In 1917, a group of German soldiers arrived at a military hospital near Freiburg after returning from a campaign in Dobrudja, a region of the Balkans that had been riddled with disease. All of the troops had been struck down with a nasty case of dysentery caused by the Shigella group of bacteria – except for one soldier, who was remarkably unaffected by the deadly illness that struck down his comrades.

The case caught the attention of Professor Alfred Nissle, a physician at the hospital who had grown increasingly interested in the bacterial contents of the human intestine.