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Scientists who unlocked the genetic code of bacteria grown from a soldier who died of dysentery in World War I say it revealed a superbug already resistant to penicillin and other antibiotics decades before they were in common use.

The discovery sheds light on the history of antibiotic resistance - now a global health threat.

It also offers fresh clues on how to tackle dysentery, a disease that kills hundreds of thousands of children every year in developing countries. 

Trench warfare on the Marne German gun position: Researchers say superbugs already resistant to penicillin and other antibiotics decades beforethey were in common use were rife

'Even before the description and widespread use of penicillin, this bacterium was resistant to it,' said Kate Baker of Britain's Wellcome Trust Sanger Institute, who worked on the research with colleagues at Public Health England (PHE).

Researchers focused on a bacterial sample retrieved from the British soldier - Private Ernest Cable of the East Surrey Regiment - who died in March of 1915

Dysentery is a life-threatening disease that is becoming increasingly hard to treat due to its growing ability to evade antibiotic treatment. 

It was rife in the trenches during World War I, and still spreads now in unsanitary conditions in poor countries and in conflict zones.

The genetic data from this sample of bacteria. known as Shigella flexneri.which infected a soldier on the Western Front, show how the pathogen has changed in the past century.

Baker's research is to be published in The Lancet medical journal on Saturday.

She said in a telephone interview that analysis of genetic differences between this 1915 sample of Shigella flexneri and three others isolated in 1954, 1984 and 2002 showed that while the bacterium has changed relatively little, the mutations it has acquired have made it more dangerous and persistent.

The discovery sheds light on the history of antibioticresistance - now a global health threat.

It also went though what is known as a 'serotype conversion', she said, which made it able to re-infect and cause illness in people who had already been infected before and would previously have been immune to further attacks.

The three other samples were one known as 2457T from a Japanese patient in 1954, a strain called 301 taken from Beijing in 1984, and a further epidemic strain from China from 2002.

'Only 2 percent of its (Shigella's) genome differed over that time,' Baker said. 

'But the changes is has acquired were crucial to helping it evade the antimicrobials (antibiotics) we use to fight it. It's quite remarkable.'

She said she hoped the findings may ultimately help her team and other scientists in the search for an effective vaccine for Shigella, since there are now few existing antibiotics to which the bug has not developed some level of resistance.