Put the blackberries, strawberries and blueberries in a blender with 1.4 fl oz of water and blend.
Heat a saucepan and add the berry mixture with sugar and vinegar.
Allow to reduce for ten minutes and set aside.
Place the tenderloin on the grill over medium heat, add salt to taste and flip every 5 minutes to cook evenly.
After about 20 minutes, remove the tenderloin and cut it into about 1-inch medallions.
Wrap each piece in bacon (you can use cocktail picks to hold it steady).
Finish cooking the medallion on the grill 1 minute per side.