Genetic Requirements for the Survival of Tubercle Bacilli in Primates

Abstract

Background TB leads to the annual death of 1.7 million people. The failure of the BCG 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 Mtb to successfully infect and persist in mammalian lungs. Methods NHPs are arguably the best animal system to model critical aspects of human TB. We studied genes essential for growth/survival of Mtb in the lungs of NHPs experimentally exposed to aerosols of an Mtb transposon mutant library. Results Mutants in 108 Mtb genes (33.13% of all tested) were attenuated for in-vivo growth. Comparable studies have reported the attenuation of only ~6% of mutants in mice. The Mtb 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. Conclusions Our study highlights the various virulence-mechanisms employed by Mtb to overcome the hostile environment encountered during infection of primates. Prophylactic approaches aimed against bacterial factors which respond to such in-vivo stressors, have the potential to prevent infection at an early stage, thus likely reducing the extent of transmission of Mtb.

An Unbiased Genome-Wide Mycobacterium tuberculosis Gene Expression Approach To Discover Antigens Targeted by Human T Cells Expressed during Pulmonary Infection

“…A subsequent literature search revealed that almost all further selected IVE-TB proteins (14 of the 16) have been identified previously in M. tuberculosis proteomic studies, confirming the protein expression of the M. tuberculosis genes identified in our study (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57) (Table III). Indeed, we observed that M. tuberculosis- FIGURE 3.…”

DosS Is Required for the Complete Virulence of Mycobacterium tuberculosis in Mice with Classical Granulomatous Lesions

“…Lung tissue was fixed for hematoxylin-eosin histology and confocal microscopy (18)(19)(20)(21)(22). Ten images of each slide were used for analysis (Inform; PerkinElmer, Waltham, MA).…”

Genetic Strategies for Identifying New Drug Targets

“…The Mce4 gene cluster is homologous to genes first identified during studies of mycobacterial cell entry (41) and is essential for M. tuberculosis survival in mice (15), probably due to its role in cholesterol uptake by the bacterium (42). It was later shown to be required for survival of M. tuberculosis in the macaque model of tuberculosis (18). Cholesterol is therefore an important source of carbon for M. tuberculosis during infection (43), but it is also a source of a number of intermediates, such as catechols and propionyl-coenzyme A, which are toxic if not cleared by the cell (43-46).…”

“…Genes are regularly assessed for their contribution to virulence in the mouse model of infection, and multiple systematic assessments of gene essentiality both in vitro and in vivo have already been used to gain a global perspective (14)(15)(16)(17)(18)(19). As a result, there is already a growing body of knowledge about potential targets and metabolic pathways whose disruption should have a profound effect on Mycobacterium tuberculosis viability in vivo.…”

“…One way to populate the list of genes of interest in a meaningful way is to focus on conditionally essential genes whose function is interwoven with pathogenesis. For example, transposon mutagenesis techniques were used to study the animal models of infection (15)(16)(17)(18) and for the identification of genes required for survival in the macrophage (40). The results of these studies afford an eagle-eye view of the biological processes that are likely to be important during infection and provide important clues on the aspects of metabolism that should be investigated further as potential targets for intervention.…”