Endolysin LysSA97 is synergistic with carvacrol in controlling Staphylococcus aureus in foods

Discovery of Antimicrobial Lysins from the "Dark Matter" of Uncharacterized Phages Using Artificial Intelligence

The rapid rise of antibiotic resistance and slow discovery of new antibiotics have threatened global health. While novel phage lysins have emerged as potential antibacterial agents, experimental screening methods for novel lysins pose significant challenges due to the enormous workload. Here, the first unified software package, namely DeepLysin, is developed to employ artificial intelligence for mining the vast genome reservoirs ("dark matter") for novel antibacterial phage lysins. Putative lysins are computationally screened from uncharacterized Staphylococcus aureus phages and 17 novel lysins are randomly selected for experimental validation. Seven candidates exhibit excellent in vitro antibacterial activity, with LLysSA9 exceeding that of the best-in-class alternative. The efficacy of LLysSA9 is further demonstrated in mouse bloodstream and wound infection models. Therefore, this study demonstrates the potential of integrating computational and experimental approaches to expedite the discovery of new antibacterial proteins for combating increasing antimicrobial resistance.

Active Films of Cassava Starch Incorporated with Carvacrol Nanocapsules

The synthesis of active films with natural antimicrobials from renewable sources offers an alternative to conventional non-biodegradable packaging and synthetic additives. This study aimed to develop cassava starch films with antimicrobial activity by incorporating either free carvacrol or chia mucilage nanocapsules loaded with carvacrol (CMNC) and assess their impact on the physical, mechanical, and barrier properties of the films, as well as their efficacy against foodborne pathogens. The addition of free carvacrol led to a reduction in mechanical properties due to its hydrophobic nature and limited interaction with the polymeric matrix. Conversely, CMNC enhanced elongation at break and reduced light transmission, with a more uniform distribution in the polymeric matrix. Films containing 8% carvacrol exhibited inhibitory effects against Salmonella and Listeria monocytogenes, further potentiated when encapsulated in chia mucilage nanocapsules. These findings suggest that such films hold promise as active packaging materials to inhibit bacterial growth, ensuring food safety and extending shelf life.

Development of sensitizer peptide-fused endolysin Lys1S-L9P acting against multidrug-resistant gram-negative bacteria

The advent of multidrug-resistant (MDR) bacteria poses a major threat to public health, garnering attention to novel antibiotic replacements. Endolysin, a bacteriophage-derived cell wall-degrading enzyme, is a promising alternative to conventional antibiotics. However, it is challenging to control Gram-negative bacteria due to the presence of the outer membrane that shields the peptidoglycan layer from enzymatic degradation. To overcome this threshold, we constructed the fusion endolysin Lys1S-L9P by combining endolysin LysSPN1S with KL-L9P, a sensitizer peptide known to extend efficacy of antibiotics by perturbing the outer membrane of Gram-negative bacteria. In addition, we established a new endolysin purification procedure that increases solubility allowing a 4-fold increase in production yield of Lys1S-L9P. The sensitizer peptide-fused endolysin Lys1S-L9P exhibited high bactericidal effects against many MDR Gram-negative pathogens and was more effective in eradicating biofilms compared to LysSPN1S. Moreover, Lys1S-L9P showed potential for clinical use, maintaining stability at various storage temperatures without cytotoxicity against human cells. In the in vivo Galleria mellonella model, Lys1S-L9P demonstrated potent antibacterial activity against MDR Gram-negative bacteria without inducing any toxic activity. This study suggest that Lys1S-L9P could be a potential biocontrol agent to combat MDR Gram-negative bacteria.

Effective treatment of a broad-host-range lytic phage SapYZU15 in eliminating Staphylococcus aureus from subcutaneous infection

Multidrug resistance (MDR) Staphylococcus aureus is frequently isolated from food products, and can cause severe clinical infection. Bacteriophage (phage) therapy is a promising biocontrol agent against MDR S. aureus in food contamination and clinical infections. In this study, the antimicrobial susceptibility of 47 S. aureus isolates from three swine farms, two slaughterhouses, and four markets (Yangzhou, China) were evaluated. The biological characteristics of four lytic S. aureus phages were compared and the lytic activity of phage SapYZU15 against MDR S. aureus was assessed using milk, fresh pork and a mouse model of subcutaneous abscess. The results showed that 28 S. aureus isolates (59.6%, 28/47) exhibited multiple antibiotic resistance to at least three different classes of antibiotics. Compared to SapYZU01, SapYZU02, and SapYZU03, SapYZU15 had a shorter latent period (10 min), larger burst size (322.00 PFU/cell), broader host range, wider temperature stability (-80 to 50 °C), and pH stability. Furthermore, SapYZU15 significantly reduces the counts of S. aureus in milk and pork (5.69 and 1.16 log colony-forming unit/mL, respectively) at 25 °C and controls the growth of S. aureus at 4 °C. Compared to the mice infected with S. aureus MRSA JCSC 4744 and cocktail (S. aureus YZUsa1, YZUsa4, YZUsa12, YZUsa14, and MRSA JCSC 4744), treatment with SapYZU15 led to faster tissue healing, less weight loss, and lower viable S. aureus counts in the murine abscess model. Moreover, prevention with SapYZU15 effectively inhibited abscess formation through a synergistic effect with pro-inflammatory cytokines. Consequently, our results suggest that SapYZU15 is an effective strategy for controlling S. aureus contamination in food products, and possesses an immense potential to treat and prevent clinic infection caused by MDR S. aureus strains. The interactions and mechanisms between SapYZU15 and its bacterial host differed depending on the model, temperature, and multiplicity of infection (MOI).

Control of Escherichia coli in Fresh-Cut Mixed Vegetables Using a Combination of Bacteriophage and Carvacrol

The continual emergence of antibiotic-resistant bacteria and the slow development of new antibiotics has driven the resurgent interest in the potential application of bacteriophages as antimicrobial agents in different medical and industrial sectors. In the present study, the potential of combining phage biocontrol and a natural plant compound (carvacrol) in controlling Escherichia coli on fresh-cut mixed vegetable was evaluated. Four coliphages, designated Escherichia phage SUT_E420, Escherichia phage SUT_E520, Escherichia phage SUT_E1520 and Escherichia phage SUT_E1620, were isolated from raw sewage. Biological characterization revealed that all four phages had a latent period of 20-30 min and a burst size ranging from 116 plaque-forming units (PFU)/colony forming units (CFU) to 441 PFU/CFU. The phages effectively inhibited the growth of respective host bacteria in vitro, especially when used at a high multiplicity of infection (MOI). Based on transmission electron microscopy analysis, all phages were classified as tailed phages in the class of Caudoviricetes. Additionally, next generation sequencing indicated that none of the selected coliphages contained genes encoding virulence or antimicrobial resistance factors, highlighting the suitability of isolated phages as biocontrol agents. When a phage cocktail (~109 PFU/mL) was applied alone onto fresh-cut mixed vegetables artificially contaminated with E. coli, no bacteria were recovered from treated samples on Day 0, followed by a gradual increase in the E. coli population after 24 h of incubation at 8 °C. On the other hand, no significant differences (p < 0.05) were observed between treated and non-treated samples in terms of E. coli viable counts when carvacrol at the minimum inhibitory concentration (MIC) of 6.25 μL/mL was applied alone. When a phage cocktail at an MOI of ~1000 and MIC carvacrol were applied in combination, no E. coli were recovered from treated samples on Day 0 and 1, followed by a slight increase in the E. coli population to approximately 1.2-1.3 log CFU/mL after 48 h of incubation at 8 °C. However, total elimination of E. coli was observed in samples treated with a phage cocktail at a higher MOI of ~2000 and carvacrol at MIC, with a reduction of approximately 4 log CFU/mL observed at the end of Day 3. The results obtained in this study highlight the potential of combined treatment involving phage biocontrol and carvacrol as a new alternative method to reduce E. coli contamination in minimally processed ready-to-eat foods.

