Escherichia coli inactivation mechanism by pressurized CO 2 (original) (raw)
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Inactivation of Escherichia coli by Carbon Dioxide under Pressure
Journal of Food Science, 1996
Thermal inactivation of Escherichia coli was studied under CO 2 pressures of 1.2, 2.5, and 5 MPa at 25, 35, and 45ЊC. Two phases were observed in the destruction curves. The earlier stage was characterized by a slow rate of inactivation, which increased sharply at the later stage. An increase of pressure and/or temperature enhanced the antimicrobial effects of CO 2 under pressure. The effects on cell structure were studied by scanning electron microscopy and the specific mechanism of action appeared to be related to enzyme inactivation.
Inactivation of Escherichia coli and bacteriophage T4 by high levels of dissolved CO2
Applied Microbiology and Biotechnology, 2011
Little information is available regarding the effectiveness of water disinfection by CO 2 at low pressure. The aim of this study was to evaluate the use of high levels of dissolved CO 2 at 0.3-0.6 MPa for the inactivation of microorganisms. Bacteriophage T4 was chosen as the model virus and Escherichia coli was selected as the representative bacterium. The results of the study showed a highly effective log inactivation of E. coli and bacteriophage T4 at low and medium initial concentrations by high levels of dissolved CO 2 at 0.3 MPa with a treatment time of 20 min. When the pressure was increased to 0.6 MPa, inactivation of both microorganisms at high initial concentrations was improved to different extents. Neither pressurized air nor O 2 effectively inactivated both E. coli and bacteriophage T4. The pH was not a key factor affecting the inactivation process by this method. The results of scanning electron microscopy of E. coli and transmission electron microscopy of bacteriophage T4 suggested that "CO 2 uptake at high pressure and bursting of cells by depressurization" were the main reasons for lethal effect on micro-organisms. This technology has potential for application in the disinfection of water, wastewater, and liquid food in the future.
Effect of compressed carbon dioxide on microbial cell viability
Applied and environmental microbiology, 1999
In order to study the influence of compressed carbon dioxide, over a range of pressures (1.5 to 5.5 MPa) and exposure times (up to 7 h), on the survival of Escherichia coli, Saccharomyces cerevisiae, and Enterococcus faecalis, a new pressurizable reactor system was conceived. Microbial cells were inoculated onto a solid hydrophilic medium and treated at room temperature; their sensitivities to inactivation varied greatly. The CO2 treatment had an enhanced efficiency in cell destruction when the pressure and the duration of exposure were increased. The effects of these parameters on the loss of viability was also studied by response-surface methodology. This study showed that a linear correlation exists between microbial inactivation and CO2 pressure and exposure time, and in it models were proposed which were adequate to predict the experimental values. The end point acidity was measured for all the samples in order to understand the mechanism of microbial inactivation. The pHs of t...
Effect of high pressurized carbon dioxide on Escherichia coli
Tanzania journal of science, 2009
Carbon dioxide at high pressure can retard microbial growth and sometimes kill microorganisms depending on values of applied pressure, temperature and exposure time. In this study the effect of high pressurised carbon dioxide (HPCD) on Escherichia coli was investigated. Culture of E. coli was subjected to high pressurised carbon dioxide at 15, 25 and 35 bar, and varying exposure times of 20, 40, 60 and 90 minutes at room temperature (27 o C). Microbial inactivation increased with pressure and exposure time. For the first 20 minutes reduction of viable microbial cells was 18%, 30% and 36% at 15, 25 and 35 bar, respectively. Higher microbial inactivation values were achieved at 40, 60, and 90 minutes. Decimal reduction times were 127, 93 and 75 minutes at 15, 25, and 35 bar, respectively. The pH values of treated samples decreased with increasing pressure and treatment time from approximately neutral to 5.71 at 15 bar, and 5.02 at 35 bar. It was concluded that high pressurised carbon dioxide has antimicrobial effect on E. coli bacteria. With further studies, HPCD microbial deactivation can be used for foods preservation as a alternative technology to conventional heat pasteurisation and sterilization.
Inactivation of Salmonella typhimurium by high pressure carbon dioxide
Food Microbiology, 2000
Thermal inactivation of Salmonella typhimurium was studied under CO 2 pressures of15, 30 and 60 atm at 25, 35 and 458C. Two phases were observed in the destruction curves. The earlier stage was characterized by a slow rate of inactivation in the number of S. typhimurium, which increased sharply at the later stage. It was suggested that the cell death resulted from the lowered pH due to solubilization of CO 2. An increase of pressure and/or temperature enhanced the antimicrobial e¡ects of CO 2. Salmonella typhimurium suspended in physiological saline (PS) was completely inactivated under 60 atm CO 2 treatment in 35 and 15 min at 25 and 358C, respectively. On the other hand, it was completely inactivated when suspended in PS containing brain^heart infusion broth for140 and100 min. A minimum Dvalue was obtained under 60 atm CO 2 pressure at 458C. Inactivation rates of S. typhimurium were sensitive to pressure, temperature, exposure time, initial number of cells, and the suspending medium.
