Bacteriocins as antimicrobial and preservative agents in food: Biosynthesis, separation and application

Fermentation starters and bacteriocins as biocontrol strategies for table olives preservation: a mini-review

Biopreservation is a powerful strategy to prolong the shelf life of food products by applying naturally occurring microorganisms and/or their metabolites. Current food trends emphasise the need to develop alternatives for chemical or thermal preservation methods. In this line, different fermentation starters from table olives present the potential to control spoilage or pathogen-occurring microorganism in table olives storage. One of the most interesting family used as biopreservative culture is Lactobacillaceae and it has also been used in combination with yeasts as olive fermentation starter. Lactic acid bacteria, from Lactobacillaceae family, are characterised by the production of bacteriocins, proteins with the potential for preserving food by changing the organisation of the membrane of spoilage microorganisms. These bacteriocins-producing bacteria can be directly inoculated, although nanosystem technology is the most promising incorporation strategy. In table olives, the most commonly used starters are Lactiplantibacillus plantarum, Lactiplantibacillus pentosus, Saccharomyces cerevisiae, Wickerhamomyces anomalus, among others. These strains with biopreservation characteristics, inoculated alone or in mixed cultures, ensure food safety by conferring the product added value and prolonging product shelf life. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Purification, characterization, and mechanistic studies of Gassericin GA-3.1: A novel class IIc bacteriocin produced by Lactobacillus gasseri LG145

Bacteriocins, naturally derived antimicrobial peptides, are considered promising alternatives to traditional preservatives and antibiotics, particularly in food and medical applications. Despite extensive research on various bacteriocins, cyclic varieties remain understudied. This study introduces Gassericin GA-3.1, a novel cyclic bacteriocin produced by Lactobacillus gasseri LG145. We employed a multi-step purification process, including salt precipitation, ion-exchange chromatography, gel filtration chromatography, and ultimately high-performance liquid chromatography (HPLC), achieving a specific activity of 4660.89 AU/mg for the purified Gassericin GA-3.1. Mass spectrometry revealed a molecular mass of 5613.842 Da. Genome analysis confirmed Gassericin GA-3.1 as a novel class IIc bacteriocin with a unique amino acid sequence. Secondary structure prediction suggested the presence of three α-helices, two β-pleated strands, and a random coil. Physicochemical characterization demonstrated GassericinGA-3.1's thermal stability, resistance to pH extremes, surfactants, and broad-spectrum antibacterial potency. Notably, Gassericin GA-3.1 effectively inhibit Listeria monocytogenes through mechanism involving surface perforation, membrane potential disruption, and downregulation of virulence, biofilm formation, and motility genes. Overall, our finding position Gassericin GA-3.1 as a potential candidate for antimicrobial applications in the food and health industries.

Harnessing the Power of Bacteriocins: A Comprehensive Review on Sources, Mechanisms, and Applications in Food Preservation and Safety

The Sustainable Development Goals (SDGs) emphasize the importance of food safety, prolonged shelf life, and reduced food waste, all of which rely on effective food preservation methods. Bacteriocins, natural antimicrobial substances produced by lactic acid bacteria (LAB), have potential applications in food preservation. This review highlights the role of LAB-derived bacteriocins in preserving food. Bacteriocins are highly effective against foodborne infections because they target cell membranes, break down enzymes, and interfere with cellular activities. The following study used molecular docking to understand the interaction of bacteriocins and their mode of action. With their natural origin and specific action, bacteriocins offer a promising strategy for preventing foodborne diseases and extending shelf life without impacting sensory characteristics. However, challenges such as stable manufacturing, regulatory hurdles, and cost effectiveness hinder the wide adoption of bacteriocins. Nevertheless, LAB-derived bacteriocins offer a safe and efficient approach to improving food preservation, enhancing food safety, and reducing reliance on artificial preservatives. Moreover, immobilized bacteriocins have the potential to be integrated into antimicrobial packaging films, providing a targeted way to reduce the risk of foodborne pathogen contamination and improve food safety. Exploring novel bacteriocins presents exciting opportunities for advancing food preservation and safety. The present study also highlights recent advancements in food preservation through bacteriocins.

