Activity of Exebacase (CF-301) against Biofilms Formed by Staphylococcus epidermidis Strains Isolated from Prosthetic Joint Infections

Abstract

Staphylococcus epidermidis is one of the main pathogens responsible for bone and joint infections, especially those involving prosthetic materials, due to its ability to form biofilms. In these cases, biofilm formation, combined with increased antimicrobial resistance, often results in therapeutic failures. In this context, the development of innovative therapies active against S. epidermidis is a priority. The aim of this study was to evaluate the in vitro activity of the lysin exebacase (CF-301) against biofilms formed by 19 S. epidermidis clinical strains isolated from prosthetic joint infections (PJI). We determined the biomass and the remaining viable bacteria inside biofilms after 24 h of exposure to exebacase. Exebacase activity was compared to that of rifampicin, vancomycin, and daptomycin. The use of exebacase in addition to antibiotics was also assessed. Exebacase displayed (i) a significant anti-biomass activity on S. epidermidis biofilms at concentrations ≥5 mg/L (mean decrease up to 66% at 150 mg/L), (ii) significant bactericidal activity on biofilms at concentrations ≥50 mg/L (mean decrease up to 1.7 log CFU at 150 mg/L), (iii) synergistic effects when used in addition to rifampicin, vancomycin, or daptomycin. The extent of these activities varied by isolate. Exebacase can be considered a promising therapy in addition to rifampicin, vancomycin, or daptomycin in the context of PJI. Further in vitro studies are needed to understand its mechanism of action on S. epidermidis biofilms and in vivo investigations are required to confirm these data.

Keywords: CF-301; Staphylococcus epidermidis; biofilms; exebacase; prosthetic joint infections.

FIG 1

Exebacase activity in comparison to antibiotics against S. epidermidis biofilms from 19 isolates. a) Bactericidal activity: reduction of bacterial population within the preformed biofilms after 24 h of exebacase treatment at 0.05, 0.5, 5, 50, and 150 mg/L, or rifampicin at 0.01, 0.1, and 1 mg/L, vancomycin at 0.1, 1, and 10 mg/L, and daptomycin at 0.1, 1, and 10 mg/L, evaluated by enumeration of colonies on Columbia blood agar plates after serial dilutions. b) Anti-biomass activity: ratio of remaining biomass after 24 h of exebacase exposure at 0.05, 0.5, 5, 50, and 150 mg/L, rifampicin at 1 mg/L, vancomycin 10 mg/L, or daptomycin 10 mg/L, on the remaining biomass of the condition without exposition, evaluated by crystal violet staining. *, P < 0.05; **, P < 0.01; ***, P < 0.001; A: activity compared to no treatment (P < 0.05); AA: activity compared to no treatment (P < 0.01); AAA: activity compared to no treatment (P < 0.001); ¹ the 5 rifampicin-resistant isolates were excluded.

FIG 2

Anti-biofilm activity of exebacase in addition to antibiotics compared to exebacase and antibiotics alone against S. epidermidis biofilms from 19 isolates. Reduction of living bacteria inside the biofilms after 24 h of exebacase exposure at 5, 50, and 150 mg/L, and/or rifampicin at 1 mg/L, vancomycin at 10 mg/L, and daptomycin at 10 mg/L, evaluated by enumeration of colonies on Columbia blood agar plates after serial dilutions. *, P < 0.05; **, P < 0.01; ***, P < 0.001; S: synergy P < 0.05; SS: synergy P < 0.01; SSS: synergy P < 0.001, ¹ the 5 rifampicin-resistant isolates were excluded.

FIG 3

Anti-biomass activity of exebacase in addition to antbiotics compared to exebacase and antibiotics alone against S. epidermidis biofilms from 19 isolates. Remaining biomass after 24 h of exebacase exposure at 5, 50, and 150 mg/L, and/or rifampicin at 1 mg/L, vancomycin at 10 mg/L, and daptomycin 10 mg/L, evaluated by crystal violet staining. *, P < 0.05; **, P < 0.01; ***, P < 0.001; S: synergy P < 0.05; SS: synergy P < 0.01; SSS: synergy P < 0.001, ¹ the 5 rifampicin-resistant isolates were excluded.