granulomatous lesions in target organs. One of the fish species known to manifest chronic "fish TB" is the small laboratory fish, Japanese ricefish (medaka; Oryzias latipes). Our laboratory is currently characterizing the disease progression in medaka using fluorescent reporter systems that are introduced into engineered strains of M. marinum. While conducting these studies we observed differences in growth, plasmid stability, and virulence depending on which fluorescent reporter construct was present. Here, we describe large negative effects on virulence and organ colonization that occurred with a commonly used plasmid pG13, that expresses green fluorescent protein (Gfp). The studies presented here, indicate that Gfp over-expression was the basis for the reduced virulence in this reporter construct. We also show that these negative effects could be reversed by significantly reducing Gfp expression levels or by using low-expression constructs of Rfp.

Whole-body imaging of infection using fluorescence

Optical imaging is emerging as a powerful tool to study physiological, neurological, oncological, cell biological, molecular, developmental, immunological, and infectious processes. This unit describes the use of fluorescent reporters for biological organisms, components, or events. We describe the application of fluorescence imaging to examination of infectious processes, in particular subcutaneous and pulmonary bacterial infections, but the same approaches are applicable to nearly any infectious route. The strategies described use mycobacterial infections as an example, but nearly identical systems can be used for Pseudomonas, Legionella, Salmonella, Escherichia, Borrelia, and Staphylococus, suggesting that the approaches are generally applicable to nearly any infectious agent. Two strategies for fluorescence imaging are described: the first method uses reporter enzyme fluorescence (REF), and the second uses fluorescent proteins for fluorescence imaging. Methods are described in detail to facilitate successful application of these emerging technologies to nearly any experimental system.

aprABC: a Mycobacterium tuberculosis complex-specific locus that modulates pH-driven adaptation to the macrophage phagosome

Following phagocytosis by macrophages, Mycobacterium tuberculosis (Mtb) senses the intracellular environment and remodels its gene expression for growth in the phagosome. We have identified an acid and phagosome regulated (aprABC) locus that is unique to the Mtb complex and whose gene expression is induced during growth in acidic environments in vitro and in macrophages. Using the aprA promoter, we generated a strain that exhibits high levels of inducible fluorescence in response to growth in acidic medium in vitro and in macrophages. aprABC expression is dependent on the two-component regulator phoPR, linking phoPR signalling to pH sensing. Deletion of the aprABC locus causes defects in gene expression that impact aggregation, intracellular growth, and the relative levels of storage and cell wall lipids. We propose a model where phoPR senses the acidic pH of the phagosome and induces aprABC expression to fine-tune processes unique for intracellular adaptation of Mtb complex bacteria.

Stage-specific fluorescence intensity of GFP and mCherry during sporulation In Bacillus Subtilis

Background

Fluorescent proteins are powerful molecular biology tools that have been used to study the subcellular dynamics of proteins within live cells for well over a decade. Two fluorescent proteins commonly used to enable dual protein labelling are GFP (green) and mCherry (red). Sporulation in the Gram positive bacterium Bacillus subtilis has been studied for many years as a paradigm for understanding the molecular basis for differential gene expression. As sporulation initiates, cells undergo an asymmetric division leading to differential gene expression in the small prespore and large mother cell compartments. Use of two fluorescent protein reporters permits time resolved examination of differential gene expression either in the same compartments or between compartments. Due to the spectral properties of GFP and mCherry, they are considered an ideal combination for co-localisation and co-expression experiments. They can also be used in combination with fluorescent DNA stains such as DAPI to correlate protein localisation patterns with the developmental stage of sporulation which can be linked to well characterised changes in DNA staining patterns.

Findings

While observing the recruitment of the transcription machinery into the forespore of sporulating Bacillus subtilis, we noticed the occurrence of stage-specific fluorescence intensity differences between GFP and mCherry. During vegetative growth and the initial stages of sporulation, fluorescence from both GFP and mCherry fusions behaved similarly. During stage II-III of sporulation we found that mCherry fluorescence was considerably diminished, whilst GFP signals remained clearly visible. This fluorescence pattern reversed during the final stage of sporulation with strong mCherry and low GFP fluorescence. These trends were observed in reciprocal tagging experiments indicating a direct effect of sporulation on fluorescent protein fluorophores.

Conclusions

Great care should be taken when interpreting the results of protein localisation and quantitative gene expression patterns using fluorescent proteins in experiments involving intracellular physiological change. We believe changes in the subcellular environment of the sporulating cell leads to conditions that differently alter the spectral properties of GFP and mCherry making an accurate interpretation of expression profiles technically challenging.

Noninvasive biophotonic imaging for studies of infectious disease

According to World Health Organization estimates, infectious organisms are responsible for approximately one in four deaths worldwide. Animal models play an essential role in the development of vaccines and therapeutic agents but large numbers of animals are required to obtain quantitative microbiological data by tissue sampling. Biophotonic imaging (BPI) is a highly sensitive, nontoxic technique based on the detection of visible light, produced by luciferase-catalysed reactions (bioluminescence) or by excitation of fluorescent molecules, using sensitive photon detectors. The development of bioluminescent/fluorescent microorganisms therefore allows the real-time noninvasive detection of microorganisms within intact living animals. Multiple imaging of the same animal throughout an experiment allows disease progression to be followed with extreme accuracy, reducing the number of animals required to yield statistically meaningful data. In the study of infectious disease, the use of BPI is becoming widespread due to the novel insights it can provide into established models, as well as the impact of the technique on two of the guiding principles of using animals in research, namely reduction and refinement. Here, we review the technology of BPI, from the instrumentation through to the generation of a photonic signal, and illustrate how the technique is shedding light on infection dynamics in vivo.

Optimisation of bioluminescent reporters for use with mycobacteria

Background

Mycobacterium tuberculosis, the causative agent of tuberculosis, still represents a major public health threat in many countries. Bioluminescence, the production of light by luciferase-catalyzed reactions, is a versatile reporter technology with multiple applications both in vitro and in vivo. In vivo bioluminescence imaging (BLI) represents one of its most outstanding uses by allowing the non-invasive localization of luciferase-expressing cells within a live animal. Despite the extensive use of luminescent reporters in mycobacteria, the resultant luminescent strains have not been fully applied to BLI.

Methodology/Principal Findings

One of the main obstacles to the use of bioluminescence for in vivo imaging is the achievement of reporter protein expression levels high enough to obtain a signal that can be detected externally. Therefore, as a first step in the application of this technology to the study of mycobacterial infection in vivo, we have optimised the use of firefly, Gaussia and bacterial luciferases in mycobacteria using a combination of vectors, promoters, and codon-optimised genes. We report for the first time the functional expression of the whole bacterial lux operon in Mycobacterium tuberculosis and M. smegmatis thus allowing the development of auto-luminescent mycobacteria. We demonstrate that the Gaussia luciferase is secreted from bacterial cells and that this secretion does not require a signal sequence. Finally we prove that the signal produced by recombinant mycobacteria expressing either the firefly or bacterial luciferases can be non-invasively detected in the lungs of infected mice by bioluminescence imaging.

Conclusions/Significance

While much work remains to be done, the finding that both firefly and bacterial luciferases can be detected non-invasively in live mice is an important first step to using these reporters to study the pathogenesis of M. tuberculosis and other mycobacterial species in vivo. Furthermore, the development of auto-luminescent mycobacteria has enormous ramifications for high throughput mycobacterial drug screening assays which are currently carried out either in a destructive manner using LuxAB or the firefly luciferase.