Botulism can be killed with exposure to heat 250 degrees or higher. If heat doesn't quite get to 250 degrees then prolonged exposure must happen to kill botulism. In the case of pressure cookers operating at full 15 PSI at sea level the temperature inside can reach 250 degrees before water turns to steam.

How long until pressure kills botulism?

University of Wyoming says, “Regardless of the age of the food, always boil low-acid, pressure-canned food a full 10 minutes plus one minute per 1,000 feet [300 metres] of altitude above sea level to destroy any botulism toxins.

Can botulism survive pressure canning?

Botulism spores are tough, and cannot be killed with boiling water or heat without including canning pressures.