Phage-Derived Endolysins Against Resistant Staphylococcus spp.: A Review of Features, Antibacterial Activities, and Recent Applications

[Application of phages in farm animals, food and the environment as part of a One Health approach-potentials and challenges]

In order to ensure the holistic protection of human, animal and environmental health (commonly referred to as One Health), alternatives to the available antimicrobial approaches are required. Although antibiotic drugs have an outstanding broad spectrum of activity, their use is under discussion due to increasingly occurring resistances. Furthermore, the utilisation of antibiotics can result in significant consequences for the affected microbiome, often irreversibly altering its natural composition. The necessity for the implementation of alternative and targeted control measures for bacterial pathogens (e.g. zoonoses) represents a significant challenge for all sectors within the One Health framework. With growing interest, control strategies, some of which have been neglected for centuries, are under discussion for use as valuable tool for safeguarding health across all sectors.Bacteriophages (phages) represent a naturally occurring biological resource with promising potential for use in targeted biocontrol of specific bacteria. As bacterial viruses, they interact specifically with their bacterial hosts, invading them to utilize the bacterial metabolism for their replication, finally destroying the infected bacterial cell. The benefits of this natural predator-prey relationship for the control of bacterial pathogens have long been recognized and extensively studied. This review summarises selected studies on the use of phages, illustrating the potential and application possibilities, but also the challenges of phage use. Due to their cross-sectoral relevance, the use of phages in farm animals, food and the environment is presented as an example.

Application of phage-derived enzymes for enhancing food safety

Foodborne pathogens such as Salmonella, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus present significant public health threats, causing widespread illness and economic loss. Contaminated food is responsible for an estimated 600 million illnesses and 420,000 deaths annually, with low- and middle-income countries facing losses of approximately $110 billion each year. Traditional methods to ensure food safety, including antimicrobials and preservatives, can contribute to the development of antimicrobial-resistant bacteria, highlighting the need for alternative strategies. Bacteriophages are gaining renewed attention as promising alternatives to conventional antibiotics due to their specifically target bacteria and their lower potential for causing adverse effects. However, their practical application is limited by challenges such as narrow host ranges, the emergence of phage-resistant bacteria, and stability issues. Recent research has shifted focus towards phage-derived enzymes, including endolysins, depolymerases, holins, and spanins, which are involved in the phage lytic cycle. These enzymes, as potential approaches to food safety, have demonstrated significant efficacy in targeting and lysing bacterial pathogens, making them suitable for controlling foodborne pathogens and preventing foodborne illnesses. Phage-derived enzymes also show promise in controlling biofilms and enhancing antimicrobial activity when combined with other antimicrobials. Therefore, this review emphasizes recent advancements in the use of the phage-derived enzymes for food safety, addresses their limitations, and suggests strategies to enhance their effectiveness in food processing and storage environments.

Anti-Staphylococcus aureus Activity and Structural Characterization of Rationally Designed Peptides

Background/Objectives: Microbial infections represent a significant threat to public health due to the emergence and spread of antimicrobial resistance. Adjunctive and alternative therapeutic strategies are explored to tackle this issue, including the use of natural or synthetic antimicrobial peptides. Previous research showed that antibody-derived peptides possess antimicrobial, antiviral, and immunomodulatory properties. This study aimed to characterize newly designed antibody-derived peptides and evaluate their effectiveness against representative strains of Staphylococcus aureus, including drug-resistant isolates. Methods: Colony-forming unit assays and confocal microscopy studies were performed to evaluate peptide activity against planktonic microbial cells. Cytotoxicity tests were performed on THP-1 human monocytic cells. Circular dichroism (CD) and nuclear magnetic resonance (NMR) were employed for the conformational characterization of peptides. Results: The half-maximal effective concentrations of the peptides against bacterial reference strains and drug-resistant isolates ranged from 0.17 to 18.05 µM, while cytotoxic effects were not observed against mammalian cells. A killing kinetics analysis and observation by confocal microscopy of the interaction between peptides and bacteria suggested a mechanism of action involving membrane perturbation. CD studies showed that all peptides predominantly exhibit a random coil arrangement in aqueous solution. NMR spectroscopy revealed that the most active peptide adopts a helical conformation in the presence of membrane mimetics. Conclusions: The structural characterization and evaluation of the newly designed peptides' antimicrobial activity may lead to the selection of a candidate to be further studied to develop an alternative treatment against microbial infections caused by drug-resistant strains.

Phage Endolysins as an Alternative Biocontrol Strategy for Pathogenic and Spoilage Microorganisms in the Food Industry

Food contamination by pathogenic and spoilage bacteria causes approximately 47 million cases of foodborne diseases in the United States and leads to tons of food spoilage, worsening the food loss situation worldwide. In addition, conventional preservation treatments implemented in the food industry decrease food's nutritional and organoleptic quality. Therefore, there is a need for new alternatives to counteract food contamination without altering its characteristics. Endolysins are a promising strategy due to their unique properties, such as host specificity, synergism with other antibacterial agents, mode of action, and low probability of resistance development. These characteristics differentiate them from other antibacterial agents used in the food industry. Endolysins are enzymes produced by bacteriophages during the process of bacterial infection and lysis. This review describes the advances related to endolysin application systems in food, considering their potential for food safety and an overview of the application conditions according to the type of food and bacteria to be controlled. We also highlight the need for new studies on endolysin encapsulation and prolongation of the action time in cases of outbreaks that allow obtaining key information to improve the application of endolysins in different food matrices during food processing and storage.

The Unique Capability of Endolysin to Tackle Antibiotic Resistance: Cracking the Barrier

The lack of new antibacterial medicines and the rapid rise in bacterial resistance to antibiotics pose a major threat to individuals and healthcare systems. Despite the availability of various antibiotics, bacterial resistance has emerged for almost every antibiotic discovered to date. The increasing prevalence of multidrug-resistant bacterial strains has rendered some infections nearly untreatable, posing severe challenges to health care. Thus, the development of alternatives to conventional antibiotics is critical for the treatment of both humans and food-producing animals. Endolysins, which are peptidoglycan hydrolases encoded by bacteriophages, represent a promising new class of antimicrobials. Preliminary research suggests that endolysins are more effective against Gram-positive bacteria than Gram-negative bacteria when administered exogenously, although they can still damage the cell wall of Gram-negative bacteria. Numerous endolysins have a modular domain structure that divides their binding and catalytic activity into distinct subunits, which helps maximize their bioengineering and potential drug development. Endolysins and endolysin-derived antimicrobials offer several advantages as antibiotic substitutes. They have a unique mechanism of action and efficacy against bacterial persisters (without requiring an active host metabolism); subsequently, they target both Gram-positive and Gram-negative bacteria (including antibiotic-resistant strains), and mycobacteria. Furthermore, there has been limited evidence of endolysin being resistant. Because these enzymes target highly conserved links, resistance may develop more slowly compared to traditional antibiotics. This review provides an overview and insight of the potential applications of endolysins as novel antimicrobials.