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Genetic requirements for the survival of tubercle bacilli in primates.

ABSTRACT: Tuberculosis (TB) leads to the death of 1.7 million people annually. The failure of the bacille Calmette-Guérin vaccine, synergy between AIDS and TB, and the emergence of drug resistance have worsened this situation. It is imperative to delineate the mechanisms employed by Mycobacterium tuberculosis to successfully infect and persist in mammalian lungs.Nonhuman primates (NHPs) are arguably the best animal system to model critical aspects of human TB. We studied genes essential for growth and survival of M. tuberculosis in the lungs of NHPs experimentally exposed to aerosols of an M. tuberculosis transposon mutant library.Mutants in 108 M. tuberculosis genes (33.13% of all genes tested) were attenuated for in vivo growth. Comparable studies have reported the attenuation of only approximately 6% of mutants in mice. The M. tuberculosis mutants attenuated for in vivo survival in primates were involved in the transport of various biomolecules, including lipid virulence factors; biosynthesis of cell-wall arabinan and peptidoglycan; DNA repair; sterol metabolism; and mammalian cell entry.Our study highlights the various virulence mechanisms employed by M. tuberculosis to overcome the hostile environment encountered during infection of primates. Prophylactic approaches aimed against bacterial factors that respond to such in vivo stressors have the potential to prevent infection at an early stage, thus likely reducing the extent of transmission of M. tuberculosis.

SUBMITTER: Dutta NK

PROVIDER: S-EPMC2862080 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Smooth Tubercle Bacilli: Neglected Opportunistic Tropical Pathogens.

Project description:Smooth tubercle bacilli (STB) including "Mycobacterium canettii" are members of the Mycobacterium tuberculosis complex (MTBC), which cause non-contagious tuberculosis in human. This group comprises <100 isolates characterized by smooth colonies and cordless organisms. Most STB isolates have been obtained from patients exposed to the Republic of Djibouti but seven isolates, including the three seminal ones obtained by Georges Canetti between 1968 and 1970, were recovered from patients in France, Madagascar, Sub-Sahara East Africa, and French Polynesia. STB form a genetically heterogeneous group of MTBC organisms with large 4.48?±?0.05?Mb genomes, which may link Mycobacterium kansasii to MTBC organisms. Lack of inter-human transmission suggested a yet unknown environmental reservoir. Clinical data indicate a respiratory tract route of contamination and the digestive tract as an alternative route of contamination. Further epidemiological and clinical studies are warranted to elucidate areas of uncertainty regarding these unusual mycobacteria and the tuberculosis they cause.

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NAD+ auxotrophy is bacteriocidal for the tubercle bacilli.

Project description:The human tubercle bacillus Mycobacterium tuberculosis can synthesize NAD(+) using the de novo biosynthesis pathway or the salvage pathway. The salvage pathway of the bovine tubercle bacillus Mycobacterium bovis was reported defective due to a mutation in the nicotinamidase PncA. This defect prevents nicotinic acid secretion, which is the basis for the niacin test that clinically distinguishes M. bovis from M. tuberculosis. Surprisingly, we found that the NAD(+)de novo biosynthesis pathway (nadABC) can be deleted from M. bovis, demonstrating a functioning salvage pathway. M. bovisDeltanadABC fails to grow in mice, whereas M. tuberculosisDeltanadABC grows normally in mice, suggesting that M. tuberculosis can acquire nicotinamide from its host. The introduction of M. tuberculosis pncA into M. bovisDeltanadABC is sufficient to fully restore growth in a mouse, proving that the functional salvage pathway enables nicotinamide acquisition by the tubercle bacilli. This study demonstrates that NAD(+) starvation is a cidal event in the tubercle bacilli and confirms that enzymes common to the de novo and salvage pathways may be good drug targets.

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Resuscitation-promoting factors reveal an occult population of tubercle Bacilli in Sputum.

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Insights into the evolutionary history of tubercle bacilli as disclosed by genetic rearrangements within a PE_PGRS duplicated gene pair.

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RNA sequencing provides exquisite insight into the manipulation of the alveolar macrophage by tubercle bacilli

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Project description:Despite the importance of tuberculosis as a public health problem, we know relatively little about the molecular mechanisms used by the causative organism, Mycobacterium tuberculosis, to persist in the host. To define these mechanisms, we have mutated virtually every nonessential gene of M. tuberculosis and determined the effect disrupting each gene on the growth rate of this pathogen during infection. A total of 194 genes that are specifically required for mycobacterial growth in vivo were identified. The behavior of these mutants provides a detailed view of the changing environment that the bacterium encounters as infection proceeds. A surprisingly large fraction of these genes are unique to mycobacteria and closely related species, indicating that many of the strategies used by this unusual group of organisms are fundamentally different from other pathogens

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RNA sequencing provides exquisite insight into the manipulation of the alveolar macrophage by tubercle bacilli.

Project description:Mycobacterium bovis, the agent of bovine tuberculosis, causes an estimated $3 billion annual losses to global agriculture due, in part, to the limitations of current diagnostics. Development of next-generation diagnostics requires a greater understanding of the interaction between the pathogen and the bovine host. Therefore, to explore the early response of the alveolar macrophage to infection, we report the first application of RNA-sequencing to define, in exquisite detail, the transcriptomes of M. bovis-infected and non-infected alveolar macrophages from ten calves at 2, 6, 24 and 48?hours post-infection. Differentially expressed sense genes were detected at these time points that revealed enrichment of innate immune signalling functions, and transcriptional suppression of host defence mechanisms (e.g., lysosome maturation). We also detected differentially expressed natural antisense transcripts, which may play a role in subverting innate immune mechanisms following infection. Furthermore, we report differential expression of novel bovine genes, some of which have immune-related functions based on orthology with human proteins. This is the first in-depth transcriptomics investigation of the alveolar macrophage response to the early stages of M. bovis infection and reveals complex patterns of gene expression and regulation that underlie the immunomodulatory mechanisms used by M. bovis to evade host defence mechanisms.

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Improved polyacrylamide-based artificial sputum with formalin-fixed tubercle bacilli for training of tuberculosis microscopists.

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