Oranges: a cure for drug-resistant TB?

Scientists at the Albert Einstein College of Medicine of Yeshiva University have observed the bactericidal effects of vitamin C against tuberculosis – crucially, this does not cause development of resistance. This finding could lead to novel treatments against tuberculosis, including multi-drug resistant (MDR) and extensively drug-resistant (XDR) bacteria.

Tuberculosis is caused by the mycobacterium tuberculosis, which typically infects the lungs. Whilst the death rate has dropped 41% between 1990 and 2011 due to antibiotics, there were still 1.4 million deaths in 2011. Antibiotic resistance is also becoming an increasingly common problem, and the long duration of chemotherapy for resistant strains comes with damaging side effects.

The team, led by William Jacobs, used M.tuberculosis cultures to show the sterilising effect of vitamin C in vitro. It was seen that there was a dose-dependent response, with bacteriostatic effects seen at 1mM, and bactericidal effects at 2mM. In addition, these effects were seen to be synergistic with isoniazid (a first line drug). With both MDR and XDR strains, a 100,000-fold reduction in colony forming units was observed after 2 weeks of vitamin C treatment.

The lab provided evidence supporting the theory that vitamin C acts as a pro-oxidant to drive the Fenton reaction, a reaction that leads to the production of free radicals that could damage bacterial DNA. Furthermore, it is thought that it disrupts lipid biosynthesis and redox homeostasis in the bacterium. This combinatorial effect could explain why vitamin C is able to kill XDR-TB, and why no vitamin C resistant bacteria were obtained during the experiments. Further study must be undertaken to see whether high vitamin C diet in combination with current therapy could reduce both treatment duration and mutation rates.