Inhibition of synthesis of arabinogalactan by ethambutol in Mycobacterium smegmatis

Abstract

Ethambutol at 3.0 ,ug/ml inhibited the transfer of label from D- ['4C]glucose into the D-arabinose residue of arabinogalactan in whole cells of a drug-susceptible strain of Mycobacterium smegmatis. This inhibition began almost immediately after exposure of the cells to the drug. When drug-resistant M. smegmatis was used in a similar experiment, no such drug inhibition was detected. A much higher concentration of ethambutol (>50 ,ug/ml) was required to show this inhibition. The drug also inhibited synthesis of arabinose-containing oligosaccharides when a cell-free enzyme system was used. These results suggest that the site of action of ethambutol is somewhere on the pathway between the conversion of D-glucose to D-arabinose and the transfer of arabinose into arabinogalactan. The primary mode of action of ethambutol appears to be inhibition of arabinogalactan synthesis.Ethambutol is an effective and very specific drug used in combination with isoniazid to treat tuberculosis (8,9,17,18 smegmatis were used in this study (10). The ethambutolsusceptible M. smegmatis was an in-house strain of the Mycobacteriology Laboratory, Centers for Disease Control, Atlanta, Ga., and the ethambutol-resistant mutant was derived from this parent susceptible strain. The cells used to prepare cell extracts and to isolate the arabinogalactan and arabinomannan were grown in glycerol-alanine-salts medium (16) in a 28-liter New Brunswick fermentor (New Brunswick Scientific Co., Inc., Edison, N.J.) at 37°C for 24 h. Cells of M. smegmatis used to determine the in vivo synthesis of polysaccharides were grown in supplemented Middlebrook 7H9 broth (Difco Laboratories, Detroit, Mich.) at 37°C with shaking (11) to an A650 of 0.05 (ca. 2.5 x 106 CFU/ml). The albumin-dextrose enrichment was omitted, and 0.2% glycerol and 0.05% Tween 80 (Sigma Chemical Co., St. Louis, Mo.) were substituted.Preparation of cell-free enzyme system for synthesis of arabinose-containing oligosaccharides. Harvested cells of drug-susceptible M. smegmatis (25 g, wet weight) were suspended in 25 ml of 0.05 M potassium phosphate buffer, pH 7.0, and sonicated at full power in a Branson sonifier at 0 to 10°C for 7 min. The suspension was centrifuged at 10,000 x g for 30 min, and the turbid supernatant was recovered. This supernatant was recentrifuged under the same conditions as before to yield the 10,000 x g supernatant fraction. This preparation, containing about 43 mg of protein per ml as determined by the biuret method, was used to study the effects of ethambutol on the cell-free synthesis of arabinosecontaining oligosaccharides.Purification of arabinogalactan from commercial source. To a solution of plant arabinogalactan (1.0 g; K and K Laboratories, Inc., Plainview, N.Y.) in 20 ml of water, 24.4 ml of ethanol was added, and the mixture was centrifuged at 500 x g for 10 min. The dark brown residue was discarded; 100 ml of ethanol was added to the supernatant, which was then mixed well and centrifuged. The resulting residue, which 1493

Fluorescent Phospholipid Analogs as Microscopic Probes for Detection of the Mycolic Acid-Containing Layer inCorynebacterium glutamicum: Detecting Alterations in the Mycolic Acid-Containing Layer Following Ethambutol Treatment

“…By inhibiting arabinogalactan synthesis, EMB prevents formation of its covalently-bound mycolate layer. 11,12,27,31) The visible effects of EMB on mycolate-layer formation were observed mainly at cell division planes and cell poles (Fig. 2).…”

Dual Targeting of Cell Wall Precursors by Teixobactin Leads to Cell Lysis

“…Mycobacterium has a unique cell wall structure composed of arabinogalactan, peptidoglycan, and mycolic acid (42). The mechanism of ethambutol, an antituberculosis agents, is inhibition of arabinogalactan biosynthesis (43). Recently, it was reported that the inhibitor of WecA, which is the ortholog of TarO and is involved in arabinogalactan biosynthesis, has good antitubercular activity (44).…”

Antimycobacterial Activity Some Different Lamiaceae Plant Extracts Containing Flavonoids and Other Phenolic Compounds

“…EMB has a bacteriostatic effect and interferes with mycolic acid synthesis, phospholipid metabolism, and arabinogalactan synthesis (Kilburn et al, 1977;Takayama & Kilburn, 1989) and affects nucleic acid metabolism (Forbes et al,, 1965). EMB has synergistic actions, when combined with other agents, against Mycobacterium avium (Inderlied and Salfinger, 1995).…”