Physiological changes of Escherichia coli O157:H7 and Staphylococcus aureus following exposure to high hydrostatic pressure

Yousef, Ahmed
Alpas, Hami
Morphological changes and membrane integrity of Escherichia coli O157:H7 and Staphylococcus aureus cells before and after high hydrostatic pressure (HHP) treatments (200-400 MPa) and time (1-5 min), at a constant temperature (40 A degrees C), in peptone water were examined by using scanning electron microscopy (SEM) and fluorescent microscopy, respectively. SEM images showed that unpressurized cells exhibited a smooth surface appearance. E. coli O157:H7 cells exposed to pressure treatments first appeared larger, then with increasing pressure distorted with dimples and pinches. In case of S. aureus, the cells pressurized at low pressure levels did not show any significant change. The surface appearance became rough and cracked when the cells were exposed to higher pressure levels. Images of fluorescent microscopy showed that a small proportion of bacterial cells were not green fluorescent at lower pressure levels. The other part of the cell population was red fluorescent representing dead cells and the number of red fluorescent cells increased with increasing pressure. The cells with a yellowish color showed that varying levels of membrane damage occurred under HHP. The combinations of mild heat, antimicrobial substances and HHP treatment can be used to inactivate food borne pathogens of varying pressure resistance in the food industry for safe processing conditions. However, the resultant damaged cells at different levels should be taken into account during storage to prevent their recovery.


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DAMAR, SİBEL; Bozoglu, F; Hizal, MİRZAHAN; Bayındırlı, Alev (2002-02-01)
Two pathogenic microorganisms Escherichia coli O157:H7 and Staphylococcus aureus, suspended in peptone solution (0.1% w/v) were treated with 12, 14, 16 and 20 kV/cm electric field strengths with different pulse numbers up to 60 pulses. Pulsed electric field (PEF) treatment at 20 kV/cm with 60 pulses provided nearly 2 log reduction in viable cell counts of E. coli O157:H7 and S. aureus. S. aureus cells were slightly more resistant than E.coli O157:H7 cells. The results related to the effect of initial cell c...
Development of a new mathematical model for inactivation of Escherichia coli O157:H7 and Staphylococcus aureus by high hydrostatic pressure in carrot juice and peptone water
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Survival data of Escherichia coli O157:H7 933 and Staphylococcus aureus 485 in carrot juice and peptone water were collected in a range of pressure levels between 200 and 400 MPa at 40 degrees C. A mathematical approach combining the primary and secondary models (Weibull and first-order models as the primary model and two empirical equations as the secondary model) was proposed to estimate the microbial parameters using nonlinear least squares procedure in one step, resulting a single equation. Although not...
The combined effect of high hydrostatic pressure, heat and bacteriocins on inactivation of foodborne pathogens in milk and orange juice
Alpas, Hami (2000-06-01)
The objective of this study was to combine pressure (345 MPa) with heat (50 degrees C), and bacteriocins (5000 AU/ml sample) for a short time (5 min) for the inactivation of relatively pressure-resistant strains of four foodborne pathogens: Staphylococcus aureus, Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella in pasteurized milk and orange juice. Without bacteriocin addition, 5.5 log-cycle reduction was obtained for S. aureus 485 in milk whereas more than 8 log-cycle reduction was achieved ...
Secondary structure and conformational change of mushroom polyphenol oxidase during thermosonication treatment by using FTIR spectroscopy
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To understand the conformational changes of mushroom PPO, the secondary structural change of the enzyme during thermosonication treatment at different power (60, 80 and 100%), temperature (20-60 degrees C) and time (0-30 min) combinations was investigated by using FTIR spectroscopy and compared with the change in enzyme activity. The enzyme inactivation higher than 99% was obtained at 100% amplitude at 60 degrees C for 10 min. FTIR studies showed that marked spectral changes were noted after ultrasound trea...
Evaluation of high hydrostatic pressure sensitivity of Staphylococcus aureus and Escherichia coli O157 : H7 by differential scanning calorimetry
Alpas, Hami; BOZOGLU, F; KALETUNC, G (Elsevier BV, 2003-11-01)
Differential scanning calorimetry (DSC) was used to evaluate the relative high hydrostatic pressure (HHP) resistances of bacterial strains from Staphylococcus aureus and Escherichia coli O157:H7 in vivo. The total apparent enthalpy change and thermal stability were two DSC parameters used to compare bacterial strains of untreated control and pressure-treated bacteria. DSC thermograms indicated that ribosomal denaturation appears to be a major factor in cell death by both thermal and high pressure treatments...
Citation Formats
M. ÇELİK, A. Yousef, and H. Alpas, “Physiological changes of Escherichia coli O157:H7 and Staphylococcus aureus following exposure to high hydrostatic pressure,” JOURNAL FUR VERBRAUCHERSCHUTZ UND LEBENSMITTELSICHERHEIT-JOURNAL OF CONSUMER PROTECTION AND FOOD SAFETY, pp. 175–183, 2013, Accessed: 00, 2020. [Online]. Available: