Metabolic Regulation of Mycobacterial Growth and Antibiotic Sensitivity

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.

Isocitrate lyase mediates broad antibiotic tolerance in Mycobacterium tuberculosis

“…Despite intensive focus on the primary drug-target interaction and its maladaptive consequences, knowledge of the endogenous mechanisms used by bacteria to resist antibiotic activity is incomplete and centred chiefly around mechanisms associated with the drug-target interaction, such as drug efflux pumps and antibiotic-and/or target-modifying enzymes 3 . However, growing evidence has implicated a broader range of physiologic factors [7][8][9][10]27 .…”

“…More recent studies have begun to revise this view with the demonstration that even non-, or slowly, replicating bacteria could be rendered sensitive to antibiotics. Studies of Escherichia coli, Staphylococcus aureus and even Mtb have shown that the activity of many antibiotics: (i) is dependent on the activity of specific metabolic pathways, (ii) differs for replicating and nonreplicating populations and (iii) can be dissociated from growth rate 7,12,27 . In Mtb, it was shown that adaptation to hypoxia was accompanied by a redirection of metabolic flux away from the TCA cycle and towards the generation of triglycerides, whose inhibition resensitized Mtb to antibiotics in absence of growth 7 .…”

“…Recent work has expanded the scope of physiologic factors associated with antibiotic resistance to include broader bacterial stress responses, such as the SOS DNA stress response, heatshock response and oxidative stress response, as well as changes in metabolic state and activity [7][8][9][10][11][12] . These antibiotic-induced responses then contribute functionally to resistance.…”

Activity of 3-Ketosteroid 9α-Hydroxylase (KshAB) Indicates Cholesterol Side Chain and Ring Degradation Occur Simultaneously in Mycobacterium tuberculosis

“…KstD has previously been shown to catalyze the ⌬ 1 -dehydrogenation of 4-AD, 6 5␣-androstane-3,17-dione, 5␣-testosterone, and progesterone (31). Monitoring of the reaction by HPLC revealed a decrease in the 4-BNC-CoA peak and appearance of a new peak eluting at 18 min of Gradient B.…”

Rv0494 is a starvation-inducible, auto-regulatory FadR-like regulator from Mycobacterium tuberculosis

“…Although the events which initiate dormancy are not fully understood, hypoxia, nitric oxide and nutrient starvation are among the factors believed to have prominent roles in initiating and maintaining dormancy (Betts et al, 2002;Voskuil et al, 2003;Wayne & Sohaskey, 2001). During dormant stages, the major sources of energy are host-derived cholesterol and triglycerides (Baek et al, 2011;Pandey & Sassetti, 2008). This study aimed to characterize the starvation-inducible, lipid-responsive transcription factor Rv0494 from M. tuberculosis.…”