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Metabolic regulation of mycobacterial growth and antibiotic sensitivity.

Baek SH, Li AH, Sassetti CM - PLoS Biol. (2011)

Bottom Line: This pathway plays a causal role in reducing growth and antibiotic efficacy by redirecting cellular carbon fluxes away from the tricarboxylic acid cycle.Mutants in which this metabolic switch is disrupted are unable to arrest their growth in response to stress and remain sensitive to antibiotics during infection.Thus, this regulatory pathway contributes to antibiotic tolerance in vivo, and its modulation may represent a novel strategy for accelerating TB treatment.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.

ABSTRACT
Treatment of chronic bacterial infections, such as tuberculosis (TB), requires a remarkably long course of therapy, despite the availability of drugs that are rapidly bacteriocidal in vitro. This observation has long been attributed to the presence of bacterial populations in the host that are "drug-tolerant" because of their slow replication and low rate of metabolism. However, both the physiologic state of these hypothetical drug-tolerant populations and the bacterial pathways that regulate growth and metabolism in vivo remain obscure. Here we demonstrate that diverse growth-limiting stresses trigger a common signal transduction pathway in Mycobacterium tuberculosis that leads to the induction of triglyceride synthesis. This pathway plays a causal role in reducing growth and antibiotic efficacy by redirecting cellular carbon fluxes away from the tricarboxylic acid cycle. Mutants in which this metabolic switch is disrupted are unable to arrest their growth in response to stress and remain sensitive to antibiotics during infection. Thus, this regulatory pathway contributes to antibiotic tolerance in vivo, and its modulation may represent a novel strategy for accelerating TB treatment.

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Modulating carbon fluxes reverses the antibiotic tolerance inducedduring infection.Mice were infected via the aerosol route with the indicated bacterialstrains. Total bacterial burden in the spleens (A, C, E) and lungs (B,D, F) is shown. Mice were treated at the indicated times with isoniazid(“INH”, A, B), ethambutol (“EMB”, C, D), orisoniazid plus pyrazinamide (“INH+PZA”, E, F). Dottedline represents the detection limit of the experiment. “ND”indicates no colonies detected. ND* indicates two colonies weredetected but neither retained the citA overexpressionplasmid. Means ± SD from three to five mice are shown.
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pbio-1001065-g004: Modulating carbon fluxes reverses the antibiotic tolerance inducedduring infection.Mice were infected via the aerosol route with the indicated bacterialstrains. Total bacterial burden in the spleens (A, C, E) and lungs (B,D, F) is shown. Mice were treated at the indicated times with isoniazid(“INH”, A, B), ethambutol (“EMB”, C, D), orisoniazid plus pyrazinamide (“INH+PZA”, E, F). Dottedline represents the detection limit of the experiment. “ND”indicates no colonies detected. ND* indicates two colonies weredetected but neither retained the citA overexpressionplasmid. Means ± SD from three to five mice are shown.

Mentions: Induction of the tgs1 gene and TAG accumulation occur duringinfection [20], and TCA activity appears to be limited in thisenvironment [25].Therefore, we next investigated whether TCA limitation by TAG synthesis was alsorequired for antibiotic tolerance in vivo. The Δtgs1mutation did not overtly disrupt the physiology of the bacterium in vivo, asonly subtle defects in bacterial viability were observed in mice infected withthe mutant (Figure S8). Despite this apparently normal behavior, the metabolicstate of the mutant was clearly different from wild type, as theΔtgs1 strain remained significantly more sensitive toseveral antibiotic regimens targeting different cellular functions (Figure 4). Consistent with acentral role for TCA activity in antibiotic tolerance in vivo, we found thatoverexpressing citrate synthase had a more pronounced effect. ThecitA* strain displayed a modest growth or survivaldefect in mice (Figures 4A,Band S8),indicating that increased TCA flux under these conditions decreased overallfitness. More importantly, this strain remained even more sensitive toantibiotics during infection than the Δtgs1 mutant, as wehad previously observed under in vitro stress conditions. After 28 d ofmonotherapy, the number of viable wild bacteria had only decreased 20-fold,while the number of viable citA overexpressors was reducedbelow the limit of detection (Figure 4A,B).


