In vivo inhibition of tryptophan catabolism reorganizes the tuberculoma and augments immune-mediated control of Mycobacterium tuberculosis.

Mycobacterium tuberculosis continues to cause devastating levels of mortality due to tuberculosis (TB). The failure to control TB stems from an incomplete understanding of the highly specialized strategies that M. tuberculosis utilizes to modulate host immunity and thereby persist in host lungs. Here, we show that M. tuberculosis induced the expression of indoleamine 2,3-dioxygenase (IDO), an enzyme involved in tryptophan catabolism, in macrophages and in the lungs of animals (mice and macaque) with active disease. In a macaque model of inhalation TB, suppression of IDO activity reduced bacterial burden, pathology, and clinical signs of TB disease, leading to increased host survival. This increased protection was accompanied by increased lung T cell proliferation, induction of inducible bronchus-associated lymphoid tissue and correlates of bacterial killing, reduced checkpoint signaling, and the relocation of effector T cells to the center of the granulomata. The enhanced killing of M. tuberculosis in macrophages in vivo by CD4+ T cells was also replicated in vitro, in cocultures of macaque macrophages and CD4+ T cells. Collectively, these results suggest that there exists a potential for using IDO inhibition as an effective and clinically relevant host-directed therapy for TB.

Reinstating Mycobacterium massiliense and Mycobacterium bolletii as species of the Mycobacterium abscessus complex.

TheMycobacterium abscessus complex is a group of rapidly growing, multiresistant mycobacteria previously divided into three species. Proposal for the union of Mycobacterium bolletii and Mycobacterium massiliense into one subspecies, so-called M. abscessus subsp. massiliense, created much confusion about the routine identification and reporting of M. abscessus clinical isolates for clinicians. Results derived from multigene sequencing unambiguously supported the reinstatement of M. massiliense and M. bolletii as species, culminating in the presence of erm(41)-encoded macrolide resistance in M. bolletii. Present genome-based analysis unambiguously supports the reinstatement of M. massiliense and M. bolletii as species after the average nucleotide identity values of 96.7 % for M. abscessus versus M. bolletii, and 96.4 % for M. abscessus versus M. massiliense, and the 96.6 % identity between M. bolletii and M. massiliense was put into the perspective of a larger, 28-species analysis. Accordingly, DNA-DNA hybridization values predicted by the complete rpoB gene sequencing analysis were between 68.7 and 72.3 % in this complex. These genomic data as well as the phenotypic characteristics prompted us to propose to reinstate the previously known M. massiliense and M. bolletii into two distinct species among the M. abscessus complex.

Mycobacterium tuberculosis impairs dendritic cell functions through the serine hydrolase Hip1.

Mycobacterium tuberculosis is a highly successful human pathogen that primarily resides in host phagocytes, such as macrophages and dendritic cells (DCs), and interferes with their functions. Although multiple strategies used by M. tuberculosis to modulate macrophage responses have been discovered, interactions between M. tuberculosis and DCs are less well understood. DCs are the primary APCs of the immune system and play a central role in linking innate and adaptive immune responses to microbial pathogens. In this study, we show that M. tuberculosis impairs DC cytokine secretion, maturation, and Ag presentation through the cell envelope-associated serine hydrolase, Hip1. Compared to wild-type, a hip1 mutant strain of M. tuberculosis induced enhanced levels of the key Th1-inducing cytokine IL-12, as well as other proinflammatory cytokines (IL-23, IL-6, TNF-α, IL-1ß, and IL-18) in DCs via MyD88- and TLR2/9-dependent pathways, indicating that Hip1 restricts optimal DC inflammatory responses. Infection with the hip1 mutant also induced higher levels of MHC class II and costimulatory molecules CD40 and CD86, indicating that M. tuberculosis impairs DC maturation through Hip1. Further, we show that M. tuberculosis promotes suboptimal Ag presentation, as DCs infected with the hip1 mutant showed increased capacity to present Ag to OT-II- and early secreted antigenic target 6-specific transgenic CD4 T cells and enhanced Th1 and Th17 polarization. Overall, these data show that M. tuberculosis impairs DC functions and modulates the nature of Ag-specific T cell responses, with important implications for vaccination strategies.

