Decontamination of Escherichia coli O157:H7 on fresh Romaine lettuce using a novel bacteriophage lysin

Review on sterilization techniques, and the application potential of phage lyase and lyase immobilization in fighting drug-resistant bacteria

Many human health problems and property losses caused by pathogenic contamination cannot be underestimated. Bactericidal techniques have been extensively studied to address this issue of public health and economy. Bacterial resistance develops as a result of the extensive use of single or multiple but persistent usage of sterilizing drugs, and the emergence of super-resistant bacteria brings new challenges. Therefore, it is crucial to control pathogen contamination by applying innovative and effective sterilization techniques. As organisms that exist in nature and can specifically kill bacteria, phages have become the focus as an alternative to antibacterial agents. Furthermore, phage-encoded lyases are proteins that play important roles in phage sterilization. The in vitro sterilization of phage lyase has been developed as a novel biosterilization technique to reduce bacterial resistance and is more environmentally friendly than conventional sterilization treatments. For the shortcomings of enzyme applications, this review discusses the enzyme immobilization methods and the application potential of immobilized lyases for sterilization. Although some techniques provide effective solutions, immobilized lyase sterilization technology has been proven to be a more effective innovation for efficient pathogen killing and reducing bacterial resistance. We hope that this review can provide new insights for the development of sterilization techniques.

Engineering strategies and challenges of endolysin as an antibacterial agent against Gram-negative bacteria

Bacteriophage endolysin is a novel antibacterial agent that has attracted much attention in the prevention and control of drug-resistant bacteria due to its unique mechanism of hydrolysing peptidoglycans. Although endolysin exhibits excellent bactericidal effects on Gram-positive bacteria, the presence of the outer membrane of Gram-negative bacteria makes it difficult to lyse them extracellularly, thus limiting their application field. To enhance the extracellular activity of endolysin and facilitate its crossing through the outer membrane of Gram-negative bacteria, researchers have adopted physical, chemical, and molecular methods. This review summarizes the characterization of endolysin targeting Gram-negative bacteria, strategies for endolysin modification, and the challenges and future of engineering endolysin against Gram-negative bacteria in clinical applications, to promote the application of endolysin in the prevention and control of Gram-negative bacteria.

Exploring Disease Management and Control through Pathogen Diagnostics and One Health Initiative: A Concise Review

The "One Health" initiative is a critical strategy that recognizes the interconnectedness between human, animal, and environmental health in the spread and containment of infectious pathogens. With the ease of global transportation, transboundary disease outbreaks pose a significant threat to food safety and security, endangering public health and having a negative economic impact. Traditional diagnostic techniques based on genotypic and phenotypic analyses are expensive, time-consuming, and cannot be translated into point-of-care tools, hindering effective disease management and control. However, with advancements in molecular methods, biosensors, and new generation sequencing, rapid and reliable diagnostics are now available. This review provides a comprehensive insight into emergent viral and bacterial pathogens and antimicrobial resistance, highlighting the importance of "One Health" in connecting detection and effective treatment. By emphasizing the symbiotic relationship between human and animal health, this paper underscores the critical role of "One Health" initiatives in preventing and controlling infectious diseases.

Accumulation of colicin M protein and its biological activity in transgenic lettuce and mizuna plants

