Effect of microwave radiation on Bacillus subtilis spores

Abstract

Aims:To compare the killing efficacy and the effects exerted by microwaves and conventional heating on structural and molecular components of Bacillus subtilis spores. Methods and Results: A microwave waveguide applicator was developed to generate a uniform and measurable distribution of the microwave electric-field amplitude. The applicator enabled the killing efficacy exerted by microwaves on B. subtilis spores to be evaluated in comparison with conventional heating at the same temperature value. The two treatments produced a similar kinetics of spore survival, while remarkably different effects on spore structures were seen. The cortex layer of the spores subjected to conductive heating was 10 times wider than that of the untreated spores; in contrast, the cortex of irradiated spores did not change. In addition, the heated spores were found to release appreciable amounts of dipicolinic acid (DPA) upon treatment, while extracellular DPA was completely undetectable in supernatants of the irradiated spores. These observations suggest that microwave radiation may promote the formation of stable complexes between DPA and other spore components (i.e. calcium ions); thus, making any release of DPA from irradiated spores undetectable. Indeed, while a decrease in measurable DPA concentrations was not produced by microwave radiation on pure DPA solutions, a significant lowering in DPA concentration was detected when this molecule was exposed to microwaves in the presence of either calcium ions or spore suspensions. Conclusions: Microwaves are as effective as conductive heating in killing B. subtilis spores, but the microwave E-field induces changes in the structural and/or molecular components of spores that differ from those attributable only to heat. Significance and Impact of the Study: This study provides information on the effect of microwaves on B. subtilis spore components.

Effect of Microwave Treatment on Microbial Contamination of Honeys and in Their Physicochemical and Thermal Properties

“…Consequently, microwave radiation is regarded as an alternative method for killing bacteria because of its effectiveness, commercial availability, and lower cost compared with other technologies [Celandroni et al, 2004]. However, the effect of microwave on bacteria depends on food composition and type of microorganism [Castro et al, 1997].…”

“…Microwave radiation cannot be thought as simple heating from the inside; the E-fi eld would produce effects on the biological molecules affecting spore structure, different from those attributable only to heat [Celandroni et al, 2004]. Gamma radiation method was used to control this disease, in order to inactivate P. larvae, although signifi cant effect on chemical parameters and enzyme activities of honey were observed [Baggio et al, 2005].…”

Microwave-irradiation-assisted HVAC Filtration for Inactivation of Viral Aerosols

“…Meanwhile, there has been research demonstrating additional effects, beyond the purely thermal mode of inactivation. For example, distortion of membrane structure and function (Phelan et al, 1994), altered enzyme activity (Dreyfuss and Chipley, 1980), disruption of weak bonds (Betti et al, 2004), increased release of various substances (Woo et al, 2000;Celandroni et al, 2004;Campanha et al, 2007), and increased ionic strength due to an increased current within cells (Watanabe et al, 2000) have all been reported. However, all of the aforementioned research was conducted in the liquid, solid, or aqueous phase.…”

Levels of Ca 2+ -Dipicolinic Acid in Individual Bacillus Spores Determined Using Microfluidic Raman Tweezers

“…This latter potential variation could be important, since a spore's DPA content can markedly influence its resistance properties, as noted above, and thus variations in Ca-DPA content might be correlated with heterogeneity in resistance properties of spores in a population. Generally only spore populations' DPA contents have been determined, by boiling or autoclaving large numbers of spores for 15 to 30 min, centrifuging, and measuring the DPA in the supernatant fluid either chemically or by the optical density at 270 nm (4,23,26). Ca-DPA in single spores has been detected using Raman spectroscopy (5,6), but there have not been extensive measurements of Ca-DPA in single spores of various species and strains, as well as in individual spores in a population.…”