Food Research International, 2014
The inactivation kinetics of Escherichia coli (E. coli) and Saccharomyces cerevisiae (S. cerevisiae) cells in apple juice subjected to supercritical carbon dioxide (SC-CO2) assisted by high power ultrasound (HPU) at different pressures (100-350 bar, 36 ºC) and temperatures (31-41 ºC, 225 bar) were studied. On average, shorter process times were required to achieve the total inactivation of S. cerevisiae (2-6 min) in apple juice than E. coli (7 min). The inactivation kinetics of E. coli and S. cerevisiae were satisfactorily described by the Peleg Type A and the Weibull model, respectively, considering temperature and pressure as model parameters. Transmission electron microscopy (TEM) and light microscopy (LM) techniques were used to study the cellular changes of SC-CO2 (350 bar, 36 ºC, 5 min) and SC-CO2+HPU (350 bar, 36 ºC, 5min, 40 W) treated cells. TEM and LM images revealed that 5 min of SC-CO2 treatment generated minor morphological modifications, although no inactivation of the cells was obtained. However, 5 min of SC-CO2+HPU treatment totally inactivated the population of both microorganisms. SC-CO2+HPU produced the degradation of the internal cell content and the disruption of the cell wall and plasmalemma, which prevented the possible regrowth of the cells during refrigerated storage.
Food Microbiology, 2010
In this study, the relationship between (irreversible) membrane permeabilization and loss of viability in Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae cells subjected to high pressure carbon dioxide (HPCD) treatment at different process conditions including temperature (35e45 C), pressure (10.5e21.0 MPa) and treatment time (0e60 min) was examined. Loss of membrane integrity was measured as increased uptake of the fluorescent dye propidium iodide (PI) with spectrofluorometry, while cell inactivation was determined by viable cell count. Uptake of PI by all three strains indicated that membrane damage is involved in the mechanism of HPCD inactivation of vegetative cells. The extent of membrane permeabilization and cellular death increased with the severity of the HPCD treatment. The resistance of the three tested organisms to HPCD treatment changed as a function of treatment time, leading to significant tailing in the survival curves, and was dependent on pressure and temperature. The results in this study also indicated a HPCD-induced damage on nucleic acids during cell inactivation. Transmission electron microscopy showed that HPCD treatment had a profound effect on the intracellular organization of the micro-organisms and influenced the permeability of the bacterial cells by introducing pores in the cell wall.
High carbon dioxide pressure inactivation kinetics of Escherichia coli in broth
Food Microbiology, 2001
The inactivation kinetics of Escherichia coli by high pressure carbon dioxide was investigated. Inactivation rates increased with increasing pressure (25, 50, 75 and 100 atm), temperature, and exposure time. Microbial inactivation followed ¢rst order reaction kinetics, with inactivation rates (k) and decimal reduction times (D) that varied from 0?0848 to 0?4717 min 71 and from 4?90 to 27?46 min, respectively, at treatment temperatures (20, 30 and 408C). The inactivation rates of E. coli were described by the apparent activation volume (DV*) and a 'pressure z value' , and they were greatly dependent on both temperature and pressure.
Microbiology, 2013
Foodborne illness due to bacterial pathogens is increasing worldwide as a consequence of the higher consumption of fresh and minimally processed food products, which are more easily crosscontaminated. The efficiency of food pasteurization methods is usually measured by c.f.u. plate counts, a method discriminating viable from dead cells on the basis of the ability of cells to replicate and form colonies on standard growth media, thus ignoring viable but not cultivable cells. Supercritical CO 2 (SC-CO 2 ) has recently emerged as one of the most promising fresh food pasteurization techniques, as an alternative to traditional, heat-based methods. In the present work, using three SC-CO 2 -treated foodborne bacteria (Listeria monocytogenes, Salmonella enterica and Escherichia coli) we tested and compared the performance of alternative viability test methods based on membrane permeability: propidium monoazide quantitative PCR (PMA-qPCR) and flow cytometry (FCM). Results were compared based on plate counts and fluorescent microscopy measurements, which showed that the former dramatically reduced the number of cultivable cells by more than 5 log units. Conversely, FCM provided a much more detailed picture of the process, as it directly quantifies the number of total cells and distinguishes among three categories, including intact, partially permeabilized and permeabilized cells. A comparison of both PMA-qPCR and FCM with plate count data indicated that only a fraction of intact cells maintained the ability to replicate in vitro. Following SC-CO 2 treatment, FCM analysis revealed a markedly higher level of bacterial membrane permeabilization of L. monocytogenes with respect to E. coli and S. enterica. Furthermore, an intermediate permeabilization state in which the cellular surface was altered and biovolume increased up to 1.5-fold was observed in L. monocytogenes, but not in E. coli or S. enterica. FCM thus compared favourably with other methods and should be considered as an accurate analytical tool for applications in which monitoring bacterial viability status is of importance, such as microbiological risk assessment in the food chain or in the environment.