Rapid bacteriolysis of Staphylococcus aureus by lysin exebacase

Lysins (peptidoglycan hydrolases) are promising new protein-based antimicrobial candidates under development to address rising antibiotic resistance encountered among pathogenic bacteria. Exebacase is an antistaphylococcal lysin and the first member of the lysin class to have entered clinical trials in the United States. In this study, the bacteriolytic activity of exebacase was characterized with time-kill assays, turbidity reduction assays, and microscopy. Three methicillin-susceptible Staphylococcus aureus and three methicillin-resistant S. aureus isolates were tested in time-kill assays over a range of concentrations from 0.25 to 8 x MIC. Exebacase demonstrated a concentration-dependent killing and showed bactericidal activity (>= 3 log(10) kill achieved relative to the starting inoculum) within 3 h at 1 x MIC against all strains tested. Dose-dependent lysis by exebacase was, furthermore, observed in the turbidity reduction assay, wherein decreases in initial OD600 of 50% were observed within similar to 15 min at concentrations as low as 4 mu g/mL. Membrane dissolution, loss of cytoplasmic material, and lysis were confirmed by video and electron microscopy. The demonstrated rapid bacteriolytic effect of exebacase is an important distinguishing feature of this novel modality. IMPORTANCE To guide the development of an investigational new antibacterial entity, microbiological data are required to evaluate the killing kinetics against target organism(s). Exebacase is a lysin (peptidoglycan hydrolase) that represents a novel antimicrobial modality based on degradation of the cell wall of Staphylococcus aureus. Killing by exebacase was determined in multiple assay formats including time-kill assays, wherein reductions of viability of >= 3 log(10) colony-forming units/mL were observed within 3 h for multiple different isolates tested, consistent with very rapid bactericidal activity. Rapid reductions in optical density were likewise observed in exebacase-treated cultures, which were visually consistent with microscopic observations of rapid lysis. Overall, exebacase provides a novel antimicrobial modality against S. aureus, characterized by a rapid cidal and lytic activity.

Automated summary

Lysins are new protein-based antimicrobial candidates used to combat antibiotic resistance. The study evaluated the bacteriolytic activity of the antistaphylococcal lysin Exebacase, showing concentration-dependent killing against Staphylococcus aureus strains. Exebacase demonstrated rapid bactericidal activity within 3 h and dose-dependent lysis at low concentrations. Microscopy confirmed membrane dissolution and cell lysis. The novel modality of Exebacase provides a rapid and effective antimicrobial solution against S. aureus.