Food-borne illnesses caused by pathogenic Escherichia coli strains, especially enterohaemorrhagic E. coli (EHEC), are a serious public health problem, as debilitating disease and even death from such food poisonings have been repeatedly reported. Colicin M (ColM), a non-antibiotic antimicrobial protein produced by some strains of E. coli, has shown promising activity in controlling multiple enteropathogenic strains of E. coli and related pathogens. As contaminated green leafy vegetables are a frequent source of pathogenic E. coli infections, we genetically modified (GM) two edible crops, lettuce (Lactuca sativa L.) and mizuna (Brassica rapa subsp. nipposinica var. laciniata), to stably express the ColM gene and assessed the antibacterial activity of tissue extracts from these plants against selected E. coli strains in vitro. Transgenic plants of these species were developed using Agrobacterium-mediated transformation with a vector containing the ColM-coding gene (cma) under the control of the 35S promoter. Western blot analysis of recombinant ColM protein was performed in selected transgenic plants to confirm cma gene expression and quantify ColM accumulation. Extracts of transgenic plants expressing ColM showed significant activity against two major strains of EHEC (O157:H7 and O104:H4) as well as E. coli strains resistant to beta-lactam- and carbapenem-class antibiotics. Importantly, the antibacterial activity persisted in several subsequent generations of transgenic lettuce and mizuna plants that stably expressed the ColM gene. In addition, our results also show that the antibacterial activity of dried (up to 40°C) biomass of transgenic plants remained stable without a decrease for at least three months.

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.

Antibacterial Activity of a Lysin LysP53 against Streptococcus mutans

Dental caries is a common disease affecting quality of life globally. In the present study, we found that a bacteriophage lysin LysP53 against Acinetobacter baumannii possesses selective activity on Streptococcus mutans, the main etiological agent of dental caries, even in low pH caries microenvironments, whereas only minor LysP53 activity was detected against Streptococcus sanguinis, Streptococcus oralis, and Streptococcus mitis. Testing activity against S. mutans planktonic cells showed that 4 μM LysP53 could kill more than 84% of S. mutans within 1 min in buffer with optimal pHs ranging from 4.0 to 6.5. Daily application of LysP53 on biofilms formed in BHI medium supplemented or not with sucrose could reduce exopolysaccharides, expression of genes related to acid resistance and adhesion, and the number of live bacteria in the biofilms. LysP53 treatment also showed similar effects as 0.12% chlorhexidine in preventing enamel demineralization due to S. mutans biofilms, as well as effective removal of S. mutans colonization of tooth surfaces in mice without observed toxic effects. Because of its selective activity against main cariogenic bacteria and good activity in low pH caries microenvironments, it is advantageous to use LysP53 as an active agent for preventing caries.

LysP53 activity against Salmonella and its application in decontamination of Salmonella on fresh romaine lettuce

Salmonella is a zoonotic pathogen that is commonly associated with foodborne disease outbreaks. This study found that a newly identified Gram-negative lysin LysP53 had good activity against a wide range of Salmonella, including Salmonella Newington, Salmonella Typhimurium, and Salmonella Dublin. Without the help of an outer membrane permeabilizer, 4 μM LysP53 could reduce 97.6% of planktonic Salmonella Enteritidis and 90% of the bacteria in biofilms. Moreover, LysP53 was highly thermostable because it maintained >90% activity even after exposure to temperatures up to 95 °C. Although high concentrations of salts could reduce the activity, LysP53 was found safe for oral gavage of mice without affecting body weights and cytokines in sera and able to reduce 90% of Salmonella Enteritidis loads on fresh romaine lettuce after 30 min of treatment. Because of its good activity against a wide range of bacteria, thermal stability, safe for oral administration, LysP53 could be used as a biocontrol agent for reducing bacterial loads in fresh vegetable food. KEY POINTS: • Lysin LysP53 has high bactericidal activity against Salmonella. • LysP53 is thermostable even at high temperature of up to 95 °C. • LysP53 can be used for topical decontamination of Salmonella on vegetables.

PlyKp104, a Novel Phage Lysin for the Treatment of Klebsiella pneumoniae, Pseudomonas aeruginosa, and Other Gram-Negative ESKAPE Pathogens

