Proposed mechanism of inactivatingEscherichia coliO157:H7 by ultra-high pressure in combination withtert-butylhydroquinone

Abstract

Aims: Investigating mechanisms of lethality enhancement when Escherichia coli O157:H7, and selected E. coli mutants, were exposed to tert‐butylhydroquinone (TBHQ) during ultra‐high pressure (UHP) treatment. Methods and Results: Escherichia coli O157:H7 EDL‐933, and 14 E. coli K12 strains with mutations in selected genes, were treated with dimethyl sulfoxide solution of TBHQ (15–30 ppm), and processed with UHP (400 MPa, 23 ± 2°C for 5 min). Treatment of wild‐type E. coli strains with UHP alone inactivated 2·4–3·7 log CFU ml−1, whereas presence of TBHQ increased UHP lethality by 1·1–6·2 log CFU ml−1; TBHQ without pressure was minimally lethal (0–0·6 log reduction). Response of E. coli K12 mutants to these treatments suggests that iron–sulfur cluster‐containing proteins ([Fe–S]‐proteins), particularly those related to the sulfur mobilization (SUF system), nitrate metabolism, and intracellular redox potential, are critical to the UHP–TBHQ synergy against E. coli. Mutations in genes maintaining redox homeostasis and anaerobic metabolism were associated with UHP–TBHQ resistance. Conclusions: The redox cycling activity of cellular [Fe–S]‐proteins may oxidize TBHQ, potentially leading to the generation of bactericidal reactive oxygen species. Significance and Impact of the Study: A mechanism is proposed for the enhanced lethality of UHP by TBHQ against E. coli O157:H7. The results may benefit food processors using UHP–based preservation, and biologists interested in piezophilic micro‐organisms.

Inactivation of Bacterial Spores by High Pressure and Food Additive Combination

“…It was also reported in earlier studies that some essential oils, which contain phenolic compounds, prevented the germination of C. botulinum spores [3,12,22]. Otherwise, it may suggest that TBHQ exerts its antioxidant property in anaerobes such as C. sporogenes, due to the alteration of cell metabolic pathways governing redox homeostasis [18]. It needs further investigation for the exact mechanism.…”

“…Combining HP and phenolics is a promising strategy to improve the safety of minimally-or nonthermally-processed foods. The enhanced antimicrobial activity of HP by tert-butylhydroquinone (TBHQ) was reported against food borne pathogens such as Listeria monoytogenes and Escherichia coli O157:H7 [5,18,29]. The cell membrane is suggested to be one of the targets for HP [4].…”

“…Therefore, physical damage to the cell membrane may be enhanced by phenolic ingredients during the pressure treatment. In addition, considering the antioxidant properties of TBHQ, presence of this compound during pressure treatment may have altered the cell metabolic pathways governing redox homeostasis [5,18,29]. However, studies depicting this synergy against bacterial spores are lacking.…”