Metabolic regulation of mycobacterial growth and antibiotic sensitivity.

Baek SH, Li AH, Sassetti CM - PLoS Biol. (2011)

Modulating carbon fluxes reverses the antibiotic tolerance inducedduring infection.Mice were infected via the aerosol route with the indicated bacterialstrains. Total bacterial burden in the spleens (A, C, E) and lungs (B,D, F) is shown. Mice were treated at the indicated times with isoniazid(“INH”, A, B), ethambutol (“EMB”, C, D), orisoniazid plus pyrazinamide (“INH+PZA”, E, F). Dottedline represents the detection limit of the experiment. “ND”indicates no colonies detected. ND* indicates two colonies weredetected but neither retained the citA overexpressionplasmid. Means ± SD from three to five mice are shown.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3101192&req=5

pbio-1001065-g004: Modulating carbon fluxes reverses the antibiotic tolerance inducedduring infection.Mice were infected via the aerosol route with the indicated bacterialstrains. Total bacterial burden in the spleens (A, C, E) and lungs (B,D, F) is shown. Mice were treated at the indicated times with isoniazid(“INH”, A, B), ethambutol (“EMB”, C, D), orisoniazid plus pyrazinamide (“INH+PZA”, E, F). Dottedline represents the detection limit of the experiment. “ND”indicates no colonies detected. ND* indicates two colonies weredetected but neither retained the citA overexpressionplasmid. Means ± SD from three to five mice are shown.
Mentions: Induction of the tgs1 gene and TAG accumulation occur duringinfection [20], and TCA activity appears to be limited in thisenvironment [25].Therefore, we next investigated whether TCA limitation by TAG synthesis was alsorequired for antibiotic tolerance in vivo. The Δtgs1mutation did not overtly disrupt the physiology of the bacterium in vivo, asonly subtle defects in bacterial viability were observed in mice infected withthe mutant (Figure S8). Despite this apparently normal behavior, the metabolicstate of the mutant was clearly different from wild type, as theΔtgs1 strain remained significantly more sensitive toseveral antibiotic regimens targeting different cellular functions (Figure 4). Consistent with acentral role for TCA activity in antibiotic tolerance in vivo, we found thatoverexpressing citrate synthase had a more pronounced effect. ThecitA* strain displayed a modest growth or survivaldefect in mice (Figures 4A,Band S8),indicating that increased TCA flux under these conditions decreased overallfitness. More importantly, this strain remained even more sensitive toantibiotics during infection than the Δtgs1 mutant, as wehad previously observed under in vitro stress conditions. After 28 d ofmonotherapy, the number of viable wild bacteria had only decreased 20-fold,while the number of viable citA overexpressors was reducedbelow the limit of detection (Figure 4A,B).

Bottom Line: This pathway plays a causal role in reducing growth and antibiotic efficacy by redirecting cellular carbon fluxes away from the tricarboxylic acid cycle.Mutants in which this metabolic switch is disrupted are unable to arrest their growth in response to stress and remain sensitive to antibiotics during infection.Thus, this regulatory pathway contributes to antibiotic tolerance in vivo, and its modulation may represent a novel strategy for accelerating TB treatment.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.

ABSTRACT
Treatment of chronic bacterial infections, such as tuberculosis (TB), requires a remarkably long course of therapy, despite the availability of drugs that are rapidly bacteriocidal in vitro. This observation has long been attributed to the presence of bacterial populations in the host that are "drug-tolerant" because of their slow replication and low rate of metabolism. However, both the physiologic state of these hypothetical drug-tolerant populations and the bacterial pathways that regulate growth and metabolism in vivo remain obscure. Here we demonstrate that diverse growth-limiting stresses trigger a common signal transduction pathway in Mycobacterium tuberculosis that leads to the induction of triglyceride synthesis. This pathway plays a causal role in reducing growth and antibiotic efficacy by redirecting cellular carbon fluxes away from the tricarboxylic acid cycle. Mutants in which this metabolic switch is disrupted are unable to arrest their growth in response to stress and remain sensitive to antibiotics during infection. Thus, this regulatory pathway contributes to antibiotic tolerance in vivo, and its modulation may represent a novel strategy for accelerating TB treatment.

Show MeSH
Related in: MedlinePlus