Comparison of Effects of Sublethal Microwave Radiation and Conventional Heating on the Metabolic Activity of Staphylococcus aureus

Abstract

This study was conducted in an attempt to characterize some of the effects of sublethal microwave radiation on cells of Staphylococcus aureus. Cultures were exposed to microwave radiation for 10, 20, 30, and 40 s. The effects of a conventional heat treatment were also compared by placing flasks containing cultures in a boiling water bath for the amount of time required to reach temperatures equivalent to those found in cultures exposed to microwave radiation. Control, microwave-treated, and conventionally heat-treated cultures were centrifuged, pellets were resuspended in distilled water, and the resulting suspensions were passed through a French pressure cell. Cell lysates and walls were then isolated and assayed for enzymatic activity. Thermonuclease production was also determined at various levels of exposure of cells to microwave radiation. Activities of malate and α-ketoglutarate dehydrogenases, cytochrome oxidase, and cytoplasmic adenosine triphosphatase were higher in microwave-treated cells than in control cells. Membrane adenosine triphosphatase, alkaline phosphatase, and lactate dehydrogenase activities were unaffected when cells were exposed to microwave radiation. The activity of glucose-6-phosphate dehydrogenase was decreased by exposure of cells to microwave radiation. In conventionally heated cells, activities of glucose-6-phosphate and malate dehydrogenases and cytoplasmic adenosine triphosphatase increased activities of α-ketoglutarate and lactate dehydrogenases decreased, and alkaline phosphatase activity remained unaffected. Increased levels of thermonuclease activity were observed when cells were exposed to microwave radiation for 10 or 20 s. Data indicate that microwave radiation affects S. aureus in a manner which cannot be explained solely by thermal effects.

Continuous-Flow Microwave Inactivation Kinetics of Pectin Methyl Esterase in Orange Juice

“…In other words, these results confirm the contributory nonthermal effects of microwaves resulting in enhanced inactivation of PME in orange juice as also observed in our previous study (Tajchakavit and Ramaswamy 1995). There (Dreyfuss and Chipley 1980;Khalil and Villota 1988). Some possible mechanisms for the nonthermal effects of microwaves which will most likely be explained as structural changes in a microscopic and molecular level, have been detailed in Olsen et ul.…”

Microwave assisted nanofibrous air filtration for disinfection of bioaerosols

“…Meanwhile, other studies have reported their observations of non-thermal effect during microwave disinfection of microorganisms. They distinguished the non-thermal effect through examination of damaged cells (Campanha et al, 2007;Celandroni et al, 2004), distorted membrane structure and function (Persson, Salford, Brun, Eberhard, & Malmgren, 1992;Phelan, Neubauer, Timm, Neirenberg, & Lange, 1994), increased release of Ca 2 + , K + , DNA, dipicolinic acid and protein (Campanha et al, 2007;Celandroni et al, 2004;Vaid & Bishop, 1998) and altered the enzyme activities (Dreyfuss & Chipley, 1980) after microwave irradiation. Betti et al (2004) acknowledged the disruption of weak bonds in active protein forms, enhanced production of reactive oxygen species, and cell-signaling pathway interference to microwave non-thermal effects.…”

Microwave-induced release and degradation of airborne endotoxins from Escherichia coli bioaerosol

“…S5). High temperatures can cause denaturation and cell membrane damage [34], as well as alter enzymatic activities by disrupting weak bonds in active protein forms [35]. Moreover, MW irradiation exerts nonthermal effects on cell viability by interfering with cell signaling pathways, generating current within cells [36], and producing reactive oxygen species such as % OH [37].…”

“…Similar finding was observed by Wu et al [8] that the microwave-irradiated P. fluorescens cells apparently had damaged membrane envelope as observed in the SEM images. Previous researches showed that MW can alter enzymatic activities by disrupting weak bonds in active protein forms [38], and produce reactive oxygen species (such as % OH) [37], which was used to damage membrane envelope. The SEM images of E. coli cells before and after MW irradiation ( Fig.…”