Klebsiella pneumoniae and Pseudomonas aeruginosa are two leading causes of burn and wound infections, pneumonia, urinary tract infections, and more severe invasive diseases, which are often multidrug resistant (MDR) or extensively drug resistant. Due to this, it is critical to discover alternative antimicrobials, such as bacteriophage lysins, against these pathogens. Unfortunately, most lysins that target Gram-negative bacteria require additional modifications or outer membrane permeabilizing agents to be bactericidal. We identified four putative lysins through bioinformatic analysis of Pseudomonas and Klebsiella phage genomes in the NCBI database and then expressed and tested their intrinsic lytic activity in vitro. The most active lysin, PlyKp104, exhibited >5-log killing against K. pneumoniae, P. aeruginosa, and other Gram-negative representatives of the multidrug-resistant ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, K. pneumonia, Acinetobacter baumannii, P. aeruginosa, and Enterobacter species) without further modification. PlyKp104 displayed rapid killing and high activity over a wide pH range and in high concentrations of salt and urea. Additionally, pulmonary surfactants and low concentrations of human serum did not inhibit PlyKp104 activity in vitro. PlyKp104 also significantly reduced drug-resistant K. pneumoniae >2 logs in a murine skin infection model after one treatment of the wound, suggesting that this lysin could be used as a topical antimicrobial against K. pneumoniae and other MDR Gram-negative infections.

Antibacterial Activity and Possible Mechanism of Litsea cubeba Essential Oil Against Shigella sonnei and Its Application in Lettuce

Shigella sonnei, the causative agents of bacillary dysentery, remains a significant threat to public health. Litsea cubeba essential oil (LC-EO), one of the natural essential oils, exhibited promising biological activities. In this study, the antibacterial effects and possible mechanisms of LC-EO on S. sonnei and its application in lettuce medium were investigated. The minimum inhibitory concentration (MIC) of LC-EO against S. sonnei ATCC 25931 and CMCC 51592 was 4 and 6 μL/mL, respectively. The LC-EO could inhibit the growth of S. sonnei, and decreased S. sonnei to undetectable levels with 4 μL/mL for 1 h in Luria-Bertani broth. The antibacterial mechanism indicated that after the treatment of LC-EO, the production of reactive oxygen species and the activity of superoxide dismutase were significantly elevated in S. sonnei cells, and eventually led to the lipid oxidation product, the malondialdehyde content that significantly increased. Moreover, LC-EO at 2 MIC could destroy 96.51% of bacterial cell membrane integrity, and made S. sonnei cells to appear wrinkled with a rough surface, so that the intracellular adenosine triphosphate leakage was about 0.352-0.030 μmol/L. Finally, the results of application evaluation indicated that the addition of LC-EO at 4 μL/mL in lettuce leaves and 6 μL/mL in lettuce juice could decrease the number of S. sonnei to undetectable levels without remarkable influence on the lettuce leaf sensory quality. In summary, LC-EO exerted strong antibacterial activity and has the potential to control S. sonnei in food industry.

Combine thermal processing with polyvalent phage LPEK22 to prevent the Escherichia coli and Salmonella enterica contamination in food

Thermal processing is the most frequently used method to destruct bacteria in food processing. However, insufficient thermal processing may lead to the outbreak of foodborne illness. This study combined thermal processing with thermostable phage to prevent food contamination. The thermostable phages were screened which can retain activity at 70 °C for 1 h. Among them, the polyvalent phage LPEK22 was obtained to lyse Escherichia coli and Salmonella enterica, especially several multi-drug resistant bacteria. In milk (liquid food matrix), LPEK22 significantly reduced the E. coli by 5.00 ± 0.18 log₁₀ CFU/mL and S. enterica by 4.20 ± 0.23 log₁₀ CFU/mL after thermal processing at 63 °C for 30 min. For beef sausage (solid food matrix), LPEK22 significantly reduced the E. coli by 2.34 ± 0.17 log₁₀ CFU/cm² and S. enterica by 1.54 ± 0.13 log₁₀ CFU/cm² after thermal processing at 66 °C for 90 s. Genome analysis revealed that LPEK22 was a novel phage with a unique tail spike protein belonging to the family of Ackermannviridae. LPEK22 did not contain lysogenic, drug-resistant, and virulent genes that may compromise the safety of food application. These results determined that LPEK22, a novel polyvalent Ackermannviridae phage, could combine with thermal processing to prevent drug-resistant E. coli and S. enterica both in vitro and in foods.

