Effect of gamma radiation and oregano essential oil on murein and ATP concentration of Escherichia coli O157:H7
2005
Caillet, S. | Shareck, F. | Lacroix, M.
This study was carried out to evaluate the effects of gamma radiation alone or in combination with oregano essential oil on the murein composition of Escherichia coli O157:H7 and on the intracellular and extracellular concentrations of ATP. The bacterial strain was treated with three radiation doses: 0.4 kGy to induce cell damage, 1.1 kGy to obtain a viable but nonculturable state, and 1.3 kGy to cause cell death. Oregano essential oil was used at 0.006 and 0.025% (wt/vol), which is the MIC. All treatments had a significant effect (P less than or equal to 0.05) on the murein composition, although some muropeptides did not seem to be affected by the treatment. Each treatment had a different effect on the relative percentage and number of muropeptides. There was a significant correlation (P less than or equal to 0.05) between the decrease in intracellular ATP and the increase in extracellular ATP following treatment of the cells with oregano oil. The reduction of intracellular ATP was even more important when oregano oil was combined with irradiation, but irradiation alone at a high dose (less than or equal to 1.1 kGy) significantly decreased (P less than or equal to 0.05) the internal ATP without affecting the external ATP. Transmission electron microscopic examination revealed that oregano oil and irradiation have an effect on cell wall structure.
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