Effects of isoniazid on the composition of mycobacteria, with particular reference to soluble carbohydrates and related substances

CPMAS NMR platform for direct compositional analysis of mycobacterial cell-wall complexes and whole cells

Tuberculosis and non-tuberculosis mycobacterial infections are rising each year and often result in chronic incurable disease. Important antibiotics target cell-wall biosynthesis, yet some mycobacteria are alarmingly resistant or tolerant to currently available antibiotics. This resistance is often attributed to assumed differences in composition of the complex cell wall of different mycobacterial strains and species. However, due to the highly crosslinked and insoluble nature of mycobacterial cell walls, direct comparative determinations of cell-wall composition pose a challenge to analysis through conventional biochemical analyses. We introduce an approach to directly observe the chemical composition of mycobacterial cell walls using solid-state NMR spectroscopy. 13C CPMAS spectra are provided of individual components (peptidoglycan, arabinogalactan, and mycolic acids) and of in situ cell-wall complexes. We assigned the spectroscopic contributions of each component in the cell-wall spectrum. We uncovered a higher arabinogalactan-to-peptidoglycan ratio in the cell wall of M. abscessus, an organism noted for its antibiotic resistance, relative to M. smegmatis. Furthermore, differentiating influences of different types of cell-wall targeting antibiotics were observed in spectra of antibiotic-treated whole cells. This platform will be of value in evaluating cell-wall composition and antibiotic activity among different mycobacteria and in considering the most effective combination treatment regimens.

Real-time monitoring of live mycobacteria with a microfluidic acoustic-Raman platform

Tuberculosis (TB) remains a leading cause of death worldwide. Lipid rich, phenotypically antibiotic tolerant, bacteria are more resistant to antibiotics and may be responsible for relapse and the need for long-term TB treatment. We present a microfluidic system that acoustically traps live mycobacteria, M. smegmatis, a model organism for M. tuberculosis. We then perform optical analysis in the form of wavelength modulated Raman spectroscopy (WMRS) on the trapped M. smegmatis for up to eight hours, and also in the presence of isoniazid (INH). The Raman fingerprints of M. smegmatis exposed to INH change substantially in comparison to the unstressed condition. Our work provides a real-time assessment of the impact of INH on the increase of lipids in these mycobacteria, which could render the cells more tolerant to antibiotics. This microfluidic platform may be used to study any microorganism and to dynamically monitor its response to different conditions and stimuli.

The Isoniazid Paradigm of Killing, Resistance, and Persistence in Mycobacterium tuberculosis

Isoniazid (INH) was the first synthesized drug that mediated bactericidal killing of the bacterium Mycobacterium tuberculosis, a major clinical breakthrough. To this day, INH remains a cornerstone of modern tuberculosis (TB) chemotherapy. This review describes the serendipitous discovery of INH, its effectiveness on TB patients, and early studies to discover its mechanisms of bacteriocidal activity. Forty years after its introduction as a TB drug, the development of gene transfer in mycobacteria enabled the discovery of the genes encoding INH resistance, namely, the activator (katG) and the target (inhA) of INH. Further biochemical and x-ray crystallography studies on KatG and InhA proteins and mutants provided comprehensive understanding of INH mode of action and resistance mechanisms. Bacterial cultures can harbor subpopulations that are genetically or phenotypically resistant cells, the latter known as persisters. Treatment of exponentially growing cultures of M. tuberculosis with INH reproducibly kills 99% to 99.9% of cells in 3 days. Importantly, the surviving cells are slowly replicating or non-replicating cells expressing a unique stress response signature: these are the persisters. These persisters can be visualized using dual-reporter mycobacteriophages and their formation prevented using reducing compounds, such as N-acetylcysteine or vitamin C, that enhance M. tuberculosis' respiration. Altogether, this review portrays a detailed molecular analysis of INH killing and resistance mechanisms including persistence. The phenomenon of persistence is clearly the single greatest impediment to TB control, and research aimed at understanding persistence will provide new strategies to improve TB chemotherapy.

