engleski

Stress response of Escherichia coli K12 after the gas phase electrical discharge plasma treatment

Nowadays one of major problem are the foodborne outbreaks. Potential hazard to human health is not only due to physical or chemical properties, but also due to biological one (1). Escherichia coli, especially E.coli with O groups: O26, O103, O111, O145 and O157 can cause human gastrointestinal diseases and is responsible for many deaths (2). New nonthermal technologies such as pulsed electric field, high pressure and high voltage electrical discharges are in developing process due to their inactivation characteristics. Plasma defined as ionized gas is consisted of atoms, molecules, radicals, ions and electrons which in combination are responsible for germicidal effect (3). The aim of this work was to examine the inactivation rate and stress response of treated E.coli K12 cells inoculated in aqueous suspension, after the gas phase plasma treatment. Determination of cellular leakage, biofilm formation, degree of recovery and concentration of H2O2 were conducted in order to determine stress response of E.coli. Statgraphics Centurion software (StatPoint Technologies, Inc., VA, USA) was used for experimental design and statistical analyses. Conductivity (100 and 800 µS/cm), polarity (- ; +), frequency (60, 90, 120 Hz) and time (5 and 10 min) were change in order to determine their influence on listed parameters. The laboratory high voltage electrical discharge system was consisted of glass vessel of 1 L, appropriate teflon cap, stainless steel ground electrode (diameter of 4.5 cm) and titanium high voltage electrode. Argon (purity 99.99 %) was injected in headspace of reactor. Treated volume was 200 mL. Initial pH of sample was 7.00±0.05. The greatest reduction (7.8 log reduction) was achieved after the 10 min of treatment, 90 Hz, positive polarity and conductivity of 100 µS/cm. Measured pH level was 3.2 but after the 18 h percentage of recovery was 100 %. The highest measured concentration of H2O2 was after the mentioned treatment (90 Hz, 10 min, +, 100 µS/cm). Biofilm formation was not completely reduced, as all the samples gave increase in percentage of recovery. Also with a longer treatment time increase in cellular leakage was observed. Synergistic effects of polarity, treatment time, solution conductivity, pH and concentration of free radicals could have influence on inactivation rate of E. coli, but further optimization of method is needed to understand why the recovery of cell occurs.

plasma ; E. coli ; stress response

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