A comprehensive review of the applications of bacteriophage-derived endolysins for foodborne bacterial pathogens and food safety: recent advances, challenges, and future perspective

Foodborne diseases are caused by food contaminated by pathogenic bacteria such as Escherichia coli, Salmonella, Staphylococcus aureus, Listeria monocytogenes, Campylobacter, and Clostridium, a critical threat to human health. As a novel antibacterial agent against foodborne pathogens, endolysins are peptidoglycan hydrolases encoded by bacteriophages that lyse bacterial cells by targeting their cell wall, notably in Gram-positive bacteria due to their naturally exposed peptidoglycan layer. These lytic enzymes have gained scientists' interest in recent years due to their selectivity, mode of action, engineering potential, and lack of resistance mechanisms. The use of endolysins for food safety has undergone significant improvements, which are summarized and discussed in this review. Endolysins can remove bacterial biofilms of foodborne pathogens and their cell wall-binding domain can be employed as a tool for quick detection of foodborne pathogens. We explained the applications of endolysin for eliminating pathogenic bacteria in livestock and various food matrices, as well as the limitations and challenges in use as a dietary supplement. We also highlight the novel techniques of the development of engineering endolysin for targeting Gram-negative bacterial pathogens. In conclusion, endolysin is safe and effective against foodborne pathogens and has no adverse effect on human cells and beneficial microbiota. As a result, endolysin could be employed as a functional bio-preservative agent to improve food stability and safety and maintain the natural taste of food quality.

Phage Endolysins: Advances in the World of Food Safety

As antimicrobial resistance continues to escalate, the exploration of alternative approaches to safeguard food safety becomes more crucial than ever. Phage endolysins are enzymes derived from phages that possess the ability to break down bacterial cell walls. They have emerged as promising antibacterial agents suitable for integration into food processing systems. Their application as food preservatives can effectively regulate pathogens, thus contributing to an overall improvement in food safety. This review summarizes the latest techniques considering endolysins' potential for food safety. These techniques include native and engineered endolysins for controlling bacterial contamination at different points within the food production chain. However, we find that characterizing endolysins through in vitro methods proves to be time consuming and resource intensive. Alternatively, the emergence of advanced high-throughput sequencing technology necessitates the creation of a robust computational framework to efficiently characterize recently identified endolysins, paving the way for future research. Machine learning encompasses potent tools capable of analyzing intricate datasets and pattern recognition. This study briefly reviewed the use of these industry 4.0 technologies for advancing the research in food industry. We aimed to provide current status of endolysins in food industry and new insights by implementing these industry 4.0 strategies revolutionizes endolysin development. It will enhance food safety, customization, efficiency, transparency, and collaboration while reducing regulatory hurdles and ensuring timely product availability.

LysGR1, a novel thermostable endolysin from Geobacillus stearothermophilus bacteriophage GR1

Geobacillus stearothermophilus is a highly thermophilic, spore-forming Gram-positive bacterium that causes flat sour spoilage in low-acid canned foods. To address this problem, we isolated G. stearothermophilus-infecting phage GR1 from the soil and characterized its endolysin LysGR1. Phage GR1 belongs to the Siphoviridae family and possesses a genome of 79,387 DNA bps with 108 putative open reading frames. GR1 demonstrated a very low degree of homology to previously reported phages, indicating that it is novel. The endolysin of GR1 (LysGR1) contains an N-terminal amidase domain as an enzymatically active domain (EAD) and two C-terminal LysM domains as a cell wall binding domain (CBD). Although GR1 is specific to certain strains of G. stearothermophilus, LysGR1 showed a much broader lytic range, killing all the tested strains of G. stearothermophilus and several foodborne pathogens, such as Clostridium perfringens, Listeria monocytogenes, and Escherichia coli O157:H7. LysGR1_EAD, alone, also exhibits lytic activity against a wide range of bacteria, including Bacillus cereus, which is not terminated by a full-length endolysin. Both LysGR1 and its EAD effectively remove the G. stearothermophilus biofilms and are highly thermostable, retaining about 70% of their lytic activity after a 15-min incubation at 70°C. Considering the high thermal stability, broad lytic activity, and biofilm reduction efficacy of LysGR1 and its EAD, we hypothesize that these enzymes could act as promising biocontrol agents against G. stearothermophilus and as foodborne pathogens.

Characterization of a broad-spectrum endolysin rLysJNwz and its utility against Salmonella in foods

Salmonella is a common foodborne pathogen worldwide. The use of bacteriophage-encoded endolysins as antimicrobial agents is a promising approach for controlling pathogenic contamination. In this context, a recombinant endolysin named rLysJNwz, consisting of a single domain falling with the L-alanogyl-D-glutamate peptidase-like family, was cloned, expressed, and characterized. The yield of rLysJNwz was about 25 mg/L. Synergy between 7.5 μg/mL rLysJNwz and 0.5 mmol/L EDTA could decrease the viable counts of Salmonella NCTC 8271 by 93.28%. A synergistic effect between rLysJNwz and polymyxin B was demonstrated, exhibiting the MIC of polymyxin B decreased by twofold. Specifically, rlysJNwz had strong thermostability at temperatures (4-95 °C) and maintained high activity at pHs from 5.0 to 11.0. rlysJNwz was a metal ion-dependent peptidase, which activated by divalent metal ions such as Zn²⁺, Mn²⁺, or Ca²⁺. Moreover, it was also found that the synergism of rlysJNwz and EDTA had bactericidal activities against a broad range of Gram-negative bacteria, including several multidrug-resistant bacteria. The application of rLysJNwz combined with EDTA was evaluated on contaminated eggs and lettuce for 60 min, displaying more than 86.7% and 86.5% reduction of viable Salmonella, respectively. Hence, these results suggest that rLysJNwz is a potential antibacterial agent to control Salmonella, especially antibiotic-resistant pathogen contamination in the field of food safety. KEY POINTS: • rLysJNwz shows lytic activities against a broad range of Gram-negative bacteria. • Endolysin rLysJNwz is a stable metalloenzyme and has high thermostability. • rLysJNwz and 0.5 mmol/L EDTA synergistically inactivate Salmonella on eggs and lettuce.

