The B. subtilis, E. coli, S. marcescens, M. flavescens, and C. lypolitica were cultured either on medium
M9 added with 1 % glucose or on the FMH for two hours. an average microbial density of the lawn produced
on Petri dishes was 2.4–7.5 × 106 cells/cm2.
The A. niger, the spore-forming culture, was grown on Czapek medium at 37 °C over 7 days.
Produced spores were suspended with a saline solution. Suspension of 100 μL in volume was evenly
spread over the surface of freshly prepared Czapek agar. The average spore density was 106 spores/cm2.
In the case of surface sterilization, the jet of plasma was directed perpendicularly to the middle
of a Petri dish located at the distance of 1 cm away from a plasma nozzle. The plasma treated dishes
were incubated overnight at 37 °C in an incubator (for 3 days in the case of fungi). Diameters of the inactivated
zones were measured.
Plasma sterilization efficiency of the spore-contaminated surfaces was characterized with use of
the standard B. subtilis spore-immobilized test strips (about 106 spores per each strip). The strips to be
treated were stood edgewise toward the jet. After the treatment, each strip was aseptically transferred
to an individual tube containing the test medium with added tryptone and phenol red dye. The tubes
were incubated at 37 °C in an incubator. The effect of plasma sterilization was judged from the changes
in the medium color in 7 days of the incubation. The absence of changes in color (still red) meant that
the sample was sterile, while a change in color from red to yellow indicated the presence of the living
microorganisms in the sample.