3M's Attest 1261 Biological Indicator (blue cap) is designed for monitoring 270° F (132° C) gravity displacement steam sterilization processes. The presence of active Geobacillus stearothermophilus spores is detected by a visual color change (media turns yellow). The yellow color change indicates a sterilization process failure. The final readout of a negative result (media remains purple) is made after 24 hours of incubation. - Blue cap. Self-contained indicators significantly reduce possibility of contamination, minimizing false positive and assuring more accurate results..