A 32-year-old female surgical nurse presents to occupational health with a history of recurrent needle-stick injuries over the past 6 months. The hospital's infection control committee is reviewing sterilization protocols for reusable surgical instruments in the operating theatre. During an audit, they discover that several instrument trays are being processed through a steam autoclave at 121°C for only 10 minutes at 15 psi, despite manufacturer recommendations of 15–20 minutes. Three weeks later, a post-operative patient develops a surgical site infection with Mycobacterium tuberculosis. Which sterilization parameter was most likely compromised, leading to survival of this pathogen?