2.4. Microbiological Analysis

For the enumeration of E. coli Endo medium was used (BTL Ltd., Łódź, Poland). The decimal solutions (from 10⁻¹ to 10⁻⁷) were made by using the Ringer’s solution and a vortex shaker was used to mix the solutions (Vortex Classic, Velp Scientifica, Usmate Velate MB, Italy). The E. coli enumeration was performed by adding 0.1 mL of the decimal solution sample to the Petri dishes with Endo medium. After that, the Petri dishes were incubated at 37 ± 1 °C for 24 ± 2 h. After incubation time, the circular, black and metallic shine colonies of E. coli were counted. Each experiment was performed in three repetitions. The mean value of the obtained results was expressed as log₁₀CFU in 1 gram of the sample and calculated according to Equation (4).

where: a is the number of colonies of E. coli, b is the volume of plated sample and x is the dilution coefficient.

The analysis was conducted in the same way for treated (CaO₂) and untreated samples.