Einstein Contained Aerosol Pulmonizer (ECAP): Improved Biosafety for Multi-Drug Resistant (MDR) and Extensively Drug Resistant (XDR) Mycobacterium tuberculosis Aerosol Infection Studies

Generation of IL-3-Secreting CD4+ T Cells by Microbial Challenge at Skin and Mucosal Barriers

During Ag priming, naive CD4⁺ T cells differentiate into subsets with distinct patterns of cytokine expression that dictate to a major extent their functional roles in immune responses. We identified a subset of CD4⁺ T cells defined by secretion of IL-3 that was induced by Ag stimulation under conditions different from those associated with previously defined functional subsets. Using mouse models of bacterial and viral infections, we showed that IL-3–secreting CD4⁺ T cells were generated by infection at the skin and mucosa but not by infections introduced directly into the blood. Most IL-3–producing T cells coexpressed GM-CSF and other cytokines that define multifunctionality. Generation of IL-3–secreting T cells in vitro was dependent on IL-1 family cytokines and was inhibited by cytokines that induce canonical Th1 or Th2 cells. Our results identify IL-3–secreting CD4⁺ T cells as a potential functional subset that arises during priming of naive T cells in specific tissue locations.

Rational Design of Biosafety Level 2-Approved, Multidrug-Resistant Strains of Mycobacterium tuberculosis through Nutrient Auxotrophy

Multidrug-resistant (MDR) tuberculosis, defined as tuberculosis resistant to the two first-line drugs isoniazid and rifampin, poses a serious problem for global tuberculosis control strategies. Lack of a safe and convenient model organism hampers progress in combating the spread of MDR strains of Mycobacterium tuberculosis. We reasoned that auxotrophic MDR mutants of M. tuberculosis would provide a safe means for studying MDR M. tuberculosis without the need for a biosafety level 3 (BSL3) laboratory. Two different sets of triple auxotrophic mutants of M. tuberculosis were generated, which were auxotrophic for the nutrients leucine, pantothenate, and arginine or for leucine, pantothenate, and methionine. These triple auxotrophic strains retained their acid-fastness, their ability to generate both a drug persistence phenotype and drug-resistant mutants, and their susceptibility to plaque-forming mycobacterial phages. MDR triple auxotrophic mutants were obtained in a two-step fashion, selecting first for solely isoniazid-resistant or rifampin-resistant mutants. Interestingly, selection for isoniazid-resistant mutants of the methionine auxotroph generated isolates with single point mutations in katG, which encodes an isoniazid-activating enzyme, whereas similar selection using the arginine auxotroph yielded isoniazid-resistant mutants with large deletions in the chromosomal region containing katG. These M. tuberculosis MDR strains were readily sterilized by second-line tuberculosis drugs and failed to kill immunocompromised mice. These strains provide attractive candidates for M. tuberculosis biology studies and drug screening outside the BSL3 facility.

Elimination of Mycobacterium tuberculosis, the bacterium causing tuberculosis, requires enhanced understanding of its biology in order to identify new drugs against drug-susceptible and drug-resistant M. tuberculosis as well as uncovering novel pathways that lead to M. tuberculosis death. To circumvent the need for a biosafety level 3 (BSL3) laboratory when conducting research on M. tuberculosis, we have generated drug-susceptible and drug-resistant triple auxotrophic strains of M. tuberculosis suitable for use in a BSL2 laboratory. These strains originate from a double auxotrophic M. tuberculosis strain, H37Rv ΔpanCD ΔleuCD, which was reclassified as a BSL2 strain based on its lack of lethality in immunocompromised and immunocompetent mice. A third auxotrophy (methionine or arginine) was introduced via deletion of metA or argB, respectively, since M. tuberculosis ΔmetA and M. tuberculosis ΔargB are unable to survive amino acid auxotrophy and infect their host. The resulting triple auxotrophic M. tuberculosis strains retained characteristics of M. tuberculosis relevant for most types of investigations.

Plasticity of Mycobacterium tuberculosis NADH dehydrogenases and their role in virulence

Worldwide control of the tuberculosis (TB) epidemic has not been achieved, and the latest statistics show that the TB problem might be more endemic than previously thought. Although drugs and a TB vaccine are available, TB eradication faces the challenges of increasing occurrences of multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis (Mtb) strains. To forestall this trend, the development of drugs targeting novel pathways is actively pursued. Recently, enzymes of the electron transport chain (ETC) have been determined to be the targets of potent antimycobacterial drugs such as bedaquiline. We focused on the three NADH dehydrogenases (Ndh, NdhA, and Nuo) of the Mtb ETC with the purpose of defining their role and essentiality in Mtb Each NADH dehydrogenase was deleted in both virulent and BSL2-approved Mtb strains, from which the double knockouts ΔndhΔnuoAN and ΔndhAΔnuoAN were constructed. The ΔndhΔndhA double knockout could not be obtained, suggesting that at least one type II NADH dehydrogenase is required for Mtb growth. Δndh and ΔndhΔnuoAN showed growth defects in vitro and in vivo, susceptibility to oxidative stress, and redox alterations, while the phenotypes of ΔndhA, ΔnuoAN, and ΔndhAΔnuoAN were similar to the parental strain. Interestingly, although ΔnuoAN had no phenotype in vivo, ΔndhΔnuoAN was the most severely attenuated strain in mice, suggesting a key role for Nuo in vivo when Ndh is absent. We conclude that Ndh is the main NADH dehydrogenase of Mtb and that compounds that could target both Ndh and Nuo would be good candidates for TB drug development.

Animals devoid of pulmonary system as infection models in the study of lung bacterial pathogens

Biological disease models can be difficult and costly to develop and use on a routine basis. Particularly, in vivo lung infection models performed to study lung pathologies use to be laborious, demand a great time and commonly are associated with ethical issues. When infections in experimental animals are used, they need to be refined, defined, and validated for their intended purpose. Therefore, alternative and easy to handle models of experimental infections are still needed to test the virulence of bacterial lung pathogens. Because non-mammalian models have less ethical and cost constraints as a subjects for experimentation, in some cases would be appropriated to include these models as valuable tools to explore host-pathogen interactions. Numerous scientific data have been argued to the more extensive use of several kinds of alternative models, such as, the vertebrate zebrafish (Danio rerio), and non-vertebrate insects and nematodes (e.g., Caenorhabditis elegans) in the study of diverse infectious agents that affect humans. Here, we review the use of these vertebrate and non-vertebrate models in the study of bacterial agents, which are considered the principal causes of lung injury. Curiously none of these animals have a respiratory system as in air-breathing vertebrates, where respiration takes place in lungs. Despite this fact, with the present review we sought to provide elements in favor of the use of these alternative animal models of infection to reveal the molecular signatures of host-pathogen interactions.