Scientists have reported the discovery of a key "survival gene" which prevents strains of tuberculosis (TB) from mutating into drug resistant "superbugs".

The gene, called NucS, has been found to "dramatically" reduce mutation rates in mycobacteria - the infectious microbe which causes TB.

Scientists from the University of Sussex in Brighton and the Centro Nacional de Biotecnologia in Madrid say the discovery could play a role in understanding the development of antibiotic resistance in patients already suffering from TB.

TB, which is spread from person to person through the air, is one of the top 10 causes of death worldwide with 1.8 million people dying from the disease last year.

Drug resistant strains of TB have already been identified in 105 countries and the researchers involved in this study believe that identification of the key gene, required to suppress mutation rates in mycobacteria, is an important step towards understanding how superbugs develop.

The rise of antibiotic resistance is a major threat to global health

Aidan Doherty, from the University of Sussex, said: "The rise of antibiotic resistance is a major threat to global health and, if we are to limit its impact on infectious diseases, we first need to identify the mechanisms that prevent bacteria from mutating in the first place."

"This knowledge will then enable us to better understand how pathogens develop into 'superbugs'.

"Incredibly, for many years it was believed that mycobacteria lacked any mutation avoidance genes.

"Therefore, the discovery that the NucS gene reduces the rate at which mutations occur in these pathogens is a crucial first step towards identifying the genetic factors that influence the onset of antibiotic resistance."

"This will enable scientists and clinicians to screen for strains that are most likely to develop drug resistance and figure out strategies to tackle this serious threat."

Using a genetic screen, which involved individually knocking out nearly every gene (11,000) in mycobacteria, and screening whether mutant strains grew on a specific antibiotic (rifampicin), the scientists discovered that a DNA repair enzyme, produced by the NucS gene, dramatically reduced mutations from occurring.

The researchers also discovered that genetic variations in the NucS gene significantly influenced the mutation rates in clinically isolated strains of mycobacteria.

Not only does this study identify that mutations can be reversed in mycobacteria, it reveals that the loss of this DNA repair process can cause a huge increase in the mutation rates

Jesus Blazquez, from the Centro Nacional de Biotecnologia, said: "Not only does this study identify that mutations can be reversed in mycobacteria, it reveals that the loss of this DNA repair process can cause a huge increase in the mutation rates, significantly increasing the likelihood of these pathogens acquiring mutations - which can cause antibiotic resistance.

"Now we know that NucS dramatically reduces mutation rates in mycobacteria, it is vital that we take advantage of this and work towards exploiting this discovery to help doctors and microbiologists to predict and prevent the development of antibiotic resistance during treatments."