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

Bacteriophage as a potential biotherapeutics to combat present-day crisis of multi-drug resistant pathogens

The rise of Multi-Drug Resistant (MDR) bacterial pathogens to most, if not all, currently available antibacterial agents has become a global threat. As a consequence of the antibiotic resistance epidemic, phage therapy has emerged as a potential alternative to conventional antibiotics. Despite the high therapeutic advantages of phage therapy, they have not yet been successfully used in the clinic due to various limitations of narrow host specificity compared to antibiotics, poor adhesion on biofilm surface, and susceptibility to both human and bacterial defences. This review focuses on the antibacterial effect of bacteriophage and their recent clinical trials with a special emphasis on the underlying mechanism of lytic phage action with the help of endolysin and holin. Furthermore, recent clinical trials of natural and modified endolysins and some marketed products have also been emphasized with future prospective.

The Engineered Lysin CF-370 Is Active Against Antibiotic-Resistant Gram-Negative Pathogens In Vitro and Synergizes With Meropenem in Experimental Pseudomonas aeruginosa Pneumonia

BACKGROUND

Lysins (cell wall hydrolases) targeting gram-negative organisms require engineering to permeabilize the outer membrane and access subjacent peptidoglycan to facilitate killing. In the current study, the potential clinical utility for the engineered lysin CF-370 was examined in vitro and in vivo against gram-negative pathogens important in human infections.

METHODS

Minimum inhibitory concentration (MICs) and bactericidal activity were determined using standard methods. An in vivo proof-of-concept efficacy study was conducted using a rabbit acute pneumonia model caused by Pseudomonas aeruginosa.

RESULTS

CF-370 exhibited potent antimicrobial activity, with MIC50/90 values (in µg/mL) for: P aeruginosa, 1/2; Acinetobacter baumannii, 1/1; Escherichia coli, 0.25/1; Klebsiella pneumoniae, 2/4; Enterobacter cloacae 1/4; and Stenotrophomonas maltophilia 2/8. CF-370 furthermore demonstrated bactericidal activity, activity in serum, a low propensity for resistance, anti-biofilm activity, and synergy with antibiotics. In the pneumonia model, CF-370 alone decreased bacterial densities in lungs, kidneys, and spleen versus vehicle control, and demonstrated significantly increased efficacy when combined with meropenem (vs either agent alone).

CONCLUSIONS

CF-370 is the first engineered lysin described with potent broad-spectrum in vitro activity against multiple clinically relevant gram-negative pathogens, as well as potent in vivo efficacy in an animal model of severe invasive multisystem infection.

A Review of Phage Therapy for Bone and Joint Infections

There is a strong rationale for using phages in patients with bone and joint infections (BJIs). Indeed, specific phages can infect and replicate in bacterial pathogens and have also demonstrated their activity in vitro against biofilm produced by different bacteria. However, there is a high variability of the different clinical forms of BJI, and their management is complex and frequently includes surgery followed by the administration of antibiotics. Regardless of the availability of active phages, optimal ways of phage administration in patients with BJIs are unknown. Otherwise, all BJIs are not relevant for phage therapy. Except for diabetic foot infection, a BJI with bone exposure is potentially not a relevant indication for phage therapy. On the counterpart, prosthetic joint infections in patients for whom a multidisciplinary expert team judges a conservative approach as the best option to keep the patient's function seem to be a relevant indication with the hypothesis that phage therapy could increase the rate of infection control. The ESCMID Study Group for Non-traditional Antibacterial Therapy (ESGNTA) was created in 2022. One century after the first use of phages as a therapy, the phage therapy 2.0 era, with the possibility to evaluate personalized phage therapy in modern medicine and orthopedic surgery, is just open.

In vitro activity of exebacase against methicillin-resistant Staphylococcus aureus biofilms on orthopedic Kirschner wires

Orthopedic foreign body-associated infection can be difficult to treat due to the formation of biofilms protecting microorganisms from both antimicrobials and the immune system. Exebacase is an antistaphylococcal lysin (cell wall hydrolase) under consideration for local treatment for biofilm-based infections caused by methicillin-resistant Staphylococcus aureus (MRSA). To determine the activity of exebacase, we formed MRSA biofilms on orthopedic Kirschner wires and exposed them to varying concentrations (0.098, 0.98, 9.8 mg/ml) of exebacase and/or daptomycin over 24 h. The biofilm consisted of 5.49 log10 colony forming units (cfu)/K-wire prior to treatment and remained steady throughout the experiment. Exebacase showed significant biofilm reduction at all timepoints (up to 5.78 log10 cfu/K-wire; P < 0.0495) compared to the controls at all concentrations and all time points with bactericidal activity (> 3 log10 cfu/K-wire reduction) observed for up to 12 h for the 0.098 and 0.98 mg/ml concentrations and at 24 h for 9.8 mg/ml. Daptomycin showed significant biofilm reduction, although non-bactericidal, at all time points for 0.98 and 9.8 mg/ml and at 4 and 8 h with 0.098 mg/ml (P < 0.0495). This study supports further evaluation of local administration of exebacase as a potential treatment for orthopedic implant infections.

The Lysin Exebacase Has a Low Propensity for Resistance Development in Staphylococcus aureus and Suppresses the Emergence of Resistance to Antistaphylococcal Antibiotics

Exebacase (CF-301) belongs to a novel class of protein-based antibacterial agents, called lysins (peptidoglycan hydrolases). Exebacase exhibits potent antistaphylococcal activity and is the first lysin to initiate clinical trials in the United States. To support clinical development, the potential for resistance development to exebacase was assessed over 28 days of serial daily subculture in the presence of increasing concentrations of the lysin performed in its reference broth medium. Exebacase MICs remained unchanged over serial subculture for three replicates each of methicillin-susceptible Staphylococcus aureus (MSSA) strain ATCC 29213 and methicillin-resistant S. aureus (MRSA) strain MW2. For comparator antibiotics also tested, oxacillin MICs increased by 32-fold with ATCC 29213 and daptomycin and vancomycin MICs increased by 16- and 8-fold, respectively, with MW2. Serial passage was also used to examine the capacity of exebacase to suppress selection for increased oxacillin, daptomycin, and vancomycin MICs when used together in combination, wherein daily exposures to increasing concentrations of antibiotic were performed over 28 days with the added presence of fixed sub-MIC amounts of exebacase. Exebacase suppressed increases in antibiotic MICs over this period. These findings are consistent with a low propensity for resistance to exebacase and an added benefit of reducing the potential for development of antibiotic resistance. IMPORTANCE To guide development of an investigational new antibacterial drug, microbiological data are required to understand the potential for development of resistance to the drug in the 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. Exebacase resistance was examined here using an in vitro serial passage method that assesses the impact of daily exposures to increasing concentrations of exebacase over 28 days in medium approved for use in exebacase antimicrobial susceptibility testing (AST) by the Clinical and Laboratory Standards Institute (CLSI). No changes in susceptibility to exebacase were observed over the 28-day period for multiple replicates of two S. aureus strains, indicating a low propensity for resistance development. Interestingly, while high-level resistance to commonly used antistaphylococcal antibiotics was readily obtained using the same method, the added presence of exebacase acted to suppress antibiotic resistance development.