Mycobacterium tuberculosis claims more human lives each year than any other bacterial pathogen. Infection is maintained in spite of acquired immunity and resists eradication by antimicrobials. Despite an urgent need for new therapies targeting persistent bacteria, our knowledge of bacterial metabolism throughout the course of infection remains rudimentary. Here we report that persistence of M. tuberculosis in mice is facilitated by isocitrate lyase (ICL), an enzyme essential for the metabolism of fatty acids. Disruption of the icl gene attenuated bacterial persistence and virulence in immune-competent mice without affecting bacterial growth during the acute phase of infection. A link between the requirement for ICL and the immune status of the host was established by the restored virulence of delta icl bacteria in interferon-gamma knockout mice. This link was apparent at the level of the infected macrophage: Activation of infected macrophages increased expression of ICL, and the delta icl mutant was markedly attenuated for survival in activated but not resting macrophages. These data suggest that the metabolism of M. tuberculosis in vivo is profoundly influenced by the host response to infection, an observation with important implications for the treatment of chronic tuberculosis.

Mycobacterium tuberculosis resides within the phagocytes of its host. It ensures its continued survival through arresting the normal maturation of its phagosome, which is retained within the early endosomal system of the macrophage. Although individual bacterial components have been shown to modulate phagosome biogenesis, the mechanism(s) active in live, intact bacteria remain elusive. We have developed a genetic screen that facilitates the isolation of mutants defective in arresting the maturation of their phagosomes. Macrophages were incubated with iron-dextran that was chased into lysosomes. The cells were subsequently infected with M. tuberculosis from a library of transposon-mutagenized bacteria. After four rounds of enrichment, the majority of mutants isolated were unable to prevent acidification of their phagosomes and were attenuated for intracellular survival. The genes affected range in function from those with no known homologues to putative transporters and lipid synthesis enzymes. Further characterization of these bacteria is needed. In addition to clarifying the processes active in modulation of phagosome biogenesis by M. tuberculosis, this screen may be applicable to other pathogens that restrict the maturation of their phagosome. P athogenic Mycobacterium spp. are known to reside in vacuoles that fail to exhibit the normal progression of phagosomes to phagolysosomes. Studies from several groups (1-3) have demonstrated that the phagosomes containing these bacilli retain many of the characteristics of early endosomes and remain accessible to material internalized by means of the rapid recycling endosomal system.The normal progression of phagosomes after internalization of inert particles by phagocytes involves the transient acquisition of the GTPase rab5, phosphorylation of phosphatidylinositol (PI) to generate PI-3-phosphate (PI3P) by the PI kinase VPS34, and accumulation of the PI3P-binding protein early endosome autoantigen 1 (EEA1) (4-7). As the association with EEA1 diminishes, phagosomes show increased accumulation of rab7 and increased fusion with lysosomes. Within the lumen of phagosomes, one observes increased acidification and the accumulation of lysosomal hydrolases that are processed into their active forms as the environment within phagosomes becomes increasingly hydrolytic. In contrast, the phagosomes containing pathogenic Mycobacterium spp. fail to acidify below pH 6.2 (8, 9), remain positive for the early endosomal GTPase rab5 (10-12), and do not acquire EEA1 (13,14). Despite the extensive documentation of the aberrant retention of a range of host proteins, these studies do not provide an explanation of how the bacterium achieves this process of arrest.Several mechanisms have been proposed for this phenomenon, including the effects of ammonia production (15), the close apposition between the bacterium and its vacuole membrane (16), the ability of surface lipids such as lipoarabinomannan (LAM) and cord factor to inhibit vesicular fusion (13,14,17), and the activity of a bacterial ser...

On the basis of safety and efficacy, eVLPs represent a promising filovirus vaccine for use in humans.

Currently, no vaccines or therapeutics are licensed to counter Ebola or Marburg viruses, highly pathogenic filoviruses that are causative agents of viral hemorrhagic fever. Here we show that administration of positively charged phosphorodiamidate morpholino oligomers (PMOplus), delivered by various dosing strategies initiated 30-60 min after infection, protects>60% of rhesus monkeys against lethal Zaire Ebola virus (ZEBOV) and 100% of cynomolgus monkeys against Lake Victoria Marburg virus (MARV) infection. PMOplus may be useful for treating these and other highly pathogenic viruses in humans.