Antimicrobial mechanisms of spice essential oils and application in food industry

Spice essential oils (SEOs) are commonly used in food flavoring and are considered an effective food preservative. It has a broad range of applications and promising development prospects. As a natural food additive, SEOs' antimicrobial effects have been widely studied and utilized towards food preservation. Many SEOs have exhibited significant antimicrobial activities against food-borne pathogenic and food spoilage microorganisms. We reviewed the antibacterial and antifungal properties of SEOs, the active components, their corresponding mechanisms of actions, as well as their application in the food industry, providing a theoretical basis for SEOs' further development and application as natural preservatives.

Bacteriophage and endolysin engineering for biocontrol of food pathogens/pathogens in the food: recent advances and future trends

Despite advances in modern technologies, various foodborne outbreaks have continuously threatened the food safety. The overuse of and abuse/misuse of antibiotics have escalated this threat due to the prevalence of multidrug-resistant (MDR) pathogens. Therefore, the development of new methodologies for controlling microbial contamination is extremely important to ensure the food safety. As an alternative to antibiotics, bacteriophages(phages) and derived endolysins have been proposed as novel, effective, and safe antimicrobial agents and applied for the prevention and/or eradication of bacterial contaminants even in foods and food processing facilities. In this review, we describe recent genetic and protein engineering tools for phages and endolysins. The major aim of engineering is to overcome limitations such as a narrow host range, low antimicrobial activity, and low stability of phages and endolysins. Phage engineering also aims to deter the emergence of phage resistance. In the case of endolysin engineering, enhanced antibacterial ability against Gram-negative and Gram-positive bacteria is another important goal. Here, we summarize the successful studies of phages and endolysins treatment in different types of food. Moreover, this review highlights the recent advances in engineering techniques for phages and endolysins, discusses existing challenges, and suggests technical opportunities for further development, especially in terms of antimicrobial agents in the food industry.

Synergistic inactivation of Listeria and E. coli using a combination of erythorbyl laurate and mild heating and its application in decontamination of peas as a model fresh produce

We investigated the synergistic antimicrobial activity of erythorbyl laurate (EL) and mild heating co-treatment on the Gram-positive Listeria innocua and Gram-negative Escherichia coli O157:H7 bacteria. EL (2 mM) and mild heating (55 °C for 3 min) resulted in 3.1 and 0.5 log colony forming units (CFU)/mL reductions in the number of L. innocua, respectively, compared to a 6.4 log CFU/mL reduction induced by the combined treatment of EL and mild heating in saline. EL (10 mM) and mild heating (55 °C for 3 min) resulted in 1.3 and 0.7 log CFU/mL reductions in the number of E. coli O157:H7, respectively, compared to a 6.2 log CFU/mL reduction with the combined treatment in saline. EL, a membrane-active compound, showed a strong synergistic effect with mild heating, possibly due to enhanced disruption of the bacterial cell membrane. The synergistic antibacterial effect was evaluated using inoculated English peas (Pisum sativum) and this combined treatment (2 mM EL and mild heating against L. innocua and 10 mM EL and mild heating against E. coli O157:H7) resulted in more than 7 log reductions in the numbers of L. innocua and E. coli O157:H7, inoculated on the surface of fresh peas. The treatments did not show significant difference in the color or texture of treated peas compared to the non-treated controls. This is the first report illustrating synergistic activity of EL and mild heating for both the gram positive (L. innocua) and the gram negative (E. coli O157:H7) bacteria on food. Overall, this research will illustrate the development of more effective and rapid antibacterial surface disinfection method for application in the processing of minimally processed foods.

Retroreflection-based sandwich type affinity sensing of isothermal gene amplification products for foodborne pathogen detection

Loop-mediated isothermal amplification (LAMP) is an outstanding method for molecular diagnostics, as the rapid, specific, and sensitive amplification of target genes is possible. However, it is necessary to measure fluorescence in the quantitative analysis of LAMP products, so a sophisticated optical setup is required. This study tried to develop a novel sensing method that can quantify target analytes with simple equipment, such as nonspectroscopic white light and a CMOS camera. To achieve this, a retroreflective Janus particle (RJP) as a probe and specially designed loop primers, fluorescein isothiocyanate (FITC)- and biotin-modified loop primers, were introduced into the LAMP system. By performing LAMP in the presence of designed primers, double-stranded amplicons possessing FITC and biotin labels at each end are generated in proportion to the quantity of the target pathogen. Using the anti-FITC antibody-modified sensing surface and streptavidin-conjugated RJP probes, the amplicons can be captured in sandwich-configuration and detected under nonspectroscopic conditions composed of white light and a camera. To confirm the feasibility of the sensing system, the invA gene of Salmonella was selected as the target. It was possible to quantitatively analyze the Salmonella concentration from 0 to 10⁶ colony-forming units, sufficiently covering the required detection range. In addition, quantitative analyses of pathogens in contaminated food sources, including milk and chicken meat, were successfully conducted with a limit of detection of 10 CFU.

Bactericidal and antibiofilm properties of Rumex japonicus Houtt. on multidrug-resistant Staphylococcus aureus isolated from milk

Multidrug-resistant (MDR) Staphylococcus aureus and its biofilm formation have been challenging to control in milk and dairy industries. Biofilms formed by Staph. aureus may result in the failure of antibacterial agents and disinfectants to penetrate the biofilm in an attempt to control contamination. Novel natural antibacterial agents are required to combat MDR bacteria and biofilms. In this study, we evaluated the bactericidal, antibiofilm, and antimotility effects of Rumex japonicus Houtt. (RJH) extract on MDR Staph. aureus isolated from milk. The RJH extract exhibited good antibacterial activity against MDR strains with minimum inhibitory concentrations (MIC) ranging from 0.78 to 6.25 mg/mL and minimum bactericidal concentrations ranging from 3.125 to 12.5 mg/mL. The extract showed strong inhibition of biofilm formation (81.9%) at sub-MIC value and eradication of biofilm at higher concentrations. The motility of Staph. aureus was effectively blocked by the extract. Major compounds emodin, chrysophanol, and physcion were identified in RJH extract using HPLC-linear trap quadrupole (LTQ)/Orbitrap-mass spectrometry. The extract was nontoxic to human epithelial cell lines such as Caco-2 and HT-29 cell lines at concentrations ranging from 0.1 to 0.5 mg/mL, and from 0.1 to 0.75 mg/mL, respectively. These findings suggest that RJH extract could be an alternative to synthetic preservatives in milk and dairy products.

Combining carvacrol and nisin in biodegradable films for antibacterial packaging applications

In this work, the feasibility of antibacterial biopolymeric films containing carvacrol (CRV) and a nisin commercial formulation (Nis) for potential food packaging applications was investigated. As polymer matrix, a commercial biodegradable polymer formulation of Mater-Bi (MB) was chosen due to its significant food packaging applications. CRV and Nis were chosen due to their well-established antibacterial properties and their potential synergistic effect. MB/CRV, MB/Nis, and MB/CRV/Nis systems were produced by melt mixing and compression molding. The mechanical properties of the films were evaluated by tensile tests. Differential scanning calorimetry was assessed aiming at investigating the effect of the two compounds and their mixture on the thermal properties of MB. The release profile of CRV and Nis from the MB-based films was evaluated in water at 4 °C by UV-Vis measurements and it was fitted with a power-law model. The antibacterial activity of MB-based films was tested in vitro against Listeria monocytogenes, Salmonella enteritidis, Escherichia coli, and Staphylococcus aureus. The combination of CRV and Nis strongly affected the properties of the MB-based films and ensured higher antibacterial activity if compared to MB/CRV and MB/Nis systems.

