Comparative virulome analysis of four Staphylococcus epidermidis strains from human skin and platelet concentrates using whole genome sequencing

Staphylococcus epidermidis is one of the predominant bacterial contaminants in platelet concentrates (PCs), a blood component used to treat bleeding disorders. PCs are a unique niche that triggers biofilm formation, the main contributor to S. epidermidis infections. We performed whole genome sequencing of four S. epidermidis strains isolated from the skin of healthy human volunteers (AZ22 and AZ39) and contaminated PCs (ST10002 and ST11003) to unravel phylogenetic relationships and decipher virulence mechanisms compared to 25 complete S. epidermidis genomes in GenBank. AZ39 and ST11003 formed a separate unique lineage with 14.1.R1 and SE95 strains, while AZ22 formed a cluster with 1457 and ST10002 closely grouped with FDAAGOS_161. The four isolates were assigned to sequence types ST1175, ST1174, ST73, and ST16, respectively. All four genomes exhibited biofilm-associated genes ebh, ebp, sdrG, sdrH, and atl. Additionally, AZ22 had sdrF and aap, whereas ST10002 had aap and icaABCDR. Notably, AZ39 possesses truncated ebh and sdrG and harbors a toxin encoding gene. All isolates carry multiple antibiotic resistance genes conferring resistance to fosfomycin (fosB), β-lactams (blaZ) and fluoroquinolones (norA). This study revealed a unique lineage for S. epidermidis and provided insight into the genetic basis of virulence and antibiotic resistance in transfusion-associated S. epidermidis strains.