Development of a phage typing system for Staphylococcus hyicus

First Molecular Characterization of Siphoviridae-Like Bacteriophages Infecting Staphylococcus hyicus in a Case of Exudative Epidermitis

Exudative epidermitis (EE), also known as greasy pig disease, is one of the most frequent skin diseases affecting piglets. Zoonotic infections in human occur. EE is primarily caused by virulent strains of Staphylococcus (S.) hyicus. Generally, antibiotic treatment of this pathogen is prone to decreasing success, due to the incremental development of multiple resistances of bacteria against antibiotics. Once approved, bacteriophages might offer interesting alternatives for environmental sanitation or individualized treatment, subject to the absence of virulence and antimicrobial resistance genes. However, genetic characterization of bacteriophages for S. hyicus has, so far, been missing. Therefore, we investigated a piglet raising farm with a stock problem due to EE. We isolated eleven phages from the environment and wash water of piglets diagnosed with the causative agent of EE, i.e., S. hyicus. The phages were morphologically characterized by electron microscopy, where they appeared Siphoviridae-like. The genomes of two phages were sequenced on a MiSeq instrument (Illumina), resulting in the identification of a new virulent phage, PITT-1 (PMBT8), and a temperate phage, PITT-5 (PMBT9). Sequencing of three host bacteria (S. hyicus) from one single farm revealed the presence of two different strains with genes coding for two different exfoliative toxin genes, i.e., exhA (2 strains) and exhC (1 strain). The exhC-positive S. hyicus strain was only weakly lysed by most lytic phages. The occurrence of different virulent S. hyicus strains in the same outbreak limits the prospects for successful phage treatment and argues for the simultaneous use of multiple and different phages attacking the same host.

Genomics of staphylococcal Twort-like phages--potential therapeutics of the post-antibiotic era

Polyvalent bacteriophages of the genus Twort-like that infect clinically relevant Staphylococcus strains may be among the most promising phages with potential therapeutic applications. They are obligatorily lytic, infect the majority of Staphylococcus strains in clinical strain collections, propagate efficiently and do not transfer foreign DNA by transduction. Comparative genomic analysis of 11 S. aureus/S. epidermidis Twort-like phages, as presented in this chapter, emphasizes their strikingly high similarity and clear divergence from phage Twort of the same genus, which might have evolved in hosts of a different species group. Genetically, these phages form a relatively isolated group, which minimizes the risk of acquiring potentially harmful genes. The order of genes in core parts of their 127 to 140-kb genomes is conserved and resembles that found in related representatives of the Spounavirinae subfamily of myoviruses. Functions of certain conserved genes can be predicted based on their homology to prototypical genes of model spounavirus SPO1. Deletions in the genomes of certain phages mark genes that are dispensable for phage development. Nearly half of the genes of these phages have no known homologues. Unique genes are mostly located near termini of the virion DNA molecule and are expressed early in phage development as implied by analysis of their potential transcriptional signals. Thus, many of them are likely to play a role in host takeover. Single genes encode homologues of bacterial virulence-associated proteins. They were apparently acquired by a common ancestor of these phages by horizontal gene transfer but presumably evolved towards gaining functions that increase phage infectivity for bacteria or facilitate mature phage release. Major differences between the genomes of S. aureus/S. epidermidis Twort-like phages consist of single nucleotide polymorphisms and insertions/deletions of short stretches of nucleotides, single genes, or introns of group I. Although the number and location of introns may vary between particular phages, intron shuffling is unlikely to be a major factor responsible for specificity differences.

Differentiation and distribution of three types of exfoliative toxin produced by Staphylococcus hyicus from pigs with exudative epidermitis

Exfoliative toxins of approximately 30 kDa produced by Staphylococcus hyicus strains NCTC 10350, 1289D-88 and 842A-88 were purified and specific polyclonal antisera were raised against each of the toxins. It was shown by immunoblot analysis and ELISA that three exfoliative toxins from S. hyicus were antigenically distinct. The three toxins were designated ExhA, ExhB and ExhC. From 60 diseased pigs, each representing an outbreak of exudative epidermitis, a total of 584 isolates of S. hyicus were phage typed and tested for production of exfoliative toxin. ExhA-, ExhB- and ExhC-producing S. hyicus isolates were found in 12 (20%), 20 (33%) and 11 (18%), respectively, of the 60 pig herds investigated. Production of the different types of exfoliative toxin was predominantly associated with certain phage groups. However, toxin production was found in all of the six phage groups defined by the phage typing system. Some changes in the distribution of isolates between phage groups were observed when the results of this study were compared to previous investigations. In this study two new antigenically distinct exfoliative toxins were isolated and tools for in vitro detection of toxin producing S. hyicus isolates and for further studies on the exfoliative toxins from S. hyicus have been provided.