Endolysin, a Promising Solution against Antimicrobial Resistance

Antimicrobial resistance (AMR) is a global crisis for human public health which threatens the effective prevention and control of ever-increasing infectious diseases. The advent of pandrug-resistant bacteria makes most, if not all, available antibiotics invalid. Meanwhile, the pipeline of novel antibiotics development stagnates, which prompts scientists and pharmacists to develop unconventional antimicrobials. Bacteriophage-derived endolysins are cell wall hydrolases which could hydrolyze the peptidoglycan layer from within and outside of bacterial pathogens. With high specificity, rapid action, high efficiency, and low risk of resistance development, endolysins are believed to be among the best alternative therapeutic agents to treat multidrug resistant (MDR) bacteria. As of now, endolysins have been applied to diverse aspects. In this review, we comprehensively introduce the structures and activities of endolysins and summarize the latest application progress of recombinant endolysins in the fields of medical treatment, pathogen diagnosis, food safety, and agriculture.

Characterization of a novel phage depolymerase specific to Escherichia coli O157:H7 and biofilm control on abiotic surfaces

The increasing prevalence of foodborne diseases caused by Escherichia coli O157:H7 as well as its ability to form biofilms poses major threats to public health worldwide. With increasing concerns about the limitations of current disinfectant treatments, phage-derived depolymerases may be used as promising biocontrol agents. Therefore, in this study, the characterization, purification, and application of a novel phage depolymerase, Dpo10, specifically targeting the lipopolysaccharides of E. coli O157, was performed. Dpo10, with a molecular mass of 98 kDa, was predicted to possess pectate lyase activity via genome analysis and considered to act as a receptor-binding protein of the phage. We confirmed that the purified Dpo10 showed O-polysaccharide degrading activity only for the E. coli O157 strains by observing its opaque halo. Dpo10 maintained stable enzymatic activities across a wide range of temperature conditions under 55°C and mild basic pH. Notably, Dpo10 did not inhibit bacterial growth but significantly increased the complement-mediated serum lysis of E. coli O157 by degrading its O-polysaccharides. Moreover, Dpo10 inhibited the biofilm formation against E. coli O157 on abiotic polystyrene by 8-fold and stainless steel by 2.56 log CFU/coupon. This inhibition was visually confirmed via fieldemission scanning electron microscopy. Therefore, the novel depolymerase from E. coli siphophage exhibits specific binding and lytic activities on the lipopolysaccharide of E. coli O157 and may be used as a promising anti-biofilm agent against the E. coli O157:H7 strain.

Bacteriophage endolysins against gram-positive bacteria, an overview on the clinical development and recent advances on the delivery and formulation strategies

Facing the increasing threat of multi-drug antimicrobial resistance (AMR), humans strive to search for antibiotic drug candidates and antibacterial alternatives from all possible places, from soils in remote areas to deep in the sea. In this "gold rush for antibacterials," researchers turn to the natural enemy of bacterial cells, bacteriophage (phages), and find them a rich source of weapons for AMR bacteria. Endolysins (lysins), the enzymes phages use to break the bacterial cells from within, have been shown to be highly selective and efficient in killing their target bacteria from outside while maintaining a low occurrence of bacterial resistance. In this review, we start with the structures and mechanisms of action of lysins against Gram-positive (GM+) bacteria. The developmental history of lysins is also outlined. Then, we detail the latest preclinical and clinical research on their safety and efficacy against GM+ bacteria, focusing on the formulation strategies of these enzymes. Finally, the challenges and potential hurdles are discussed. Notwithstanding these limitations, the trends in development indicate that the first, approved lysin drugs will be available soon in the near future. Overall, this review presents a timely summary of the current progress on lysins as antibacterial enzymes for AMR GM+ bacteria, and provides a guidebook for biomaterial researchers who are dedicating themselves to the battle against bacterial infections.

Overview of the risks of Staphylococcus aureus infections and their control by bacteriophages and bacteriophage-encoded products

Staphylococcus aureus is the leading cause of secondary infections in hospitals and a challenging pathogen in food industries. Decades after it was first reported, β-lactam-resistant S. aureus remains a subject of intense research owing to the ever-increasing issue of drug resistance. S. aureus bacteriophages (phages) or their encoded products are considered an alternative to antibiotics as they have been shown to be effective in treating some S. aureus-associated infections. In this review, we present a concise collection of the literature on the pathogenic potential of S. aureus and examine the prospects of using S. aureus phages and their encoded products as antimicrobials.

Bacteriophage-encoded enzymes destroying bacterial cell membranes and walls, and their potential use as antimicrobial agents

Appearance of pathogenic bacteria resistant to most, if not all, known antibiotics is currently one of the most significant medical problems. Therefore, development of novel antibacterial therapies is crucial for efficient treatment of bacterial infections in the near future. One possible option is to employ enzymes, encoded by bacteriophages, which cause destruction of bacterial cell membranes and walls. Bacteriophages use such enzymes to destroy bacterial host cells at the final stage of their lytic development, in order to ensure effective liberation of progeny virions. Nevertheless, to use such bacteriophage-encoded proteins in medicine and/or biotechnology, it is crucial to understand details of their biological functions and biochemical properties. Therefore, in this review article, we will present and discuss our current knowledge on the processes of bacteriophage-mediated bacterial cell lysis, with special emphasis on enzymes involved in them. Regulation of timing of the lysis is also discussed. Finally, possibilities of the practical use of these enzymes as antibacterial agents will be underlined and perspectives of this aspect will be presented.

Synergistic effects of endolysin Lysqdvp001 and ε-poly-lysine in controlling Vibrio parahaemolyticus and its biofilms

The synergistic antibacterial effects between endolysin Lysqdvp001 and ε-poly-lysine (ε-PL) against Vibrio parahaemolyticus (V. parahaemolyticus) were investigated in this study. Lysqdvp001 combined with ε-PL exhibited a strong antibacterial synergism against V. parahaemolyticus. The combinations of Lysqdvp001 (≥60 U/mL) and ε-PL (≥0.2 mg/mL) dramatically decreased cell density of the bacterial suspensions at both 25 °C and 37 °C. Surface zeta potential increment and membrane hyperpolarization of V. parahaemolyticus were observed after treatment by ε-PL and its combination with Lysqdvp001. More β-lactamase and β-galactosidase were leaked from V. parahaemolyticus with combined treatment of Lysqdvp001 and ε-PL than from the bacteria treated with single Lysqdvp001 or ε-PL. Fluorescence and transmission electron microscope revealed that Lysqdvp001 and ε-PL synergistically induced the damage and morphological destruction of V. parahaemolyticus cells. When applying in Gadus macrocephalus, Penaeus orientalis and oyster, the two antimicrobials' cocktail allowed for 3.75, 4.16 and 2.50 log₁₀CFU/g reductions of V. parahaemolyticus, respectively. Besides, Lysqdvp001 in combination with ε-PL removed approximately 44%-68% of V. parahaemolyticus biofilms on polystyrene, glass and stainless steel surfaces. These results demonstrated that Lysqdvp001 and ε-PL might be used together for controlling V. parahaemolyticus and the bacterial biofilms in food industry.

