Scientists have developed a simple method of converting blood from one group to another.

The breakthrough could potentially mean the end of blood shortages by boosting much-needed supplies of group O negative blood. That blood type is known as "universal" because it can be given to anyone. Giving patients the wrong blood type can result in death.

Writing in the journal Nature Biotechnology, an international team of researchers described how they converted blood from group A, B or AB to group O. The process uses bacterial enzymes as biological "scissors" to cut sugar molecules from the surface of red blood cells.

People in groups A and B have blood containing one of two different sugar molecules which can trigger an immune response. Those in group O have neither of these "antigens", while those in group AB have both.

The scientists, led by Professor Henrik Clausen, from the University of Copenhagen in Denmark, started by screening 2,500 types of fungi and bacteria looking for useful proteins.

Two bacteriums, Elizabethkingia meningosepticum, and Bacteroides fragilis, yielded enzymes capable of removing both A and B antigens from red blood cells.

That was verified by standard laboratory tests. After an hour's exposure to the appropriate enzyme, the antigens vanished from 200 millilitre samples of A, B and AB blood.

The researchers wrote: "Clinical translation of this approach may allow improvement of the blood supply and enhancement of patient safety in transfusion medicine."

Patient trials will have to take place before group O blood produced by the conversion method can be used in hospitals.