Methods: The sporulation efficiency of Geobacillus stearothermophilus was tested in 4 different kinds of media with varying concentrations of manganese sulfate. Biological indicators were produced by spotting approximately 5 x 105 bacterial spores on sterile paper strip carriers according to the International Standardization Organization 11138-1:2006 and 11138-3:2006. The efficiency of the indicators was examined in both optimal (121ºC, 20 min) and sub-optimal (110ºC, 20 min) conditions in an autoclave. Three batches of 50 biological indicators each were tested in comparison to 50 commercial indicators (RavenTM) in each condition. Autoclaved indicators were incubated in TSB medium with bromcresol purple at 60ºC and results were read after 1, 2, 3, and 7 days of incubation.
Results: Nutrient broth with the addition of manganese sulfate at 15 ppm was the most efficient sporulation inducing medium. The sensitivity of the in-house biological indicators was 99.3% (95% confidence interval (CI)=96.3-99.9%) and specificity was 94.7% (95% CI=89.8-97.3%). In comparison, the commercial indicators had a sensitivity of 98% (95% CI=89.5-99.7%) and a specificity of 100% (95% CI=92.9-100%).
Conclusions: In-house biological indicators produced from spores of Geobacillus stearothermophilus grown in nutrient broth supplemented with 15 ppm manganese sulfate have comparable sensitivity and specificity to a commercially available indicator.