Alteration in Escherichia coli and Streptococcus faecalis cells induced by ozone

To elucidate ozone action mechanism, cell suspensions of E. coli 8099 and S. faecalis ATCC29212 were initially exposed to ozone for 5 min, and then treated with sodium dodecyl sulfate, sodium hydroxide, and proteinase K. those of S. faecalis were 7.95±2.81%–55.85±1.43%. After ozone pre-treatment, OD600 value of E. coli cells, sequently treated with SDS, NaOH, and PK, decreased by 8.83±1.86%, 34.72±0.42%, and 10.42±2.08%, respectively. And that of S. feacalis decreased by 2.85±3.63%, 71.30±1.08%, and 7.00±2.47%, respectively. Therefore, ozone pre-treatment made E. coli cells be sensitive to SDS and NaOH, not susceptible to PK. It was confirmed by transmission electron microscopy of E. coli cells. To S. faecalis, ozone pre-treatment activated the effects of SDS, NaOH, and PK on cells. ATP loss from S. faecalis cells indicated that ozone damaged cell membrane and increased membrane permeability. Because SDS-, NaOH-, and PK-induced cell lyses were respectively due to protein denaturation, cell membrane damage, and the reactions between PK and proteins or conjugated proteins, it was concluded that protein changes and cell membrane damage generated by ozone are responsible for E. coli and S. faecalis inactivation. Results showed that, after ozone treatment, OD600 reduction rates of E. coli cells were 6.11±1.29%–7.06±1.23%.