Tryptophan Uptake By Mycobacterium tuberculosis H ₃₇ Rv: Effect of Rifampin and Ethambutol

Abstract

Uptake of radioactive tryptophan by Mycobacterium tuberculosis H 37 Rv grown in vitro and in vivo was investigated. K m values indicated low affinity, and sodium azide inhibited uptake. Rifampin at the minimal inhibitory concentration had no effect, whereas ethambutol inhibited uptake only in the bacilli grown under in vitro conditions. The significance of these results is discussed.

Mycobacterial cell wall: Structure and role in natural resistance to antibiotics

“…Mycobacterial cell wall has long been suspected to act as a permeation barrier for antibiotics Some redirect data were available For example, the antibiotic efficacy increased when detergents such as Tween were added to culture media [1l], or when the cell wall structure became defective due to mutations [12] Furthermore, ammoglycosldes were shown to be more actwe on ribosomes in cell extracts than on intact mycobactenal cells, suggesting the role of a cell surface barrier [11] In specms producing intrinsic fl-lactamase, the enzyme is cryptic, and the hydrolysis of /3-1actams measured with disrupted cells is far faster than that measured in intact cells [13] Recent data also show a synergistic effect between various agents and those agents that are known to inhibit the synthesis of cell wall components, such as ethambutol [14] In spite of these largely quahtatwe results, there was no quantitative measurement of the permeability of mycobacterIal cell wall, until our study [15] We used the method introduced for estimation of outer membrane permeability in Gram-negative bacteria [16] We measured the rate of hydrolysis of/3-1actams by intact bacterial cells, and calculated the cell wall permeability by assuming that drug molecules first diffuse through the cell wall (following Flck's first law of diffusion) and then are hydrolyzed by perlplasmlc /3-1actamase (following the Mlchaehs-Menten kinetics) For this method, cells should exist as unicellular dispersions in contact with the medium A strain of M chelonae was chosen because ~t produced homogeneous suspensions without the use of detergents, and because it produced a/3-1actamase of sufficmntly high activity which did not leak out into the medium The cell wall permeability to cephalosporins measured in this strain was indeed very low, and was about three orders of magnitude lower than that of E cob outer membrane, and ten times lower than the permeability of the notoriously impermeable P aerugtnosa outer membrane (Fig 2) Another approach was that of studying the kinetics of nutrient uptake If we assume that nutrient molecules are taken up by high-affinity formed as m [15], utlhzmg the transport data from [19] and from papers cited in [18] more slowly than through the outer membrane of E cob [15] (Fig 2) M chelonae, chosen as a model because its propemes were convenient for our assay, happens to be one of the most drug-res]stant species among mycobacter]a Thus ]t becomes Important to study the cell wall permeabd]ty of other mycobactenal species M smegmatts, widely used m studies of molecular biology, was found to show about ten-fold higher permeabd]ty to /3-1actams, by us]ng an assay slmdar to that used for M chelonae [17] The assay had to be modified for M tuberculosts, which has a stronger tendency to aggregate Use of th~s modified assay showed that M tuberculosts H37Ra was more permeable, by a factor of nearly ten, than the M chelonae stram studied earher (E Y Rosenberg and H N]ka]do, unpubhshed results) These results are consistent with our knowledge that atypical species, such as M chelonae, are usually more resistant to a number ...…”

Gut Microbiota Metabolite Indole Propionic Acid Targets Tryptophan Biosynthesis in Mycobacterium tuberculosis

“…As the standard mycobacterium broth Middlebrook 7H9 does not contain Trp, M. tuberculosis needs to synthesize this amino acid to grow. If IPA acts via blocking Trp synthesis by inhibiting TrpE, exogenous supply of anthranilate or Trp should eliminate the inhibitory effect of IPA (12, 13, 24, 25). M. tuberculosis cultures grown in medium without any supplement or with exogenously supplied anthranilate or Trp were treated with increasing IPA concentrations, and the optical density at 600 nm (OD 600 ) was measured.…”

5-Fluoroindole Reduces the Bacterial Burden in a Murine Model of Mycobacterium tuberculosis Infection

“…No inhibition of Mtb H37Rv strain growth was observed for 5-fluorotryptophan at concentrations up to 20 μg/mL (approximately 90 μM) under the same experimental conditions employed by the other indole-containing chemical compounds presented in Table 1 . This lack of growth inhibition may be ascribed to both the rather large Michaelis–Menten constant ( K M = 1.25 mM) for the tryptophan transport system of Mtb H37Rv strain 27 and the increased polarity of 5-fluorotryptophan (reduced passive diffusion). The results for 5-FI.HCl suggest that this compound may be a promising drug candidate for treating TB with the potential to inhibit drug-susceptible and drug-resistant Mtb strains.…”