Isolation and Characterization of Bacteriophage Streptococcus equi for Application against Horse Strangles

Abstract

Horse strangles is an acute infectious disease that manifests itself sporadically, enzootically, and epizootically and is widespread in Kazakhstan, where it mainly affects foals and young horses. The causative agent of strangles is the bacterium Streptococcus equi. In conditions of global antibiotic resistance, bacteriophages can become an effective means of treating horse stranglers. The research aim is to develop a new phage therapy against horse strangles using a local test strain of Streptococcus equi, namely bio-material isolated from a foal with strangles. When working with bacteriophages, the following methods were used: the Appelman (serial dilutions) and Grazia (agar layers) methods were used the isolation of bacteriophages and nutrient media GRM agar and GRM broth were used for the cultivation of bacteria and their phages. As a result, 6 bacteriophages were isolated from the studied 117 samples from the collected samples, after studying their basic biological properties, it was decided in further work to select the 1 most active bacteriophage specific to Streptococcus equi. This 1 bacteriophage was sequenced and registered in the Streptococcus phage BV0002 GenBank "Bank It2666451 Bacteriophagum OQ319049" (https://www.ncbi.nlm.nih.gov/nuccore/OQ319049). Genome-wide sequencing was performed on an automatic genome-wide sequencer Ion Torrent (Thermo Fisher Scientific, using the Ion XpressPlus Fragment Library Kit (Waltham, MA, USA). As a result, taking into account the highest percentage of identity of the analysed sequence in the international database using the BLAST algorithm, as well as the results of phylogenetic analysis, it was found that the selected bacteriophage belongs to the family Myoviridae, characteristic of the species Bacteriophagum Streptococcus equi.