Vitamin C Kills Mycobacterium tuberculosis

Ricki Lewis, PhD

May 22, 2013

Vitamin C kills drug-sensitive, multidrug-resistant (MDR), and extensively-drug resistant (XDR) strains of Mycobacterium tuberculosis in culture as a result of prooxidant effects, according to a report published online May 21 in Nature Communications.

The new work builds on the long-standing observation that vitamin C is toxic to M tuberculosis, a Gram-positive bacterium. Experiments in the 1930s showed that only 6% of guinea pigs exposed to the bacteria and given tomato juice became infected compared with 70% of guinea pigs not given the vitamin C–rich juice. In vitro experiments conducted in 1950 confirmed the effect of the vitamin on bacterial cultures, and a study in 2011 correlated vitamin C content of various medicinal plants with antibacterial effects.

In the current study, Catherine Vilcheze, PhD, from the Department of Microbiology and Immunology, Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, New York, and colleagues conducted dose–response experiments, determining that 2 mM is the bactericidal level for drug-sensitive, MDR, and XDR bacteria. The effect was not seen when the bacteria were cultured in an anaerobic chamber. M tuberculosis is much more sensitive to the prooxidant effects of the vitamin than other Gram-positive and Gram-negative bacteria.

Analysis of transcription patterns revealed that the vitamin-exposed cells accumulated ferrous ions, which is consistent with the known bactericidal mechanism of vitamin C. The vitamin reduces ferric to ferrous iron, and the ferrous ions react with oxygen to produce hydroxyl radicals, which are a type of reactive oxygen species. The hydroxyl radicals damage guanine residues in DNA, causing cell death.

On the basis of these data, the researchers suggest that adding vitamin C to treatment regimens might shorten the time that chemotherapy is necessary, which is currently from 6 to 24 months. Noncompliance with chemotherapy fuels selection of drug-resistant bacterial strains. The findings also suggest that drug developers might look for the prooxidant effects of drug candidates.

"The dramatic killing of drug-susceptible, MDR and XDR M. tuberculosis strains by [vitamin C] in vitro argues for further studies on the benefits of a high [vitamin C] diet in TB-treated patients and on the development of bactericidal drugs based on [reactive oxygen species] production," the researchers conclude.

The authors have disclosed no relevant financial relationships.

Nat Comm. Published online May 21, 2013. Abstract

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