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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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Metabolic modulation reverses the antibiotic tolerance induced by lowiron and hypoxic conditions.Bacterial survival in the presence of the indicated antibiotics underhypoxic conditions (A, C, E, G) and in low iron media (B, D, F, H).Isoniazid (“INH”, 2 and 0.25 µg ml−1,A and B), streptomycin (“SMP”, 2 and 1 µgml−1, C and D), ciprofloxacin (“CIP”, 4and 1 µg ml−1, E and F), and ethambutol(“EMB”, 5 and 3 µg ml−1, G and H)were introduced into each culture. Antibiotics were added to the hypoxicvials after 14 d of culture. Means ± SD of two independentexperiments each performed in duplicate are shown.
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pbio-1001065-g003: Metabolic modulation reverses the antibiotic tolerance induced by lowiron and hypoxic conditions.Bacterial survival in the presence of the indicated antibiotics underhypoxic conditions (A, C, E, G) and in low iron media (B, D, F, H).Isoniazid (“INH”, 2 and 0.25 µg ml−1,A and B), streptomycin (“SMP”, 2 and 1 µgml−1, C and D), ciprofloxacin (“CIP”, 4and 1 µg ml−1, E and F), and ethambutol(“EMB”, 5 and 3 µg ml−1, G and H)were introduced into each culture. Antibiotics were added to the hypoxicvials after 14 d of culture. Means ± SD of two independentexperiments each performed in duplicate are shown.

Mentions: Since decreased metabolic activity generally correlates with lower antibioticefficacy, we speculated that TAG synthesis might contribute to the drug-tolerantphenotype induced by stress. We tested this hypothesis using in vitro conditionsthat trigger TAG accumulation. Indeed, we found that theΔtgs1 mutant remained significantly more sensitive to avariety of antibiotics under tolerance-inducing conditions such as hypoxia andiron limitation (Figure 3).The antibiotics used were chemically distinct and targeted diverse cellularpathways, suggesting that the general hypersensitivity of theΔtgs1 bacteria was due to a fundamental alteration incellular metabolism. As expected, the increased multidrug-susceptibility of theΔtgs1 mutant was much less pronounced under favorablegrowth conditions in which this gene is not induced (Figure S7).Under these conditions, the mutant was no more susceptible than wild type to anyof the drugs tested, except the fatty acid synthesis inhibitor, isoniazid (INH).We conclude that while TAG synthesis may influence INH sensitivity throughmultiple mechanisms, the multidrug susceptibility of theΔtgs1 mutant is due to a general increase in growthrate and/or metabolic activity. This conclusion was supported by the remarkableantibiotic sensitivity of the citA* strain that we observedin tolerance-inducing cultures (Figure 3). This strain was killed even more rapidly than theΔtgs1 mutant, verifying that metabolic rate is a majordeterminant of antibiotic susceptibility under these conditions.


Metabolic regulation of mycobacterial growth and antibiotic sensitivity.

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

Metabolic modulation reverses the antibiotic tolerance induced by lowiron and hypoxic conditions.Bacterial survival in the presence of the indicated antibiotics underhypoxic conditions (A, C, E, G) and in low iron media (B, D, F, H).Isoniazid (“INH”, 2 and 0.25 µg ml−1,A and B), streptomycin (“SMP”, 2 and 1 µgml−1, C and D), ciprofloxacin (“CIP”, 4and 1 µg ml−1, E and F), and ethambutol(“EMB”, 5 and 3 µg ml−1, G and H)were introduced into each culture. Antibiotics were added to the hypoxicvials after 14 d of culture. Means ± SD of two independentexperiments each performed in duplicate are shown.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-1001065-g003: Metabolic modulation reverses the antibiotic tolerance induced by lowiron and hypoxic conditions.Bacterial survival in the presence of the indicated antibiotics underhypoxic conditions (A, C, E, G) and in low iron media (B, D, F, H).Isoniazid (“INH”, 2 and 0.25 µg ml−1,A and B), streptomycin (“SMP”, 2 and 1 µgml−1, C and D), ciprofloxacin (“CIP”, 4and 1 µg ml−1, E and F), and ethambutol(“EMB”, 5 and 3 µg ml−1, G and H)were introduced into each culture. Antibiotics were added to the hypoxicvials after 14 d of culture. Means ± SD of two independentexperiments each performed in duplicate are shown.
Mentions: Since decreased metabolic activity generally correlates with lower antibioticefficacy, we speculated that TAG synthesis might contribute to the drug-tolerantphenotype induced by stress. We tested this hypothesis using in vitro conditionsthat trigger TAG accumulation. Indeed, we found that theΔtgs1 mutant remained significantly more sensitive to avariety of antibiotics under tolerance-inducing conditions such as hypoxia andiron limitation (Figure 3).The antibiotics used were chemically distinct and targeted diverse cellularpathways, suggesting that the general hypersensitivity of theΔtgs1 bacteria was due to a fundamental alteration incellular metabolism. As expected, the increased multidrug-susceptibility of theΔtgs1 mutant was much less pronounced under favorablegrowth conditions in which this gene is not induced (Figure S7).Under these conditions, the mutant was no more susceptible than wild type to anyof the drugs tested, except the fatty acid synthesis inhibitor, isoniazid (INH).We conclude that while TAG synthesis may influence INH sensitivity throughmultiple mechanisms, the multidrug susceptibility of theΔtgs1 mutant is due to a general increase in growthrate and/or metabolic activity. This conclusion was supported by the remarkableantibiotic sensitivity of the citA* strain that we observedin tolerance-inducing cultures (Figure 3). This strain was killed even more rapidly than theΔtgs1 mutant, verifying that metabolic rate is a majordeterminant of antibiotic susceptibility under these conditions.

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