Characterisation of Strains and Their Prophages That Carry Horse-Specific Leukocidin Genes .

Leukocidins of (.) are bicomponent toxins that form polymeric pores in host leukocyte membranes, leading to cell death and/or triggering apoptosis. Some of these toxin genes are located on prophages and are associated with specific hosts. The genes have been described from equine isolates. We examined the genomes, including the prophages, of strains belonging to clonal complexes CC1, CC350, CC816, and CC8115. In addition to sequencing, phages were characterised by mitomycin C induction and transmission electron microscopy (TEM). All prophages integrated into the = gene, and all included also the gene encoding an equine staphylococcal complement inhibitor. The prophages clustered, based on gene content and allelic variants, into three groups. One was found in CC1 and CC97 sequences; one was present mainly in CC350 but also in other lineages (CC1, CC97, CC133, CC398); and a third one was exclusively observed in CC816 and CC8115. Prophages of the latter group additionally included a rare enterotoxin A allele (). Moreover, a prophage from a CC522 goat isolate was found to harbour . Its component could be regarded as chimaera comprising parts of and of . A putative kinase gene of 1095 basepairs was found to be associated with equine strains of . It was also localised on prophages. However, these prophages were different from the ones that carried , and three different integration sites of kinase-carrying phages were identified. These observations confirmed the presence of prophage-located important virulence-associated genes in equine and that certain prophages might determine the host specificity of the staphylococcal strains they reside in.