Isolation and in vitro characterization of novel S. epidermidis phages for therapeutic applications

Abstract

S. epidermidis is an important opportunistic pathogen causing chronic prosthetic joint infections associated with biofilm growth. Increased tolerance to antibiotic therapy often requires prolonged treatment or revision surgery. Phage therapy is currently used as compassionate use therapy and continues to be evaluated for its viability as adjunctive therapy to antibiotic treatment or as an alternative treatment for infections caused by S. epidermidis to prevent relapses. In the present study, we report the isolation and in vitro characterization of three novel lytic S. epidermidis phages. Their genome content analysis indicated the absence of antibiotic resistance genes and virulence factors. Detailed investigation of the phage preparation indicated the absence of any prophage-related contamination and demonstrated the importance of selecting appropriate hosts for phage development from the outset. The isolated phages infect a high proportion of clinically relevant S. epidermidis strains and several other coagulase-negative species growing both in planktonic culture and as a biofilm. Clinical strains differing in their biofilm phenotype and antibiotic resistance profile were selected to further identify possible mechanisms behind increased tolerance to isolated phages.

Keywords: Staphylococcus epidemidis; biofilms; phage safety and efficacy; prosthetic joint infections; therapeutic phages.

Figure 1

Electron micrographs of phage COP-80A (A) and phage aggregate of COP-E712 (B). Scale bar = 100 nm.

Figure 2

Antibacterial (A) and antibiofilm (B) activity of phages COP-80A, COP-80B and COP-110 against S. epidermidis COB-Sec1 (biofilm deficient) and COB-SE3 (biofilm proficient) at MOI 10. (A) Growth kinetics of COB-Sec1 and COB-SE3 in the presence of COP-80A, COP-80B and COP-110 was monitored for 24 h Results are shown as mean values of two experiments (biological replicates) with shaded area representing range of measured OD₆₀₀. (B) Mature 24-hour biofilms of COB-Sec1 and COB-SE3 were treated with phages for 24 h and changes in their structure was determined by brightfield microscopy. Single cells are indicated by black arrows and cell aggregates by white arrows.