Impaired degranulation and proliferative capacity of Mycobacterium tuberculosis-specific CD8+ T cells in HIV-infected individuals with latent tuberculosis.

Human immunodeficiency virus (HIV)-infected individuals with latent Mycobacterium tuberculosis infection have substantially higher rates of progression to active tuberculosis than HIV-uninfected individuals with latent tuberculosis. To explore HIV-induced deficits in M. tuberculosis-specific CD8+ T-cell functions, we compared interferon γ production, degranulation, and proliferation of CD8+ T cells in response to M. tuberculosis peptides (ESAT-6/CFP-10) between HIV-infected (median CD4+ T-cell count, 522 cells/µL; interquartile range, 318-585 cells/µL) and HIV-uninfected individuals with latent tuberculosis from South Africa. We found that M. tuberculosis-specific degranulation and proliferative capacities were impaired in the HIV-infected group. Thus, our results suggest that HIV coinfection compromises CD8+ T-cell functions in latent tuberculosis.

The rpoB gene as a tool for clinical microbiologists.

The rpoB gene, encoding the beta-subunit of RNA polymerase, has emerged as a core gene candidate for phylogenetic analyses and identification of bacteria, especially when studying closely related isolates. Together with the 16S rRNA gene, rpoB has helped to delineate new bacterial species and refine bacterial community analysis, as well as enabling the monitoring of rifampicin resistance-conferring mutations. Sequencing of rpoB enables efficient estimation of bacterial G+C% content, DNA-DNA hybridization value and average nucleotide identity (percentage of the total genomic sequence shared between two strains) when taxonomic relationships have been firmly established. New identification tools targeting a rpoB gene fragment located between positions 2300 and 3300 have been developed recently. Therefore, inclusion of the rpoB gene sequence would be useful when describing new bacterial species.

Revival and emended description of 'Mycobacterium paraffinicum' Davis, Chase and Raymond 1956 as Mycobacterium paraffinicum sp. nov., nom. rev.

The omission of the name 'Mycobacterium paraffinicum' from the Approved Lists of Bacterial Names was due to phenotypic confusion surrounding a close relationship with Mycobacterium scrofulaceum. Correspondingly, 'M. paraffinicum' strains grew slowly in > 7 days, stained acid-alcohol-fast and produced yellow-pigmented, smooth, waxy colonies in the dark at an optimal temperature of 35°C. However, 'M. paraffinicum' strains demonstrated no activity for urease, nicotinamidase or pyrazinamidase and lacked growth at 42°C, unlike M. scrofulaceum. The mycolic acid pattern, as determined by HPLC, clustered 'M. paraffinicum' with M. scrofulaceum, Mycobacterium avium and Mycobacterium parascrofulaceum. Strains were fully susceptible to linezolid, rifabutin, clarithromycin and amikacin. Examination of the historical reference strain of 'M. paraffinicum', ATCC 12670, and five additional isolates using comparative studies with 16S rRNA, hsp65 and rpoB gene and concatenated sequences showed that they formed a tight taxonomic group that was distinct from similar non-tuberculous mycobacteria. Multilocus enzyme electrophoresis (MEE) analysis confirmed a close association of the five additional isolates with the reference strain of 'M. paraffinicum' with a genetic distance of 0.12 and showed that all six strains were distinct from other closely related species. These genetic results provided unambiguous evidence of the uniqueness of this slowly growing, scotochromogenic species and supported the revival of the name as Mycobacterium paraffinicum (ex Davis, Chase and Raymond 1956) sp. nov., nom. rev. We propose the previously deposited reference strain ATCC 12670(T) =DSM 44181(T) =NCIMB 10420(T), located in collections worldwide, as the type strain.

