title: Inactivation of Staphylococcus aureus and Escherichia coli by the synergistic action of high hydrostatic pressure and dissolved CO₂.
abstract: This study focused on the synergistic inactivation effects of combined treatment of HHP and dissolved CO₂ on microorganisms. The aim was to reduce the treatment pressure of the traditional HHP technology and make it more economically feasible. The combined treatment showed a strong bactericidal effect on Staphylococcus aureus and Escherichia coli in liquid culture, which usually have high levels of barotolerance under pressure alone. To identify the influence of CO₂, a new setup to dissolve, retain and measure the concentration of CO₂ was constructed. The results demonstrated that an inactivation rate of more than 8 log units was obtained for E. coli both at 300 MPa with 1.2 NL/L CO₂ and at 250 MPa with 3.2 NL/L CO₂, while only 2.2 and 1.8 log reductions were observed at 300 MPa and 250 MPa, respectively, for the HHP treatments alone. For S. aureus, the inactivation rate of more than 7 log units was found at 350 MPa with 3.8 NL/L CO₂, while only a 0.9 log reduction was achieved at this pressure in the absence of CO₂. The SEM photographs showed seriously deformed cells after the synergistic treatments. In contrast, the cells treated with individual HHP maintained a relatively smooth surface with invaginations. Propidium iodide staining and fluorescence observation was performed after pressure treatments. The results demonstrated that the combination of CO₂ with HHP also promoted pressure induced cell membrane permeabilization greatly. It was deduced that the enrichment of CO₂ on the cell surface and its penetration into the cells at high pressure accounted for the membrane damage and cell death.
authors.affiliation: Engineering Research Centre of Bio-Process, Ministry of Education of China, Hefei University of Technology, Hefei, Anhui 230009, PR China.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Jian
authors.initials: J
authors.lastname: Pan
authors.forename: Huiming
authors.initials: H
authors.lastname: Xie
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Chunming
authors.initials: C
authors.lastname: Lin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D005511:Food Handling / Q000379:methods; D006874:Hydrostatic Pressure; D050296:Microbial Viability / Q000187:drug effects*; D008855:Microscopy, Electron, Scanning; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D013242:Sterilization / Q000379:methods*
chemical_list: D000900:Anti-Bacterial Agents; D002245:Carbon Dioxide