Rifamycin action on RNA polymerase in antibiotic-tolerant Mycobacterium tuberculosis results in differentially detectable populations.

Mycobacterium tuberculosis (Mtb) encounters stresses during the pathogenesis and treatment of tuberculosis (TB) that can suppress replication of the bacteria and render them phenotypically tolerant to most available drugs. Where studied, the majority of Mtb in the sputum of most untreated subjects with active TB have been found to be nonreplicating by the criterion that they do not grow as colony-forming units (cfus) when plated on agar. However, these cells are viable because they grow when diluted in liquid media. A method for generating such "differentially detectable" (DD) Mtb in vitro would aid studies of the biology and drug susceptibility of this population, but lack of independent confirmation of reported methods has contributed to skepticism about their existence. Here, we identified confounding artifacts that, when avoided, allowed development of a reliable method of producing cultures of ≥90% DD Mtb in starved cells. We then characterized several drugs according to whether they contribute to the generation of DD Mtb or kill them. Of the agents tested, rifamycins led to DD Mtb generation, an effect lacking in a rifampin-resistant strain with a mutation in rpoB, which encodes the canonical rifampin target, the ß subunit of RNA polymerase. In contrast, thioridazine did not generate DD Mtb from starved cells but killed those generated by rifampin.

N-methylation of a bactericidal compound as a resistance mechanism in Mycobacterium tuberculosis.

The rising incidence of antimicrobial resistance (AMR) makes it imperative to understand the underlying mechanisms. Mycobacterium tuberculosis (Mtb) is the single leading cause of death from a bacterial pathogen and estimated to be the leading cause of death from AMR. A pyrido-benzimidazole, 14, was reported to have potent bactericidal activity against Mtb. Here, we isolated multiple Mtb clones resistant to 14. Each had mutations in the putative DNA-binding and dimerization domains of rv2887, a gene encoding a transcriptional repressor of the MarR family. The mutations in Rv2887 led to markedly increased expression of rv0560c. We characterized Rv0560c as an S-adenosyl-L-methionine-dependent methyltransferase that N-methylates 14, abolishing its mycobactericidal activity. An Mtb strain lacking rv0560c became resistant to 14 by mutating decaprenylphosphoryl-ß-d-ribose 2-oxidase (DprE1), an essential enzyme in arabinogalactan synthesis; 14 proved to be a nanomolar inhibitor of DprE1, and methylation of 14 by Rv0560c abrogated this activity. Thus, 14 joins a growing list of DprE1 inhibitors that are potently mycobactericidal. Bacterial methylation of an antibacterial agent, 14, catalyzed by Rv0560c of Mtb, is a previously unreported mechanism of AMR.

Oxidative damage and delayed replication allow viable Mycobacterium tuberculosis to go undetected.

"Viable but nonculturable" states of bacteria pose challenges for environmental and clinical microbiology, but their biological mechanisms remain obscure. Mycobacterium tuberculosis (Mtb), the leading cause of death from infection until the coronavirus disease 2019 pandemic, affords a notable example of this phenotype. Mtb can enter into a "differentially detectable" (DD) state associated with phenotypic antimicrobial resistance. In this state, Mtb cells are viable but undetectable as colony-forming units. We found that Mtb cells enter the DD state when they undergo sublethal oxidative stress that damages their DNA, proteins, and lipids. In addition, their replication process is delayed, allowing time for repair. Mycobacterium bovis and its derivative, BCG, fail to enter the DD state under similar conditions. These findings have implications for tuberculosis latency, detection, relapse, treatment monitoring, and development of regimens that overcome phenotypic antimicrobial resistance.

FK506 as an adjuvant of tolerogenic DNA vaccination for the prevention of experimental autoimmune encephalomyelitis.

BACKGROUND: DNA vaccination is a strategy that has been developed primarily to elicit protective immunity against infection and cancer. METHODS: DNA vaccine was used, in conjunction with an immunosuppressant, to tolerize harmful autoimmunity. RESULTS: Immunization of C57BL/6 mice with MOG(35-55), a myelin oligodendrocyte glycoprotein-derived peptide, and FK506 (Tacrolimus) as a tolerogenic adjuvant stimulated regulatory dendritic cells, induced antigen-specific regulatory T cells (Treg), and protected the animals from subsequent induction of experimental autoimmune encephalomyelitis (EAE). After EAE induction, there were fewer lymphocytes, including fewer T helper 17 cells, and more Treg infiltrating the spinal cord in the immunized mice compared to in control mice. Furthermore, at the peak of the EAE manifestation, CD4 T cells in the immunized mice showed decreased expression of interferon-gamma and interleukin (IL)-17, but not IL-4, in treated mice. CONCLUSIONS: DNA vaccination, when applied with an immunosuppressant as adjuvant, can induce antigen-specific tolerance and prevent autoimmune disease.

A genetically encoded reporter for real-time imaging of cofilin-actin rods in living neurons.

Filament bundles (rods) of cofilin and actin (1:1) form in neurites of stressed neurons where they inhibit synaptic function. Live-cell imaging of rod formation is hampered by the fact that overexpression of a chimera of wild type cofilin with a fluorescent protein causes formation of spontaneous and persistent rods, which is exacerbated by the photostress of imaging. The study of rod induction in living cells calls for a rod reporter that does not cause spontaneous rods. From a study in which single cofilin surface residues were mutated, we identified a mutant, cofilinR21Q, which when fused with monomeric Red Fluorescent Protein (mRFP) and expressed several fold above endogenous cofilin, does not induce spontaneous rods even during the photostress of imaging. CofilinR21Q-mRFP only incorporates into rods when they form from endogenous proteins in stressed cells. In neurons, cofilinR21Q-mRFP reports on rods formed from endogenous cofilin and induced by all modes tested thus far. Rods have a half-life of 30-60 min upon removal of the inducer. Vesicle transport in neurites is arrested upon treatments that form rods and recovers as rods disappear. CofilinR21Q-mRFP is a genetically encoded rod reporter that is useful in live cell imaging studies of induced rod formation, including rod dynamics, and kinetics of rod elimination.