Carvacrol exhibits rapid bactericidal activity against Streptococcus pyogenes through cell membrane damage

Streptococcus pyogenes is an important human pathogen worldwide. The identification of natural antibacterial phytochemicals has renewed interest due to the current scarcity of antibiotic development. Carvacrol is a monoterpenoid found in herbs. We evaluated carvacrol alone and combined with selected antibiotics against four strains of S. pyogenes in vitro. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of carvacrol against S. pyogenes were 125 µg/mL (0.53 mM) and 250 µg/mL (1.05 mM), respectively. Kill curve results showed that carvacrol exhibits instantaneous bactericidal activity against S. pyogenes. We also demonstrated the potential mechanism of action of carvacrol through compromising the cell membrane integrity. Carvacrol induced membrane integrity changes leading to leakage of cytoplasmic content such as lactate dehydrogenase enzymes and nucleic acids. We further confirmed dose-dependent rupturing of cells and cell deaths using transmission electron microscopy. The chequerboard assay results showed that carvacrol possesses an additive-synergistic effect with clindamycin or penicillin. Carvacrol alone, combined with clindamycin or penicillin, can be used as a safe and efficacious natural health product for managing streptococcal pharyngitis.

Development of a Novel Chimeric Endolysin, Lys109 With Enhanced Lytic Activity Against Staphylococcus aureus

As the incidence of antibiotic-resistant bacteria has become increased, phage endolysins are believed as one of the promising alternatives to antibiotics. However, the discovery of potent endolysin is still challenging because it is labor intensive and difficult to obtain a soluble form with high lytic activity. In this respect, the modular structures of Gram-positive endolysins can provide an opportunity to develop novel endolysins by domain rearrangement. In this study, a random domain swapping library of four different endolysins from phages infecting Staphylococcus aureus was constructed and screened to obtain engineered endolysins. The novel chimeric endolysin, Lys109 was selected and characterized for its staphylolytic activity. Lys109 exhibited greater bacterial cell lytic activity than its parental endolysins against staphylococcal planktonic cells and biofilms, showing highly improved activity in eliminating S. aureus from milk and on the surface of stainless steel. These results demonstrate that a novel chimeric endolysin with higher activity and solubility can be developed by random domain swapping and that this chimeric endolysin has a great potential as an antimicrobial agent.

Combination of synthetic anthelmintics and monoterpenes: Assessment of efficacy, and ultrastructural and biophysical properties of Haemonchus contortus using atomic force microscopy

The resistance of Haemonchus contortus to synthetic anthelmintics is of increasing concern; and different strategies are being evaluated to improve parasite control. The present study investigated the in vitro effects of combinations of synthetic compounds and monoterpenes. Additionally, the chemical association of the best combinations and their impact on the ultrastructural and biophysical properties of H. contortus eggs was evaluated. We assessed the efficacy of the monoterpenes, carvacrol, thymol, r-carvone, s-carvone, citral, and p-cymene and the anthelmintics, albendazole and levamisole using the egg hatch test (EHT) and the larval migration inhibition test (LMIT), respectively. The minimum effective concentrations of the monoterpenes, according to the EHT (efficacy ranging from 4.4%-11.8%) and LMIT (efficacy ranging from 5.6%-7.4%), were used in combination with different concentrations of synthetic compounds, and the IC₅₀ and synergism rate (SR) were calculated. Fourier-transform infrared spectroscopy (FTIR) was used to analyze the chemical association between the best combinations as revealed by the in vitro tests (albendazole and levamisole with r-carvone or s-carvone). Atomic force microscopy (AFM) was used to assess the ultrastructural and biophysical properties of H. contortus eggs treated with the albendazole and r-carvone combination. Among the monoterpenes, the highest efficacies were exhibited by carvacrol (IC₅₀ = 185.9 μg/mL) and thymol (IC₅₀ = 187.0 μg/mL), according to the EHT, and s-carvone and carvacrol (IC₅₀ = 1526.0 and 1785.3 μg/mL, respectively), according to the LMIT. According to the EHT, albendazole showed a slight statistically significant synergism in combination with r-carvone (SR = 3.8) and s-carvone (SR = 3.0). According to the LMIT, among the monoterpenes, r-carvone (SR = 1.7) and s-carvone (SR = 1.7) showed an increase in efficacy with levamisole; however, this was not statistically significant. The FTIR spectra of albendazole and levamisole, in association with r-carvone and s-carvone, indicated the presence of chemical interactions between the synthetic and natural molecules, contributing to the possible synergistic effects of these associations. Eggs treated with albendazole and r-carvone showed an increase in roughness and a decrease in height, suggesting that the treatment induced damage to the egg surface and an overflow of its internal contents. Overall, the combination of albendazole with r-carvone and s-carvone was efficacious against H. contortus, demonstrating a chemical association between the compounds; the significant changes in the egg ultrastructure justify this efficacy.

Antibacterial Mode of Action of the Daucus carota Essential Oil Active Compounds against Campylobacter jejuni and Efflux-Mediated Drug Resistance in Gram-Negative Bacteria

Today, an alarming rise of bacterial gastroenteritis in humans resulting from consuming Campylobacter-tainted foods is being observed. One of the solutions for mitigating this issue may be the antibacterial activity of essential oils. In the present research, we propose to study the antibacterial activity against Campylobacter and other Gram-negative bacteria of Daucus carota essential oil and its active molecules. In addition, a few chemically synthesized molecules such as (E)-methylisoeugenol, Elemicin, and eugenol were also studied. The results showed that the essential oil itself and its most active component, (E)-methylisoeugenol, exhibited bactericidal effects. Similar effects were detected using purified and chemically synthesized molecules. Also, it was observed that the Daucus carota essential oil and its active molecules affected intracellular potassium and intracellular ATP contents in Campylobacter cells. Inhibition of the membrane bound F_OF₁-ATPase was also observed. Eventually, for the first time, the efflux mechanism of active molecules of Daucus carota essential oil was also identified in gamma proteobacteria and its specific antibacterial activity against Campylobacter jejuni was associated with the lack of this efflux mechanism in this species.

