| Streptococcus equi (S. equi) causes equine strangles, an acute highly contagious suppurative lymphadenopathy of the head and neck. Since integrated phages in many bacterial genomes have been shown to impact virulence and other host characteristics, the temperate bacteriophage of S. equi has been characterized, sequenced and annotated. A member of Siphoviridae, SeP9 has an icosahedral capsid and a long non-contractile tail and contains a double-stranded DNA genome. Its DNA sequence consists of 40,539 bp, encodes 54 putative open reading frames (ORFs) and shares close similarity to Streptococcus pyogenes phage 315.6. The genome is organized in modules for lysogeny, DNA replication, transcriptional regulation, DNA packaging, head, head-tail joining, tail, tail fiber, lysis and lysogenic conversion. SeP9 encodes a hyaluronidase and putative streptodornase that may contribute to virulence. The phage is integrated at a site in S. equi e21 corresponding to position 492214 bp in S. equi 4047. The receptor for SeP9 is the Lancefield group C carbohydrate antigen. Remarkably, S. zooepidemicus is not infected, although the extracted carbohydrate antigen of S. zooepidemicus binds the phage. The phage associated lysin of SeP9 (PlySe) encoded by ORF 51 (1203 bp) was expressed in E. coli and purified. Based on deduced amino acid sequence, PlySe has a molecular mass of 44.2 kDa, a theoretical pI value of 4.74 and shares 90% identity with lysins from other Streptococcus spp. In vitro PlySe activity was tested on a series of isolates of S. equi and other streptococcal spp. and in pus from abscesses caused by S. equi. The observed highly significant decrease in OD as well as in colony forming units supports the potential of PlySe as an antibacterial agent.; Keywords. Streptococcus equi, bacteriophage, genome sequence, receptor, lysin... |
