Vitamin C has been found to kill drug-resistant forms of tuberculosis, meaning existing drugs can be redesigned to combat the disease.

Researchers at the Albert Einstein College of Medicine, part of Yeshiva University in New York, have found that vitamin C kills drug-resistant TB in laboratory culture.

TB is a common and often lethal disease that attacks the lungs. It spreads through the air when people have an active TB infection.

Drug-resistant TB is now a major public health concern caused by the improper use of antibiotics. There are around 440,000 new cases of drug-resistant TB diagnosed every year which result in 150,000 deaths. In total, around 650,000 people worldwide now have drug-resistant TB.

The discovery of vitamin C's effect on drug-resistant TB was "unexpected", the scientists said.

Published in the online journal Nature Communications, the researchers were looking at how TB becomes resistant to isoniazid, a first line TB drug.

William Jacobs, lead investigator of the study, found that isoniazid-resistant TB was deficient in a molecule called mycothiol - suggesting TB cannot make this molecule and may contain more of an amino acid called cysteine.

Drug resistant tuberculosis
Around 650,000 people worldwide now have drug-resistant TB (Reuters)

"We predicted that if we added isoniazid and cysteine to isoniazid-sensitive M. tuberculosis in culture, the bacteria would develop resistance. Instead, we ended up killing off the culture- something totally unexpected."

The team then suggested that cysteine was helping to kill the drug-resistant TB by triggering the production of reactive oxygen species, a by-product of the metabolism of oxygen that damages DNA.

To test the theory, they repeated the experiment using isoniazid and Vitamin C, which also acts as a reducing agent.

"The combination of isoniazid and vitamin C sterilized the M. tuberculosis culture. We were then amazed to discover that vitamin C by itself not only sterilized the drug-susceptible TB, but also sterilized multi-drug-resistant tuberculosis and extensively drug-resistant tuberculosis strains," Jacobs said.

After further research, the team found vitamin C kills the virus by inducing what is known as a Fenton reaction. This causes iron to react with other molecules to create reactive oxygen species, which in turn kills the TB bacteria.

"We don't know whether vitamin C will work in humans, but we now have a rational basis for doing a clinical trial," said Dr. Jacobs.

"It also helps that we know vitamin C is inexpensive, widely available and very safe to use. At the very least, this work shows us a new mechanism that we can exploit to attack TB."