Effect of lysin EN4 in combination with sodium bicarbonate on reduction of Salmonella in chilled and thawed chicken meat

Lysin EN4 is a peptidoglycan-degrading enzyme. Like other lysins against Gram-negative bacteria, EN4 requires cell-wall destabilizing agents, such as ethylenediamine tetraacetic acid (EDTA) to facilitate it to the peptidoglycan layer. This study aimed to use EN4 in reducing Salmonella in chilled and thawed raw chicken meat. However, the use of EDTA is limited to some types of foods. An alternative to EDTA was explored. Sodium bicarbonate was identified as an effective alternative to EDTA. The combination of EN4 with 0.1 % NaHCO₃, pH 7.4 showed a wide lytic spectrum against Salmonella spp. The combination showed efficiency in reduction of Salmonella Enteritidis and Typhimurium in raw chicken meat during storage at 4 °C for 48 h, with the maximum reduction of 1.0-1.3log CFU/g. The efficiency of the combination against Salmonella was evaluated in frozen chicken meat during proper and improper defrosting. A significant reduction of Salmonella was observed in EN4-treated meat compared to the untreated control through 48 and 4 h of defrosting at 4 and 30 °C, respectively, with the greatest reduction of 1.2-1.6 log CFU/g. The results indicated that EN4 in combination with NaHCO₃ has a potential use for controlling growth of Salmonella in chilled and thawed chicken meat.

Recent Progress in Phage Therapy to Modulate Multidrug-Resistant Acinetobacter baumannii, including in Human and Poultry

Acinetobacter baumannii is a multidrug-resistant and invasive pathogen associated with the etiopathology of both an increasing number of nosocomial infections and is of relevance to poultry production systems. Multidrug-resistant Acinetobacter baumannii has been reported in connection to severe challenges to clinical treatment, mostly due to an increased rate of resistance to carbapenems. Amid the possible strategies aiming to reduce the insurgence of antimicrobial resistance, phage therapy has gained particular importance for the treatment of bacterial infections. This review summarizes the different phage-therapy approaches currently in use for multiple-drug resistant Acinetobacter baumannii, including single phage therapy, phage cocktails, phage-antibiotic combination therapy, phage-derived enzymes active on Acinetobacter baumannii and some novel technologies based on phage interventions. Although phage therapy represents a potential treatment solution for multidrug-resistant Acinetobacter baumannii, further research is needed to unravel some unanswered questions, especially in regard to its in vivo applications, before possible routine clinical use.

Duck sewage source coliphage P762 can lyse STEC and APEC

Multiple pathogenic types or serotypes restrict treatment for colibacillosis. In addition, rising antibiotic resistance has heightened public awareness to prevent and control pathogenic Escherichia coli. The bacteriophage is a viable technique to treat colibacillosis as an alternative to antibiotics. P762, a coliphage isolated from duck farm sewage, was demonstrated to cloud lyse Shiga toxin-producing Escherichia Coli serotypes O157 and non-O157 (17/39), Avian pathogenic E. coli covered serotype O78, O83, and O9 (5/19), and other pathogenic Escherichia coli (5/17). Additional fundamental biological characteristics analysis revealed that P762 is stable at pH 3 ~ 11 and temperature between 4 °C and 60 °C, and its optimum multiplicity of infection (MOI) is 0.1. The one-step curve of P762 exhibited three bursts of growth stage: two rapid and one slow stage. Furthermore, the first rapid burst size is 80 CFU/PFU, the burst size of the slow stage is 10 CFU/PFU, and the second rapid burst size is about 990 CFU/PFU. In addition, P762 can form a "halo" on a double agar plate, implying that the phage secretes depolymerase. With 95.14% identity and 90% query coverage, genome sequence analysis revealed that P762 is most closely related to Escherichia phage DY1, which belongs to the genus Kayfunavirus. After screening using RAST and VFDB, no virulence factors were discovered in P762. In vitro antibacterial tests revealed that P762 has high bactericidal activity in lettuce leaves contaminated with STEC. In conclusion, phage P762 might be employed in the future to prevent and control pathogenic Escherichia coli.

