Sublethal injury and recovery of Listeria monocytogenes and Escherichia coli O157:H7 after exposure to slightly acidic electrolyzed water

Abstract

Foodborne pathogens can survive as the state of sublethal injury in adverse environments and recover physiological function and virulence under suitable conditions. Slightly acidic electrolyzed water (SAEW) is a non-thermal treatment to decontaminate in food industry and can induce sublethal injury. However, sublethal injury induced by SAEW and recoveries of different pathogens have not been fully investigated. In this study, it was observed that sublethally injured L. monocytogenes and E. coli O157:H7 cells widely persisted after exposure to different SAEW treatments (both of two pathogens: volumes of SAEW 1–10 ml, concentrations of SAEW 25%–100%; L. monocytogenes: treatment time 30–180 s, E. coli O157:H7: treatment time 15–90 s). And the highest recovery ratio of injured L. monocytogenes or E. coli O157:H7 was observed in TSB-YE or TSB and these cells were completely recovered within 60 min or 2.5 h, respectively. The recovery ratio of SAEW-injured L. monocytogenes and E. coli O157:H7 increased as recovery temperature increasing (4–37 °C). Mg, Ca and Zn cations significantly improved the recovery ratios of both two pathogens, but Fe and Mn cations had negative effects on recovery. Moreover, the concentrations of cations (0.5–8 mM) affected repair. The most appropriate concentration of Mg, Ca or Zn cations improving the repair of injured L. monocytogenes was 1 mM, 8 mM or 0.5 mM, respectively. The recovery ratio of injured E. coli O157:H7 increased with the concentrations of Mg, Ca and Zn cations increasing. The understanding of SAEW-injured and resuscitated conditions of L. monocytogenes and E. coli O157:H7 can avoid the occurrence of injured cells in food processing and develop a medium for detecting injured pathogens.