Plasma effects on the bacteria Escherichia coli via two evaluation methods

Abstract

The degradation of Escherichia coli bacteria by treatment with cold, weakly ionised, highly dissociated oxygen plasma, with an electron temperature of 3 eV, a plasma density of 8 × 1015 m−3 and a neutral oxygen atom density of 3.5 × 1021 m−3 was studied. To determine the ‘real’ plasma effects, two methods were used for evaluation and determination, as well as a comparison of the number of bacteria that had survived: the standard plate count technique (PCT) and advanced fluorescence-activated cell sorting (FACS). Bacteria were deposited onto glass substrates and kept below 50 °C during the experiments with oxygen plasma. The results showed that the bacteria had fully degraded after about 2 min of plasma treatment, depending slightly on the amount of bacteria that had been deposited on the substrates. The very precise determination of the O flux on the substrates and the two-method comparison allowed for the determination of the critical dose of oxygen atoms required for the destruction of a bacterial cell wall—about 6 × 1024 m−2—as well as deactivation of the substrates—about 8 × 1025 m−2. These results were taken in order to discuss other results obtained by comparable studies and scientific method evaluations in the determination of plasma effects on bacteria.