Proteus OX19 is a strain of the Proteus vulgaris bacterium.
Drs. Eugeniusz Lazowski and Stanisław Matulewicz worked with Proteus OX19 during World War II in the small town of Rozwadów in Poland to keep Nazi Germany from taking over the town. The doctors began inoculating villagers with dead Proteus, rendering false positives in tests for typhus. When the blood samples of the townspeople were sent to the German authorities for testing, authorities were convinced a typhus epidemic was burning through Rozwadów. The two Polish doctors used Proteus OX19 to save thousands of Poles and Jews.