title: Mechanisms of Inactivation of Dry Escherichia coli by High-Pressure Carbon Dioxide.
abstract: High-pressure carbon dioxide processing is a promising technology for nonthermal food preservation. However, few studies have determined the lethality of high-pressure CO2on dry bacterial cells, and the mechanism of inactivation remains unknown. This study explored the mechanisms of inactivation by usingEscherichia coliAW1.7 and mutant strains differing in heat and acid resistance, in membrane composition based on disruption of the locus of heat resistance, and in genes coding for glutamate decarboxylases and cyclopropane fatty acid synthase. The levels of lethality of treatments with liquid, gaseous, and supercritical CO2were compared. The cell counts ofE. coliAW1.7 and mutants with a water activity (aW) of 1.0 were reduced by more than 3 log10(CFU/ml) after supercritical CO2treatment at 35°C for 15 min; increasing the pressure generally enhanced inactivation, except forE. coliAW1.7 ΔgadABE. coliAW1.7 Δcfawas more susceptible thanE. coliAW1.7 after treatment at 10 and 40 MPa; other mutations did not affect survival. Dry cells ofE. coliwere resistant to treatments with supercritical and liquid CO2at any temperature. Treatments with gaseous CO2at 65°C were more bactericidal than those with supercritical CO2or treatments at 65°C only. Remarkably,E. coliAW1.7 was more susceptible thanE. coliAW1.7 Δcfawhen subjected to the gaseous CO2treatment. This study identified CO2-induced membrane fluidization and permeabilization as causes of supercritical mediated microbial inactivation, and diffusivity was a dominant factor for gaseous CO2IMPORTANCEThe safety of dry foods is of increasing concern for public health. Desiccated microorganisms, including pathogens, remain viable over long periods of storage and generally tolerate environmental insults that are lethal to the same organisms at high water activity. This study explored the use of high-pressure carbon dioxide to determine its lethality for driedEscherichia coliand to provide insight into the mechanisms of inactivation. The lethality of high-pressure CO2and the mechanisms of CO2-mediated inactivation of dryE. colidepended on the physical state of CO2Liquid and supercritical CO2were ineffective in reducing the cell counts of dryE. coliisolates, and the effectiveness of gaseous CO2was related to the diffusivity of CO2Results provide a novel and alternative method for the food industry to enhance the safety of low aWproducts.
authors.affiliation: University of Alberta, Department of Agricultural, Food, and Nutritional Science, Edmonton, Alberta, Canada.
authors.forename: Yuan Yao
authors.initials: YY
authors.lastname: Chen
authors.affiliation: University of Alberta, Department of Agricultural, Food, and Nutritional Science, Edmonton, Alberta, Canada.
authors.forename: Feral
authors.initials: F
authors.lastname: Temelli
authors.affiliation: University of Alberta, Department of Agricultural, Food, and Nutritional Science, Edmonton, Alberta, Canada mgaenzle@ualberta.ca.
authors.forename: Michael G
authors.identifier: http://orcid.org/0000-0003-0972-928X
authors.initials: MG
authors.lastname: Gänzle
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005519:Food Preservation / Q000295:instrumentation / Q000379:methods*; D006358:Hot Temperature; D050296:Microbial Viability; D009154:Mutation; D011312:Pressure; D013696:Temperature; D014867:Water / Q000032:analysis / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D014867:Water; D002245:Carbon Dioxide
keywords: CO2 diffusivity; cyclopropane fatty acid synthase; gaseous CO2; membrane fluidity and permeability; supercritical CO2; water activity