Biocontrol Approaches against Escherichia coli O157:H7 in Foods

Shiga-toxin-producing Escherichia coli O157:H7 is a well-known water- and food-borne zoonotic pathogen that can cause gastroenteritis in humans. It threatens the health of millions of people each year; several outbreaks of E. coli O157:H7 infections have been linked to the consumption of contaminated plant foods (e.g., lettuce, spinach, tomato, and fresh fruits) and beef-based products. To control E. coli O157:H7 in foods, several physical (e.g., irradiation, pasteurization, pulsed electric field, and high-pressure processing) and chemical (e.g., using peroxyacetic acid; chlorine dioxide; sodium hypochlorite; and organic acids, such as acetic, lactic, and citric) methods have been widely used. Although the methods are quite effective, they are not applicable to all foods and carry intrinsic disadvantages (alteration of sensory properties, toxicity, etc.). Therefore, the development of safe and effective alternative methods has gained increased attention recently. Biocontrol agents, including bacteriophages, probiotics, antagonistic bacteria, plant-derived natural compounds, bacteriocins, endolysins, and enzymes, are rapidly emerging as effective, selective, relatively safe for human consumption, and environmentally friendly alternatives. This paper summarizes advances in the application of biocontrol agents for E. coli O157:H7 control in foods.

Phages and Enzybiotics in Food Biopreservation

Presently, biopreservation through protective bacterial cultures and their antimicrobial products or using antibacterial compounds derived from plants are proposed as feasible strategies to maintain the long shelf-life of products. Another emerging category of food biopreservatives are bacteriophages or their antibacterial enzymes called "phage lysins" or "enzybiotics", which can be used directly as antibacterial agents due to their ability to act on the membranes of bacteria and destroy them. Bacteriophages are an alternative to antimicrobials in the fight against bacteria, mainly because they have a practically unique host range that gives them great specificity. In addition to their potential ability to specifically control strains of pathogenic bacteria, their use does not generate a negative environmental impact as in the case of antibiotics. Both phages and their enzymes can favor a reduction in antibiotic use, which is desirable given the alarming increase in resistance to antibiotics used not only in human medicine but also in veterinary medicine, agriculture, and in general all processes of manufacturing, preservation, and distribution of food. We present here an overview of the scientific background of phages and enzybiotics in the food industry, as well as food applications of these biopreservatives.

Application of a novel phage vB_SalS-LPSTLL for the biological control of Salmonella in foods

Salmonella is one of the most common foodborne pathogens around the world. Phages are envisioned as a new strategy to control foodborne pathogenic bacteria and food safety. A Salmonella specific lytic phage vB_SalS-LPSTLL (LPSTLL) was selected for food applications on the basis of lytic range, lytic efficiency, functional stability and characteristics. Phage LPSTLL was able to lyse 11 Salmonella serotypes, which represents the broadest range reported Salmonella phages, and was able to suppress the growth of Salmonella enterica in liquid culture over nine hours. LPSTLL exhibited rapid reproductive activity with a short latent period and a large burst size in one-step growth experiment. LPSTLL remained active over a pH range of 3.0 to 12.0, and at incubation temperatures up to 60 °C for 60 min, indicating wide applicability for food processing and storage. Significant reductions of viable Salmonella were observed in diverse foods (milk, apple juice, chicken and lettuce) with reductions up to 2.8 log CFU/mL recorded for milk. Sensory evaluation indicated that treatment with phage LPSTLL did not alter the visual or tactile quality of food matrices. Genome analysis of LPSTLL indicated the absence of any virulence or antimicrobial resistance genes. Genomic comparisons suggest phage LPSTLL constitutes a novel member of a new genus, the LPSTLLvirus with the potential for Salmonella biocontrol in the food industry.