Characterisation of bacteriophages infecting the Bacillus cereus group

Details

Supervisors

Gillis, Annika

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

This study aimed to characterise three bacteriophages Alexis, Helenis, and Lasnis isolated from wastewater treatment plants of Rixensart, and to assess their efficacy as biocontrol agents against Bacillus cereus group strains. This research was undertaken to explore alternatives to traditional antibiotics due to the increasing problem of antibiotic resistance. Bacteriophages, viruses that infect and lyse bacteria, have emerged as potential biocontrol agents due to their specificity and effectiveness against bacterial pathogens. The study was set in the context of finding sustainable and effective methods to control harmful Bacillus strains. The Bacillus cereus group includes species that are significant in both clinical and environmental settings, with implications for food safety and public health. The study involved several key methodologies. First, phages were isolated from wastewater samples and purified using standard techniques to obtain high-titer stocks. Secondly, the stability of phages at various temperatures, ranging from 4°C to 100°C, was assessed through thermal stability assays to determine their suitability for different environmental conditions. Thirdly, pH stability assays were conducted to assess the robustness of phages across a pH range of 2 to 13, aiming to comprehend their resilience in diverse pH conditions. Fourthly, the ability of the phages to infect different Bacillus strains was tested in host range determination experiments to evaluate their potential for broad- spectrum application. Additionally, the bactericidal activity of the phages against Bacillus thuringiensis GSX002 was measured at different phage-to-bacteria ratios in killing assays. Lastly, the replication dynamics and lytic activity of the phages were studied through a one-step growth curve to understand their infection kinetics. Future research should focus on optimising the formulation and delivery of these phages to enhance their stability and efficacy in various conditions. Genetic engineering of phages to enhance their lytic activity and host range, as well as combining phages with other antimicrobial agents, could offer innovative solutions to bacterial infections and resistance. Additionally, large-scale production methods and direct trials in the food industry are necessary to validate the practical applications of these phages. By addressing these aspects, this study contributes to the ongoing efforts to develop effective and sustainable alternatives to antibiotics, potentially reducing the impact of antibiotic resistance and improving food safety and public health.