Ameliorative Effects of Phytochemical Ingestion on Viral Infection in Honey Bees

Simple Summary

Virus infection is among the many stressors honey bees are experiencing in the modern agricultural landscape. Although some promising treatments are currently under development, no reliable cure currently exists. Here, we investigated the effects of various phytochemicals (plant-produced chemical compounds) on the survivorship of virus infected honey bees. Our results showed that, when consumed at natural concentrations like those found in flowers, caffeine is capable of significantly reducing the mortality of infected bees. It is important to note that caffeine did not clear the infected bees of all viruses and should, therefore, not be considered a virus cure. Rather, caffeine represents a potential antiviral therapeutic agent that should be studied further to improve understanding of virus-phytochemical interactions.

Abstract

Honey bee viruses are capable of causing a wide variety of devastating effects, but effective treatments have yet to be discovered. Phytochemicals represent a broad range of substances that honey bees frequently encounter and consume, many of which have been shown to improve honey bee health. However, their effect on bee viruses is largely unknown. Here, we tested the therapeutic effectiveness of carvacrol, thymol, p-coumaric acid, quercetin, and caffeine on viral infection by measuring their ability to improve survivorship in honey bees inoculated with Israeli acute paralysis virus (IAPV) using high-throughput cage bioassays. Among these candidates, caffeine was the only phytochemical capable of significantly improving survivorship, with initial screening showing that naturally occurring concentrations of caffeine (25 ppm) were sufficient to produce an ameliorative effect on IAPV infection. Consequently, we measured the scope of caffeine effectiveness in bees inoculated and uninoculated with IAPV by performing the same type of high-throughput bioassay across a wider range of caffeine concentrations. Our results indicate that caffeine may provide benefits that scale with concentration, though the exact mechanism by which caffeine ingestion improves survivorship remains uncertain. Caffeine therefore has the potential to act as an accessible and inexpensive method of treating viral infections, while also serving as a tool to further understanding of honey bee–virus interactions at a physiological and molecular level.

Combined Application of Bacteriophages and Carvacrol in the Control of Pseudomonas syringae pv. actinidiae Planktonic and Biofilm Forms

Pseudomonas syringae pv. actinidiae (Psa) is the causative agent of the bacterial canker of kiwifruit (Actinidia spp.). Phage therapy has been suggested as a viable alternative approach to controlling this disease, but its efficacy is limited by the emergence of phage-resistant mutants. Carvacrol is an essential oil that may be useful for the control of Psa. Combination therapies can be used to overcome resistance development. Here, the combination of phages (single phage suspensions of phages PN05 and PN09, and a cocktail of both phages) and carvacrol was investigated in controlling Psa planktonic and biofilm forms in vitro. The phage therapy alone (with phages PN05 and PN09), and the carvacrol alone (minimum inhibitory concentration 2.0 mg/mL), inhibited Psa growth, but the combined effect of both therapies was more effective. The phages alone effectively inhibited Psa growth for 24 h, but Psa regrowth was observed after this time. The carvacrol (2.0 mg/mL) alone prevented the biofilm formation for 48 h, but did not destroy the pre-formed biofilms. The combined treatment, phages and carvacrol (2.0 mg/mL), showed a higher efficacy, preventing Psa regrowth for more than 40 h. In conclusion, the combined treatment with phages and carvacrol may be a promising, environment-friendly and cost-effective approach to controlling Psa in the kiwifruit industry.

Bacteriophage-Derived Endolysins Applied as Potent Biocontrol Agents to Enhance Food Safety

Endolysins, bacteriophage-encoded enzymes, have emerged as antibacterial agents that can be actively applied in food processing systems as food preservatives to control pathogens and ultimately enhance food safety. Endolysins break down bacterial peptidoglycan structures at the terminal step of the phage reproduction cycle to enable phage progeny release. In particular, endolysin treatment is a novel strategy for controlling antibiotic-resistant bacteria, which are a severe and increasingly frequent problem in the food industry. In addition, endolysins can eliminate biofilms on the surfaces of utensils. Furthermore, the cell wall-binding domain of endolysins can be used as a tool for rapidly detecting pathogens. Research to extend the use of endolysins toward Gram-negative bacteria is now being extensively conducted. This review summarizes the trends in endolysin research to date and discusses the future applications of these enzymes as novel food preservation tools in the field of food safety.

Identification and in vitro Characterization of a Novel Phage Endolysin that Targets Gram-Negative Bacteria

Most double-stranded (ds) DNA phages utilize holin proteins to secrete endolysin for host peptidoglycan lysis. In contrast, several holin-independent endolysins with secretion sequences or signal-arrest-release (SAR) sequences are secreted via the Sec pathway. In this study, we characterized a novel lysis protein (M4Lys) encoded by the dsDNA phage BSPM4, whose lysis function is not dependent on either holin or the Sec pathway in vitro. In silico analysis of M4Lys revealed that it contains a putative virion protein domain and an unusual C-terminal transmembrane domain (TMD). Turbidity reduction assays and liquid chromatography-mass spectrometry using purified peptidoglycan showed that the virion protein domain of M4Lys has peptidoglycan lysis activity. In vitro overproduction of M4Lys in Escherichia coli revealed that M4Lys alone caused rapid cell lysis. Treatment of E. coli with a Sec inhibitor did not inhibit the lysis activity of M4Lys, indicating that the Sec pathway is not involved in M4Lys-mediated cell lysis. Truncation of the TMD eliminated the cell lysis phenomenon, while production of the TMD alone did not induce the cell lysis. All these findings demonstrate that M4Lys is a novel endolysin that has a unique mosaic structure distinct from other canonical endolysins and the TMD plays a critical role in M4Lys-mediated in vitro cell lysis.

Phage Lytic Protein LysRODI Prevents Staphylococcal Mastitis in Mice

Phage lytic proteins are promising antimicrobials that could complement conventional antibiotics and help to combat multi-drug resistant bacteria that cause important human and animal infections. Here, we report the characterization of endolysin LysRODI (encoded by staphylophage phiIPLA-RODI) and its application as a prophylactic mastitis treatment. The main properties of LysRODI were compared with those of endolysin LysA72 (encoded by staphylophage phiIPLA35) and the chimeric protein CHAPSH3b (derived from the virion-associated peptidoglycan hydrolase HydH5 and lysostaphin). Time-kill experiments performed with Staphylococcus aureus and Staphylococcus epidermidis demonstrated that the killing rate of LysRODI and CHAPSH3b is higher than that of LysA72 (0.1 μM protein removed 10⁷ CFU/ml of S. aureus in 30 min). Of note, all proteins failed to select resistant mutants as bacterial exposure to sub-lethal concentrations of the proteins did not alter the MIC values. Additionally, LysRODI and CHAPSH3b were non-toxic in a zebrafish embryo model at concentrations near the MIC (0.5 and 0.7 μM, respectively). Moreover, these two proteins significantly reduced mortality in a zebrafish model of systemic infection. In contrast to LysRODI, the efficacy of CHAPSH3b was dose-dependent in zebrafish, requiring higher-dose treatments to achieve the maximum survival rate. For this reason, LysRODI was selected for further analysis in mice, demonstrating great efficacy to prevent mammary infections by S. aureus and S. epidermidis. Our findings strongly support the use of phage lytic proteins as a new strategy to prevent staphylococcal mastitis.

