Scientists in New Zealand and the Netherlands have made a breakthrough in understanding a bacterial immune system that might help in stopping antibiotic- resistant genes.

The researchers were investigating an adaptive immune system, called CRISPR-Cas, which is found in half of all bacterial species and in almost all single-celled microbes in the archaea domain of bacteria, said research leader Dr Peter Fineran of New Zealand's Otago University.

The CRISPR-Cas system stole samples of a virus or plasmid invader's genetic material and stored them in a memory bank so it could immediately recognize future exposures and neutralize the attack.

It could store up to 600 samples and also pass the memories on to subsequent generations of bacteria.

It had been thought that the system had a weakness because invaders that had acquired too many mutations could no longer be recognized in the memory bank.

"What we have now discovered is that while the viruses and plasmids can evade direct recognition by acquiring multiple mutations, the system is primed to quickly generate a new immunity by grabbing a new sample of the mutated genetic material," Fineran said in a statement Tuesday.

The system reflected the ancient and continuing co-evolutionary arms race between bacteria on one side, and viruses and plasmids on the other, he said.

"Their silent, but vast and ongoing war underpins everything from how global nutrient cycles, which rely on bacteria to produce half of the Earth's biomass, operate, to how human pathogens evolve," he said.

"For example, the bacteria that cause cholera and diphtheria have been infected by viruses that provide genes coding for toxins, which converted these bacteria into significant human pathogens."

Plasmids were key players in moving antibiotic resistance genes between different bacterial species, he said.