Abstract: The combined antibacterial effect of γ irradiation and cinnamon essential oil (CEO) against Shewanella putrefaciens was evaluated and the underlying mechanism was investigated. The irradiation dose required to reduce total colony number to 10% of the initial level (D10) was reduced and the relative irradiation sensitivity was increased with increased concentration of CEO. The combination of γ irradiation and CEO was more effective in inhibiting the growth of S. putrefaciens than each alone. The combination treatment exhibited an obvious negative effect on cell morphology, intracellular ATP and pH, membrane proteins and fatty acids in S. putrefaciens. The combination resulted in a reduction of 40 kD subunits and an increase of 18 kD subunits in membrane proteins, as well as a significant reduction of C14:0, C16:0, C16:1, C17:1, and C18:1 in membrane lipids (P < 0.05). The mechanism for the synergism was due to the potential of γ irradiation to increase the destructive effect of CEO on the cell membrane of S. putrefaciens thus causing its death.

Key words: irradiation, cinnamon essential oil, Shewanella putrefaciens, synergistic effect, antimicrobial mechanism