Investigations Into the Suitability of Bacterial Suspensions as Biological Indicators for Low-Energy Electron Irradiation

Abstract

Low-energy electron irradiation is an emerging alternative technology for attenuated or complete pathogen inactivation with respect to medical, biotechnological, and pharmaceutical applications. Pathogen inactivation by ionizing radiation depends mainly on the absorbed electron dose. In low-energy electron irradiation processes, determination of the absorbed electron dose is challenging due to the limited, material-dependent penetration depth of the accelerated electrons into the matter. In general, there are established dosimetry systems to evaluate the absorbed dose under dry irradiation conditions. However, there is no system for precise dose monitoring of low-energy irradiation processes in liquids or suspensions so far. Therefore, in this study three different bacterial species were investigated as biological dose indicators, especially in the range of low doses (< 6.5 kGy) in aqueous solutions or suspensions. Escherichia coli, Bacillus subtilis, and Staphylococcus warneri were comparatively evaluated for their suitability as biological dose indicators. Thin homogeneous films of the respective bacterial suspensions were irradiated with increasing doses of low-energy accelerated electrons. The average absorbed dose was determined using a colorimetric dosimeter based on a tetrazolium salt solution. The maximum and minimum absorbed doses were measured with a referenced film dosimeter. Subsequently, the inactivation kinetics was determined in terms of inactivation curves and D10 values. Thus, the minimum inactivation dose of bacterial growth was assessed for E. coli and S. warneri. The effect of irradiation with low-energy accelerated electrons on the growth behavior and activity of the bacteria was studied in more detail using impedance spectroscopy. With increasing irradiation doses growth was delayed.

Hemoglobin Derivatives in Beef Irradiated with Accelerated Electrons

“…Figure 6c shows the dependencies of C metHb in the beef samples irradiated with the doses D 1 and D 2 calculated using Formula (11), which align with the experimental results presented in [35] and attest to the relevance of the Verhulst model used to describe the kinetics of bacteria populations in irradiated samples.…”

“…The second reason for the formation of metHb in the beef samples is the biochemical and biophysical processes caused by bacterial activity. As shown in papers [33,34], the concentrations of microorganisms in meat and poultry, as well as the bacterial content in nutrient solutions [35], increase sigmoidally as the storage time passes; moreover, the rate of bacterial growth depends on a number of factors, such as the initial bacterial content, number and types of bacteria populations, storage temperature, and nutrients [36]. In addition, the sigmoidal character of the dependency of bacterial content on the storage time can also be observed after irradiation, and the rate of bacterial growth decreases with an increase in the dose applied [33].…”

Mucosal Application of a Low-Energy Electron Inactivated Respiratory Syncytial Virus Vaccine Shows Protective Efficacy in an Animal Model

“…The absorbed dose applied was estimated by using a liquid dosimeter based on 2,3,5-triphenyl-tetrazolium chloride (TTC, Carl Roth, Karlsruhe, Germany), which undergoes colorization due to a dose-dependent reaction to red formazan, as described in the study of Schopf et al [ 65 ]. Previously, a calibration function to convert absorbance values into dose was found with a combined uncertainty of 11.8% in the dose range of 6.5–38 kGy.…”

Liquid dosimeter with sensitivity in low-kGy range for the characterization of a new module for EB wastewater treatment

“…Due to EB's ability to partially or completely inactivate pathogens at signifi cantly lower energies, it has become an emerging alternative technology in many medical, biotechnological, and pharmaceutical applications [5]. The use of low-energy electrons has several advantages over traditional methods.…”