Mycobacterium bolletii respiratory infections.

Contrary to other species in the Mycobacterium chelonae-abscessus complex, we reidentified M. bolletii strains isolated from 4 respiratory patients and found these strains to be uniformly resistant to clarithromycin. No mutations previously associated with macrolide resistance in bacteria were detected in either the 23S rDNA or the genes encoding riboproteins L4 and L22.

Multiphasic approach reveals genetic diversity of environmental and patient isolates of Mycobacterium mucogenicum and Mycobacterium phocaicum associated with an outbreak of bacteremias at a Texas hospital.

Between March and May 2006, a Texas hospital identified five Mycobacterium mucogenicum bloodstream infections among hospitalized oncology patients using fluorescence high-performance liquid chromatography analysis of mycolic acids. Isolates from blood cultures were compared to 16 isolates from environmental sites or water associated with this ward. These isolates were further characterized by hsp65, 16S rRNA, and rpoB gene sequencing, hsp65 PCR restriction analysis, and molecular typing methods, including repetitive element PCR, random amplified polymorphic DNA PCR, and pulsed-field gel electrophoresis (PFGE) of large restriction fragments. Three of five patient isolates were confirmed as M. mucogenicum and were in a single cluster as determined by all identification and typing methods. The remaining two patient isolates were identified as different strains of Mycobacterium phocaicum by rpoB sequence analysis. One of these matched an environmental isolate from a swab of a hand shower in the patient's room, while none of the clinical isolates of M. mucogenicum matched environmental strains. Among the other 15 environmental isolates, 11 were identified as M. mucogenicum and 4 as M. phocaicum strains, all of which were unrelated by typing methods. Although the 16S rRNA gene sequences matched for all 14 M. mucogenicum isolates, there were two each of the hsp65 and rpoB sequevars, seven PCR typing patterns, and 12 PFGE patterns. Among the seven M. phocaicum isolates were three 16S rRNA sequevars, two hsp65 sequevars, two rpoB sequevars, six PCR typing patterns, and six PFGE patterns. This outbreak represents the first case of catheter-associated bacteremia caused by M. phocaicum and the first report of clinical isolates from a U.S. hospital. The investigation highlights important differences in the available typing methods for mycobacteria and demonstrates the genetic diversity of these organisms even within narrow confines of time and space.

High Frequencies of Caspase-3 Expressing Mycobacterium tuberculosis-Specific CD4+ T Cells Are Associated With Active Tuberculosis.

Antigen-specific CD4+ T cell responses to Mycobacterium tuberculosis (Mtb) infection are important for host defense against tuberculosis (TB). However, Mtb-specific IFN-γ-producing T cells do not distinguish active tuberculosis (ATB) patients from individuals with asymptomatic latent Mtb infection (LTBI). We reasoned that the immune phenotype of Mtb-specific IFN-γ+CD4+ T cells could provide an indirect gauge of Mtb antigen load within individuals. We sought to identify immune markers in Mtb-specific IFN-γ+CD4+ T cells and hypothesized that expression of caspase-3 Mtb-specific CD4+ T cells would be associated with ATB. Using polychromatic flow cytometry, we evaluated the expression of caspase-3 in Mtb-specific CD4+ T cells from LTBI and ATB as well as from ATB patients undergoing anti-TB treatment. We found significantly higher frequencies of Mtb-specific caspase-3+IFN-γ+CD4+ T cells in ATB compared to LTBI. Caspase-3+IFN-γ+CD4+ T cells were also more activated compared to their caspase-3-negative counterparts. Furthermore, the frequencies of caspase-3+IFN-γ+CD4+ T cells decreased in response to anti-TB treatment. Our studies suggest that the frequencies of caspase-3-expressing antigen-specific CD4+ T cells may reflect mycobacterial burden in vivo and may be useful for distinguishing Mtb infection status along with other host biomarkers.