Chitosan And N, N, N-Trimethyl Chitosan Nanoparticle Encapsulation Of Ocimum Gratissimum Essential Oil: Optimised Synthesis, In Vitro Release And Bioactivity

Background

The encapsulation of plant essential oils (EOs) with polymeric materials (e.g. chitosan (CS) and N, N, N-trimethyl chitosan (TMC)) and the further reduction of the polymers into their nano sizes are gaining research interest in nanotechnology due to potential applications in medical drug delivery systems as well as the food and pharmaceutical industry. The present study reports a novel approach for the synthesis of Ocimum gratissimum essential oil (OGEO)-loaded CS and TMC nanoparticles with distinct bioactive and physiochemical properties.

Methods

The OGEO-loaded CS and TMC nanoparticles were characterised using various microscopic and spectroscopic techniques. The bioactive compounds in Ocimum gratissimum methanolic extract (OG-MeOH) and EOs was evinced with gas chromatography-mass spectrometry (GC-MS). Total phenolic content (TPC) of OGEO and OG-MeOH was determined using the Folin-Ciocalteu method. The in vitro drug release kinetic pattern was ascertained by membrane dialysis, while antioxidant activity was determined by the 2,2-diphenyl-1picrylhydrozyl (DPPH) free radical scavenging method. The disc diffusion method was used for antibacterial activity evaluation, while MTT and a trypan blue dye exclusion assay were used to assess cytotoxic activity on MDA-MB-231 breast cancer cells.

Results

GC-MS analysis revealed components that have not been previously reported for Ocimum gratissimum. The maximum OGEO cumulative drug release percentage in vitro was observed at pH 3 for both OGEO-loaded chitosan nanoparticles (OGEO-CSNPs) and OGEO-loaded N, N, N-trimethyl chitosan nanoparticles (OGEO-TMCNPs). The antioxidant activity of OGEO-CSNPs and OGEO-TMCNPs never reached a steady state after 75 h. OGEO-TMCNPs exhibited antibacterial activity at a lower concentration for both Gram-negative and Gram-positive food pathogens. In vitro cytotoxicity revealed the increased toxicity of OGEO-TMCNPs on MDA-MB-231 breast cancer cell lines.

Conclusion

OGEO-loaded CS and TMC nanoparticles were synthesised using a novel material optimisation approach. The synthesised nanoparticles have shown a promising application in the pharmaceutical and food industries.

The Capsule Depolymerase Dpo48 Rescues Galleria mellonella and Mice From Acinetobacter baumannii Systemic Infections

The emergence of multidrug- and extensively drug-resistant Acinetobacter baumannii has made it difficult to treat and control infections caused by this bacterium. Thus, alternatives to conventional antibiotics for management of severe A. baumannii infections is urgently needed. In our previous study, we found that a capsule depolymerase Dpo48 could strip bacterial capsules, and the non-capsuled A. baumannii were significantly decreased in the presence of serum complement in vitro. Here, we further explored its potential as a therapeutic agent for controlling systemic infections caused by extensively drug-resistant A. baumannii. Prior to mammalian studies, the anti-virulence efficacy of Dpo48 was first tested in a Galleria mellonella infection model. Survival rate of Dpo48-pretreated bacteria or Dpo48 treatment group was significantly increased compared to the infective G. mellonella without treatment. Furthermore, the safety and therapeutic efficacy of Dpo48 to mice were evaluated. The mice treated with Dpo48 displayed normal serum levels of TBIL, AST, ALT, ALP, Cr, BUN and LDH, while no significant histopathology changes were observed in tissues of liver, spleen, lung, and kidney. Treatment with Dpo48 could rescue normal and immunocompromised mice from lethal peritoneal sepsis, with the bacterial counts in blood, liver, spleen, lung, and kidney significantly reduced by 1.4-3.3 log colony-forming units at 4 h posttreatment. Besides, the hemolysis and cytotoxicity assays showed that Dpo48 was non-homolytic to human red blood cells and non-toxic to human lung, liver and kidney cell lines. Overall, the present study demonstrated the promising potential of capsule depolymerases as therapeutic agents to prevent antibiotic-resistant A. baumannii infections.

Role of Bacteriophages in the Implementation of a Sustainable Dairy Chain

The growing human population is currently facing an unprecedented challenge regarding global food sustainability. Thus, it is of paramount to maintain food production and quality while avoiding a negative impact on climate change and the environment at large. Along the food chain, several practices could compromise future food safety and human health. One example is the widespread use of antibiotics and disinfectants in dairy production, which has contributed to the current antibiotic resistance crisis. Moreover, the uncontrolled release of antimicrobials to the environment poses a significant threat to natural ecosystems. For these reasons, research has recently focused on exploiting natural antimicrobials with the goal of achieving a safer and more sustainable dairy production chain. In this context, bacteriophages, viruses that infect bacteria, may become good allies to prevent and treat diseases in cattle, or be used as disinfectants in dairy facilities and as preservatives in dairy products. This review provides an overview of the current research regarding the use of phages as a global approach to reduce economic losses and food waste, while increasing food safety and reducing the environmental impact of food production. Our current understanding of progress, solutions, and future challenges in dairy production, processing, safety, waste processing, and quality assurance is also discussed.

Identification and characterization of capsule depolymerase Dpo48 from Acinetobacter baumannii phage IME200

Background

The emergence of multidrug- or extensively drug-resistant Acinetobacter baumannii has made it difficult to treat and control infections caused by this bacterium. It is urgently necessary to search for alternatives to conventional antibiotics for control of severe A. baumannii infections. In recent years, bacteriophages and their derivatives, such as depolymerases, showed great potential as antibacterial or antivirulence agents against bacterial infections. Nonetheless, unlike broad-spectrum bactericidal antibiotics, phage-encoded depolymerase targets only a limited number of bacterial strains. Therefore, identification of novel depolymerases and evaluation of their ability to control A. baumannii infections is important.

Methods

A bacteriophage was isolated from hospital sewage using an extensively drug-resistant A. baumannii strain as the host bacterium, and the phage’s plaque morphology and genomic composition were studied. A polysaccharide depolymerase (Dpo48) was expressed and identified, and the effects of pH and temperature on its activity were determined. Besides, a serum killing assay was conducted, and amino acid sequences homologous to those of putative polysaccharide depolymerases were compared.

Results

Phage IME200 yielded clear plaques surrounded by enlarged halos, with polysaccharide depolymerase activity against the host bacterium. A tail fiber protein with a Pectate_lyase_3 domain was identified as Dpo48 and characterized . Dpo48 was found to degrade the capsule polysaccharide of the bacterial surface, as revealed by Alcian blue staining. Dpo48 manifested stable activity over a broad range of pH (5.0–9.0) and temperatures (20–70 °C). Results from in vitro serum killing assays indicated that 50% serum was sufficient to cause a five log reduction of overnight enzyme-treated bacteria, with serum complement playing an important role in these killing assays. Moreover, Dpo48 had a spectrum of activity exactly the same as its parental phage IME200, which was active against 10 out of 41 A. baumannii strains. Amino acid sequence alignment showed that the putative tail fiber proteins had a relatively short, highly conserved domain in their N-terminal sequences, but their amino acid sequences containing pectate lyase domains, found in the C-terminal regions, were highly diverse.

