I don't have "Under Pressure," but I have read of people working from the book cooking short ribs at 135F for 72 hrs. I have done that 4 - 5 times. No problems. Merely anecdotal.
MC published several charts, and made inferences about safe cooking below 140.
There was a US gov. site that offered an online charting program that would show how long it took for pathogens to reach hazardous levels at different temperatures.
The online source seems to be changing around, but you might want to look at:
If I understand what I've read (fingers crossed) , foods can be pasteurized below 140F, but the time to reach sterilization is extraordinarily long. If the foods are very contaminated, probably not worth the time and energy to sterilize.