Neutrophil extracellular trap (NET) levels in human plasma are associated with active TB.

Neutrophils are increasingly associated with tuberculosis (TB) disease. Neutrophil extracellular traps (NETs), which are released by neutrophils as a host antimicrobial defense mechanism, are also associated with tissue damage. However, a link between NET levels and TB disease has not been studied. Here we investigate plasma NETs levels in patients with active pulmonary tuberculosis using an ELISA assay that is suitable for high-throughput processing. We show that plasma NETs levels at baseline correlated with disease severity and decreased with antibiotic therapy. Our study demonstrates the biologic plausibility of measuring NETs in plasma samples from patients with TB.

Isolation of Mycobacterium septicum from the sputum of a patient suffering from hemoptoic pneumonia.

A rapidly growing mycobacterium was isolated in pure culture from the sputum of a 78-year-old woman suffering from hemoptoic pneumonia. The isolate exhibited an antimicrobial susceptibility pattern and a biochemical profile similar to that of Mycobacterium septicum ATCC 700731(T) and shared 100% 16S rRNA gene sequence similarity with this type strain over 1480 bp. Its partial rpoB sequence shared 98.2% similarity with the latter species, suggesting the isolate was representative of a sequevar of M. septicum. Contrary to the type strain, this isolate was resistant to azithromycin, erythromycin, vancomycin and tobramycin. This case illustrates the first isolation from sputum of M. septicum, a member of the Mycobacterium fortuitum group previously isolated once from bacteremia. Strain D13 has been deposited in the Collection de l'Institut Pasteur as CIP 108512.

Prevotella massiliensis sp. nov. isolated from human blood.

We report a bacterial isolate (Marseille isolate) recovered from the blood of a patient hospitalized in an intensive care unit, presenting with severe trauma, fever and mechanical ventilation. Colonies appeared at 37 degrees C on blood agar after 72 h incubation. This isolate was a strictly anaerobic, Gram-negative rod phenotypically related to other Prevotella species described to date: non-motile, catalase-negative, oxidase-positive, non-glucose fermenting, resistant to vancomycin and susceptible to kanamycin. Cells exhibited a trilamellar membrane under electron microscopy. The fatty acid methyl ester profile was marginally related to that of Clostridium botulinum group A (distance: 26.27%) and Bifidobacterium bifidum GC subgroup B (distance: 26.38%). 16S rRNA gene sequence similarity was 90.0% with that of Prevotella oris and 89.1% with that of Prevotella melaninogenica. Partial rpoB gene sequence similarity was 84.5 and 86.4% with P. oris and P. melaninogenica, respectively. According to current standards, phenotypic traits, 16S rRNA and rpoB gene sequence analyses indicated that the Marseille isolate belonged to a previously unrecognized species of the genus Prevotella, and we propose classifying it in the new taxon "Prevotella massiliensis" sp. nov.

Biomarkers on patient T cells diagnose active tuberculosis and monitor treatment response.

