• Antibiofilm activity
• Antimicrobial activity
• Antimicrobial resistance
• Bacteriophages
• Genotypic characterization
• Nosocomial infections
• Phage therapy
• Phenotipic characterization
• Phylogenetic study
• Staphylococcus epidermidis

Thirteen clinical S. epidermidis strains were isolated from eleven patients with difficult-to-treat musculoskeletal infections (treated at University hospitals Leuven, Belgium) with the aim of characterizing them genomically to identify antibiotic resistance genes, defense mechanisms, virulence factors and the presence of prophages. Moreover, a comparative core genome analysis was performed to establish whether different commensal and pathogenic S. epidermidis strains were specifically clustered.
Subsequently, the host range of 22 different Staphylococcus phages (vB_SepM_BE06, phiIPLA-C1C, SE-02 B, SE-02 D, CUB-EPI_14, ISPepi, ISP, Romulus, Remus, Zeno, eight mutants of Zeno, LG, MG, LP and MP) was tested on S. epidermidis clinical isolates showing that three S. epidermidis can eradicate a broad range of tested S. epidermidis strains. The host range of SE-02 B and SE-02 D phages was also tested on other strains of Staphylococcus species different from S. epidermidis intending to test their ability to infect different bacterial species, showing that they were able to infect only the strain Staphylococcus schleiferi RO.
In order to understand if recently isolated and uncharacterized S. epidermidis bacteriophages SE-02 B and SE-02 D could be used to eradicate difficult-to-treat infections, phenotypic and genotypic analyses were performed. The one-step growth curve assays show the kinetic of infection of phages to their host. Both analyzed phages showed a latent period of around 20-30 minutes and a burst size of approximately 10^5 PFU/mL. Lysis kinetic assays against planktonic and biofilm-embedded cells of S. epidermidis were performed to investigate the interaction between SE-02 B and SE-02 D phages and four clinical bacterial strains selected according to their high susceptibility to these phages. Both phages displayed a significant lytic activity on planktonic cells on most tested strains, especially at higher concentrations, but they did not show an antibiofilm activity. As for the genomic data, these bacteriophages turned out to be putatively suitable for phage therapy since they did not have any indication of temperate behavior, antibiotic resistance, or virulence.
The recently isolated phages CUB-EPI_14, LG, MG, LP, and MP were also analyzed genomically, as well as taxonomically, and four of them were clustered into new viral species. Also in this case, they resulted potentially suitable for phage therapy.
At last, a bioinformatic SNPs analysis identified mutations of adapted S. aureus ISP phage (ISPepi) to a specific S. epidermidis strain. These were concerned with phage-bacteria interaction proteins and a DNA repair enzyme.