Characterization of the lytic activity of bacteriophages against Shigella dysenteriae

Abstract

Introduction: Shigella dysenteriae is endemic in most regions of most developing countries including Uganda. Emergence of increased levels of multi-drug resistant Shigella dysenteriae strains has become worrisome in the clinical field. Isolating and characterizing bacteriophages as alternatives to antibiotics in the treatment of Shigella infection hold promise in mitigating this problem by reducing the morbidity and mortality rates especially in children below five years. Objectives: To establish and characterize a stock of crude specific virulent bacteriophages against Shigella dysenteriae strains. Methodology: This study employed experimental laboratory-based studies to isolate phages from latrine effluents, which were purified and quantified. Two cryopreserved Shigella dysenteriae isolates were resuscitated and used as bacterial hosts for the isolation of bacteriophages. The isolated bacteriophages were characterized to determine their invitro lytic activity against different hosts which included the Shigella dysenteriae strains, Escherichia coli, Proteus spp, Salmonella spp and S. aureus, at different temperatures and pH. A one-step growth curve experiment was performed to determine the latent time and Number of bacteriophage progenies produced per cycle (burst size). Results: In this study, two bacteriophages (designated Sd1 and Sd2) with lytic activity against Shigella dysenteriae were isolated and purified from latrine effluent samples. The phages were found to have a narrow host range, working best in a temperature range of 4°C to 37°C and pH of 6.0 to 8.0. Phage Sd1 had a latent period of 25 minutes and burst size of 631 progenies per cell while Phage Sd2 had a latent period of 30 minutes and burst size of 229 progenies per cell. Conclusion: The phages exhibited lytic activity and some stability at conditions where Shigella dysenteriae is commonly encountered, however more evaluations are recommended before application for environmental decontamination of Shigella dysenteriae affected communities and phage therapy