BACKGROUND: The identification and treatment of individuals with tuberculosis (TB) is a global public health priority. Accurate diagnosis of pulmonary active TB (ATB) disease remains challenging and relies on extensive medical evaluation and detection of Mycobacterium tuberculosis (Mtb) in the patient's sputum. Further, the response to treatment is monitored by sputum culture conversion, which takes several weeks for results. Here, we sought to identify blood-based host biomarkers associated with ATB and hypothesized that immune activation markers on Mtb-specific CD4+ T cells would be associated with Mtb load in vivo and could thus provide a gauge of Mtb infection. METHODS: Using polychromatic flow cytometry, we evaluated the expression of immune activation markers on Mtb-specific CD4+ T cells from individuals with asymptomatic latent Mtb infection (LTBI) and ATB as well as from ATB patients undergoing anti-TB treatment. RESULTS: Frequencies of Mtb-specific IFN-γ+CD4+ T cells that expressed immune activation markers CD38 and HLA-DR as well as intracellular proliferation marker Ki-67 were substantially higher in subjects with ATB compared with those with LTBI. These markers accurately classified ATB and LTBI status, with cutoff values of 18%, 60%, and 5% for CD38+IFN-γ+, HLA-DR+IFN-γ+, and Ki-67+IFN-γ+, respectively, with 100% specificity and greater than 96% sensitivity. These markers also distinguished individuals with untreated ATB from those who had successfully completed anti-TB treatment and correlated with decreasing mycobacterial loads during treatment. CONCLUSION: We have identified host blood-based biomarkers on Mtb-specific CD4+ T cells that discriminate between ATB and LTBI and provide a set of tools for monitoring treatment response and cure. TRIAL REGISTRATION: Registration is not required for observational studies. FUNDING: This study was funded by Emory University, the NIH, and the Yerkes National Primate Center.

Mucosal vaccination with attenuated Mycobacterium tuberculosis induces strong central memory responses and protects against tuberculosis.

Tuberculosis (TB) is a global pandaemic, partially due to the failure of vaccination approaches. Novel anti-TB vaccines are therefore urgently required. Here we show that aerosol immunization of macaques with the Mtb mutant in SigH (MtbΔsigH) results in significant recruitment of inducible bronchus-associated lymphoid tissue (iBALT) as well as CD4(+) and CD8(+) T cells expressing activation and proliferation markers to the lungs. Further, the findings indicate that pulmonary vaccination with MtbΔsigH elicited strong central memory CD4(+) and CD8(+) T-cell responses in the lung. Vaccination with MtbΔsigH results in significant protection against a lethal TB challenge, as evidenced by an approximately three log reduction in bacterial burdens, significantly diminished clinical manifestations and granulomatous pathology and characterized by the presence of profound iBALT. This highly protective response is virtually absent in unvaccinated and BCG-vaccinated animals after challenge. These results suggest that future TB vaccine candidates can be developed on the basis of MtbΔsigH.

Distinct effector memory CD4+ T cell signatures in latent Mycobacterium tuberculosis infection, BCG vaccination and clinically resolved tuberculosis.

Two billion people worldwide are estimated to be latently infected with Mycobacterium tuberculosis (Mtb) and are at risk for developing active tuberculosis since Mtb can reactivate to cause TB disease in immune-compromised hosts. Individuals with latent Mtb infection (LTBI) and BCG-vaccinated individuals who are uninfected with Mtb, harbor antigen-specific memory CD4(+) T cells. However, the differences between long-lived memory CD4(+) T cells induced by latent Mtb infection (LTBI) versus BCG vaccination are unclear. In this study, we characterized the immune phenotype and functionality of antigen-specific memory CD4(+) T cells in healthy BCG-vaccinated individuals who were either infected (LTBI) or uninfected (BCG) with Mtb. Individuals were classified into LTBI and BCG groups based on IFN-γ ELISPOT using cell wall antigens and ESAT-6/CFP-10 peptides. We show that LTBI individuals harbored high frequencies of late-stage differentiated (CD45RA(-)CD27(-)) antigen-specific effector memory CD4(+) T cells that expressed PD-1. In contrast, BCG individuals had primarily early-stage (CD45RA(-)CD27(+)) cells with low PD-1 expression. CD27(+) and CD27(-) as well as PD-1(+) and PD-1(-) antigen-specific subsets were polyfunctional, suggesting that loss of CD27 expression and up-regulation of PD-1 did not compromise their capacity to produce IFN-γ, TNF-α and IL-2. PD-1 was preferentially expressed on CD27(-) antigen-specific CD4(+) T cells, indicating that PD-1 is associated with the stage of differentiation. Using statistical models, we determined that CD27 and PD-1 predicted LTBI versus BCG status in healthy individuals and distinguished LTBI individuals from those who had clinically resolved Mtb infection after anti-tuberculosis treatment. This study shows that CD4(+) memory responses induced by latent Mtb infection, BCG vaccination and clinically resolved Mtb infection are immunologically distinct. Our data suggest that differentiation into CD27(-)PD-1(+) subsets in LTBI is driven by Mtb antigenic stimulation in vivo and that CD27 and PD-1 have the potential to improve our ability to evaluate true LTBI status.