Levels of glycogen and trehalose in Mycobacterium smegmatis and the purification and properties of the glycogen synthetase

The levels of glycogen, free trehalose, and lipid-bound trehalose were compared in Mycobacterium smegmatis grown under various conditions of nitrogen limitation. In a mineral salts medium supplemented with yeast extract and containing fructose as the carbon source, the accumulation of glycogen increased dramatically as the NH(4)Cl content of the medium was lowered. However, levels of free trehalose remained relatively constant. Cells were grown in low nitrogen medium and were then shifted to medium containing high nitrogen. Under these conditions, there was a rapid accumulation of glycogen in low nitrogen, and this glycogen was rapidly depleted when cells were placed in high nitrogen medium. Again the concentration of free trehalose remained fairly constant. However, when cells were grown in low nitrogen medium with [(14)C]fructose and then transferred to high nitrogen medium with unlabeled fructose, the specific radioactivity (counts per minute per micromole) of the free trehalose fell immediately, indicating that it was being synthesized and turned over continually. On the other hand, the specific radioactivity of the glycogen and bound trehalose declined much more slowly, suggesting that these two compounds were not turning over as rapidly or were being synthesized at a much slower rate. Experiments on the incorporation of [(14)C]fructose into glycogen and trehalose indicated that cells in high nitrogen medium synthesized much less glycogen than those in low nitrogen. However, synthesis of both free trehalose and bound trehalose was the same in both cases. The specific enzymatic activities of the glycogen synthetase and the trehalose phosphate synthetase varied somewhat from one growth condition to another, but there was no correlation between enzymatic activity and the amount of glycogen or trehalose, suggesting that changes in glycogen levels were not due to increased synthetic capacity. The glycogen synthetase was purified about 35-fold and its properties were examined. This enzyme was specific for adenosine diphosphate glucose as the glucosyl donor.

The effects of isoniazid on the carbohydrates of Mycobacterium tuberculosis BCG

1. Mycobacterium tuberculosis BCG was usually grown in glycerol-asparagine-casein hydrolysate medium. A soluble fraction was obtained from the cells with aq. 50% ethanol; unbound lipids were then removed and the cells were treated with dilute alkali to give, after acidification, an alkali-extractable fraction and an insoluble fraction. On occasion, lipopolysaccharides were obtained by extracting with phenol or dimethyl sulphoxide instead of alkali. The soluble fraction contained, particularly after long extraction, polysaccharide containing mainly glucose, in addition to trehalose and monosaccharides and their derivatives. The alkali-extractable fraction contained polysaccharides containing mannose, glucose, arabinose, galactose and 6-O-methylglucose. These could be resolved into three fractions of markedly different molecular size. It is argued that the high-molecular-weight materials originated from the outside of the cell envelope and the medium-molecular-weight materials from a middle layer of the envelope. 2. Exposure of the growing cells to isoniazid, usually at 1 or 10mug/ml for 6-12h, increased the total cell carbohydrate, mainly due to an increase in trehalose and in insoluble glucan. It also facilitated the extraction of polysaccharide into the medium and the soluble fraction. This produced about a 25% decrease in the amount of carbohydrate in the alkaline-extractable fraction, mainly due to a fall in glucose, arabinose and 6-O-methylglucose. The decrease was confined to polysaccharides of large and medium molecular weight. When intact lipopolysaccharides were extracted, their amount was also decreased by isoniazid. 3. Substitution of ammonium sulphate for asparagine and casein hydrolysate in the medium, so that glycerol was the sole carbon source, decreased the carbohydrate accumulation brought about by isoniazid but did not alter its effect on polysaccharide extraction. 4. Growth with (14)C-labelled substrates showed that glycerol provided two to four times as much of the cell carbon as did asparagine, when both were present. Under these conditions isoniazid inhibited the incorporation of carbon atoms from asparagine into the cells, but had little effect on the total incorporation from glycerol. These experiments also showed that the effect of isoniazid on alkali-extractable polysaccharides was due to their loss to the soluble fraction and external medium. 5. It is suggested that isoniazid inhibits a pathway (probably the synthesis of mycolic acid) involved in the formation of the cell envelope, and that this inhibition results in some re-channelling of intermediates into carbohydrate synthesis and in some loss of polysaccharides through damage to the envelope.