Diversity of Vibrio Cholerae Bacteriophages From Lake Victoria, Coastal and Central Regions of Kenya and Assessment Of Their Potential as Bio Control Agents Against the Pathogen

Abstract

Cholera, a devastating diarrheal disease that accounts for more than 10% of children’s deaths worldwide, has persistently remained a health threat to world’s population at large. It is endemic in many countries and in Sub-Saharan Africa, prevention has not achieved much because the causative agent, Vibrio cholerae has emerged to be resistant to antibiotics that were previously efficacious towards the bacteria. Previous research has shown that phages may offer an alternative plausible biological control method for management of cholera. In this study potential exploitation of bacteriophages as antimicrobials to control toxigenic Vibrio cholerae El Tor was evaluated. The goal of the study was to isolate novel lytic Vibrio cholerae bacteriophages from environmental water sources of Kenya that included: Lake Victoria region, Coastal region, Nairobi and Central regions. Pathogenic Vibrio cholerae El Tor was isolated from these environmental water sources and used as the respective propagating strain for isolation of phages. Polymerase chain reaction amplification and sequencing of partial 16S ribosomal RNA gene was used for identification of the bacteria. In total, 140 surface water samples were obtained from ponds, rivers, lake, beaches, boreholes, springs, wells and Indian Ocean. Lytic spectrum confirmed that all the 15 phages displayed a lytic activity against different environmental Vibrio cholerae strains as well as a clinical strain. Further characterization by Transmission Electron Microscope assigned the vibriophages to order Caudovirales of Myoviridae family owing to their icosahedral capsids and contractile tails. From a total of 15 vibriophages, 4 were selected for complete nucleotide genome sequencing using various bioinformatic tools and restriction digestion profiles. The four full, linear phage genomes: vB_Vch4M_Ke, vB_Vch6M_Ke, vB_Vch18M_Ke, and vB_Vch24M_Ke had highly similar genome sizes of 148180bp, 148181bp, 148179, and 148179bp respectively, 4 tRNAs each, same G+C content of 36.4% and similar molecular weight of approximately 91.54MDa. The four genomes carried the phoH gene, which is

overrepresented in marine cyanophages. The bacteriophage, vB_VchM_Kuja complete genome sequence was deposited in the NCBI nucleotide databank and assigned; MN718199.1 as the accession number and corresponding Refseq record is: NC048827.1. It was assigned to the subfamily Ackermannviridae according to the current classification of viruses. These novel lytic vibriophages represent potential biocontrol candidates for water decontamination against pathogenic Vibrio cholerae and ought to be considered for future studies of phage therapy.