Core gene set as the basis of multilocus sequence analysis of the subclass Actinobacteridae.

Comparative genomic sequencing is shedding new light on bacterial identification, taxonomy and phylogeny. An in silico assessment of a core gene set necessary for cellular functioning was made to determine a consensus set of genes that would be useful for the identification, taxonomy and phylogeny of the species belonging to the subclass Actinobacteridae which contained two orders Actinomycetales and Bifidobacteriales. The subclass Actinobacteridae comprised about 85% of the actinobacteria families. The following recommended criteria were used to establish a comprehensive gene set; the gene should (i) be long enough to contain phylogenetically useful information, (ii) not be subject to horizontal gene transfer, (iii) be a single copy (iv) have at least two regions sufficiently conserved that allow the design of amplification and sequencing primers and (v) predict whole-genome relationships. We applied these constraints to 50 different Actinobacteridae genomes and made 1,224 pairwise comparisons of the genome conserved regions and gene fragments obtained by using Sequence VARiability Analysis Program (SVARAP), which allow designing the primers. Following a comparative statistical modeling phase, 3 gene fragments were selected, ychF, rpoB, and secY with R2>0.85. Selected sets of broad range primers were tested from the 3 gene fragments and were demonstrated to be useful for amplification and sequencing of 25 species belonging to 9 genera of Actinobacteridae. The intraspecies similarities were 96.3-100% for ychF, 97.8-100% for rpoB and 96.9-100% for secY among 73 strains belonging to 15 species of the subclass Actinobacteridae compare to 99.4-100% for 16S rRNA. The phylogenetic topology obtained from the combined datasets ychF+rpoB+secY was globally similar to that inferred from the 16S rRNA but with higher confidence. It was concluded that multi-locus sequence analysis using core gene set might represent the first consensus and valid approach for investigating the bacterial identification, phylogeny and taxonomy.

Mycobacterium phocaicum in therapy pool water.

We isolated Mycobacterium phocaicum, an emerging non-tuberculous species rarely identified in the respiratory tract and blood of patients, from the therapy pool water. Identification, confirmed by 16S rDNA and rpoB sequencing and phylogenetic analyses, disclosed a genotype 4. M. phocaicum should be added to the growing list of water-borne mycobacteria.

rpoB sequence-based identification of Mycobacterium avium complex species.

The Mycobacterium avium complex (MAC) comprises slowly growing mycobacteria responsible for opportunistic infections and zoonoses. The ability to speciate MAC isolates in the clinical microbiology laboratory is critical for determining the organism implicated in clinical disease and for epidemiological investigation of the source of infection. Investigation of a 711 bp variable fragment of rpoB flanked by the Myco-F/Myco-R primers found a 0.7-5.1 % divergence among MAC reference strains, with Mycobacterium chimaera and Mycobacterium intracellulare being the most closely related. Using a 0.7 % divergence cut-off, 83 % of 100 clinical isolates, which had been previously identified by phenotypic characteristics and 16S-23S rDNA intergenic spacer (ITS) probing, were identified as M. avium, 8 % as M. intracellulare and 2 % as M. chimaera. The uniqueness of seven isolates, exhibiting < 99.3 % rpoB sequence similarity with MAC reference strains, was confirmed by 16S rDNA, ITS and hsp65 sequencing and phylogenetic analyses. Partial rpoB gene sequencing using the Myco-F/Myco-R primers permits one-step identification of MAC isolates at the species level and the detection of potentially novel MAC species.