Conclusions

Phage-encoded capsule depolymerases may become promising antivirulence agents for preventing and controlling A. baumannii infections.

Bacteriophages in Food Applications: From Foe to Friend

Bacteriophages (phages) have traditionally been considered troublesome in food fermentations, as they are an important cause of starter-culture failure and trigger significant financial losses. In addition, from an evolutionary perspective, phages have contributed to the pathogenicity of many bacteria through transduction of virulence genes. In contrast, phages have played an important positive role in molecular biology. Moreover, these agents are increasingly being recognized as a potential solution to the detection and biocontrol of various undesirable bacteria, which cause either spoilage of food materials, decreased microbiological safety of foods, or infectious diseases in food animals and crops. The documented successful applications of phages and various phage-derived molecules are discussed in this review, as are many promising new uses that are currently under development.

The Auxiliary Role of the Amidase Domain in Cell Wall Binding and Exolytic Activity of Staphylococcal Phage Endolysins

In response to increasing concern over antibiotic-resistant Staphylococcus aureus, the development of novel antimicrobials has been called for, with bacteriophage endolysins having received considerable attention as alternatives to antibiotics. Most staphylococcal phage endolysins have a modular structure consisting of an N-terminal cysteine, histidine-dependent amidohydrolases/peptidase domain (CHAP), a central amidase domain, and a C-terminal cell wall binding domain (CBD). Despite extensive studies using truncated staphylococcal endolysins, the precise function of the amidase domain has not been determined. Here, a functional analysis of each domain of two S. aureus phage endolysins (LysSA12 and LysSA97) revealed that the CHAP domain conferred the main catalytic activity, while the central amidase domain showed no enzymatic activity in degrading the intact S. aureus cell wall. However, the amidase-lacking endolysins had reduced hydrolytic activity compared to the full-length endolysins. Comparison of the binding affinities of fusion proteins consisting of the green fluorescent protein (GFP) with CBD and GFP with the amidase domain and CBD revealed that the major function of the amidase domain was to enhance the binding affinity of CBD, resulting in higher lytic activity of endolysin. These results suggest an auxiliary binding role of the amidase domain of staphylococcal endolysins, which can be useful information for designing effective antimicrobial and diagnostic agents against S. aureus.

Enhancing Whole Phage Therapy and Their Derived Antimicrobial Enzymes through Complex Formulation

The resurgence of research into phage biology and therapy is, in part, due to the increasing need for novel agents to treat multidrug-resistant infections. Despite a long clinical history in Eastern Europe and initial success within the food industry, commercialized phage products have yet to enter other sectors. This relative lack of success is, in part, due to the inherent biological limitations of whole phages. These include (but are not limited to) reaching target sites at sufficiently high concentrations to establish an infection which produces enough progeny phages to reduce the bacterial population in a clinically meaningful manner and the limited host range of some phages. Conversely, parallels can be drawn between antimicrobial enzymes derived from phages and conventional antibiotics. In the current article the biological limitations of whole phage-based therapeutics and their derived antimicrobial enzymes will be discussed. In addition, the ability of more complex formulations to address these issues, in the context of medical and non-medical applications, will also be included.

Potential for Bacteriophage Endolysins to Supplement or Replace Antibiotics in Food Production and Clinical Care

There is growing concern about the emergence of bacterial strains showing resistance to all classes of antibiotics commonly used in human medicine. Despite the broad range of available antibiotics, bacterial resistance has been identified for every antimicrobial drug developed to date. Alarmingly, there is also an increasing prevalence of multidrug-resistant bacterial strains, rendering some patients effectively untreatable. Therefore, there is an urgent need to develop alternatives to conventional antibiotics for use in the treatment of both humans and food-producing animals. Bacteriophage-encoded lytic enzymes (endolysins), which degrade the cell wall of the bacterial host to release progeny virions, are potential alternatives to antibiotics. Preliminary studies show that endolysins can disrupt the cell wall when applied exogenously, though this has so far proven more effective in Gram-positive bacteria compared with Gram-negative bacteria. Their potential for development is furthered by the prospect of bioengineering, and aided by the modular domain structure of many endolysins, which separates the binding and catalytic activities into distinct subunits. These subunits can be rearranged to create novel, chimeric enzymes with optimized functionality. Furthermore, there is evidence that the development of resistance to these enzymes may be more difficult compared with conventional antibiotics due to their targeting of highly conserved bonds.

Are Phage Lytic Proteins the Secret Weapon To Kill Staphylococcus aureus?

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most threatening microorganisms for global human health. The current strategies to reduce the impact of S. aureus include a restrictive control of worldwide antibiotic use, prophylactic measures to hinder contamination, and the search for novel antimicrobials to treat human and animal infections caused by this bacterium. The last strategy is currently the focus of considerable research. In this regard, phage lytic proteins (endolysins and virion-associated peptidoglycan hydrolases [VAPGHs]) have been proposed as suitable candidates. Indeed, these proteins display narrow-spectrum antimicrobial activity and a virtual lack of bacterial-resistance development. Additionally, the therapeutic use of phage lytic proteins in S. aureus animal infection models is yielding promising results, showing good efficacy without apparent side effects. Nonetheless, human clinical trials are still in progress, and data are not available yet. This minireview also analyzes the main obstacles for introducing phage lytic proteins as human therapeutics against S. aureus infections. Besides the common technological problems derived from large-scale production of therapeutic proteins, a major setback is the lack of a proper legal framework regulating their use. In that sense, the relevant health authorities should urgently have a timely discussion about these new antimicrobials. On the other hand, the research community should provide data to dispel any doubts regarding their efficacy and safety. Overall, the appropriate scientific data and regulatory framework will encourage pharmaceutical companies to invest in these promising antimicrobials.

Green synthesis of antimicrobial and antitumor N,N,N-trimethyl chitosan chloride/poly (acrylic acid)/silver nanocomposites

The present study is imported to solve two critical problems we face in our daily life which are microbial pollution and colon cancer. One pot green synthesis of a water soluble polyelectrolyte complex (PEC) between cationic polysaccharide as N,N,N-trimethyl chitosan chloride (TMC) and anionic polymer as poly (acrylic acid) (PAA) in presence of silver nanoparticles to yield (TMC/PAA/Ag) nanocomposites with different Ag weight ratios. Structure of TMC, PAA and TMC/PAA (PEC) were proved via different analysis tools. TMC/PAA and its Ag nanocomposites are used as antimicrobial agents against different pathogenic bacteria and fungi to solve microbial pollution. TMC/PAA-Silver nanocomposites had the highest antimicrobial activity which increases with increasing Ag %. Cytotoxicity data confirmed also that TMC/PAA/Ag (3%) had the most cytotoxic effect (the less cell viability %) towards colon cancer. TMC/PAA (PEC) was formed through electrostatic interactions between N-quaternized (-N⁺R₃) groups in TMC and carboxylate (-COO^-) groups in PAA.