A Comprehensive Review on Preparation of Silver Nanoparticles from a Bacteriocin for the Natural Preservation of Food Products

Food preservation aims to maintain safe and nutritious food for extended periods by inhibiting microbial growth that causes spoilage and poses health risks. Traditional chemical preservatives like sodium sulfite, sodium nitrite, sodium benzoate, tBHQ and BHA have raised concerns due to potential carcinogenicity, genotoxicity and allergies with long-term consumption. As a natural alternative, bacteriocins have emerged for food preservation. These ribosomally synthesised antimicrobial peptides are produced by various microorganisms, including bacteria, fungi and yeast, typically during their stationary growth phase. Bacteriocins are categorised into four classes based on structure and function, with molecular weights averaging between 30 and 80 kDa. They exhibit antimicrobial activity against a range of bacteria, mediating complex interactions between bacterial species and enhancing competitiveness and survival of producer strains. Both gram-positive and gram-negative bacteria produce bacteriocins. Recent advancements have identified and optimized bacteriocins for applications in food technology, extending shelf life, managing foodborne illnesses and contributing to public health preservation. Their eco-friendly nature and safety profile make bacteriocins promising for future food preservation strategies without detrimental effects on humans or animals. The current review has mainly focused on the preservation of food products using bacteriocin.

The potential of Streptococcus pyogenes and Escherichia coli bacteriocins in synergistic control of Staphylococcus aureus

Staphylococcus aureus has developed resistance to most conventional antibiotics and is a causative agent of serious infections. Alternative therapies are urgently needed. Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria, including Escherichia coli (E. coli) and Streptococcus pyogenes (S. pyogenes), and represent a potential solution. While several bacteriocins have shown promise, their synergy with bacteriocins from other bacterial species remains largely unexplored. This work used agar diffusion on Muller-Hinton Agar (MHA) with S. aureus as a test bacterium to evaluate E. coli, S. pyogenes and their combined bacteriocins. The bacteriocins of S. pyogenes showed the maximum antimicrobial activity of zone of inhibition (ZOI), 24.93 mm, compared to that of E. coli bacteriocin, which was 19.28 mm, and that of the combined ones at 100% concentration, 22.6 mm. The combined bacteriocins at 50% concentration showed a reduced activity of 18.35 mm. These observations suggest that the bacteriocins produced by S. pyogenes have higher specificity and activity against S. aureus, making them effective therapeutic agents in the fight against multidrug-resistant infections.

Synergizing postharvest physiology and nanopackaging for edible mushroom preservation

The cultivation of edible mushrooms is increasing because of their widely recognized nutritional benefits. Advancements in cultivation techniques have facilitated large-scale mushroom production, meeting the growing consumer demand. This rise in cultivation has led to an increasingly urgent demand for advanced postharvest preservation methods to extend the shelf life of these mushrooms. The postharvest preservation of fresh edible mushrooms involves complex physiological changes and metabolic activities closely associated with gas composition, microbial presence, moisture content, ambient temperature, and enzymatic activity. Preserving edible mushrooms through various preservation strategies (physical, chemical, biological, and nanopackaging approaches) relies on regulating postharvest factors. Nanopackaging can preserve mushrooms' sensory and nutritional qualities due to the specific characteristics of nanomaterials, such as antimicrobial properties and gas/moisture barriers. Furthermore, the review explores current trends, fundamental mechanisms, and upcoming challenges in utilizing nanomaterials, particularly their capacity to enhance the "cell wall" integrity of edible mushrooms by regulating postharvest factors.

Microbial bioprotection: An opportunity to improve safety and quality of meat products in a sustainable way

In a changing world where sustainability has become a must, the food system has been identified as one of the weakest links where there is a need for innovative solutions to address longstanding and novel challenges related to food safety and quality. The current food system is facing enormous pressure to tackle environmental sustainability issues while guaranteeing safety and diversifying production. In the last years, the possibility to exploit naturally occurring competitive mechanisms, which regulate the homeostasis of microbial ecosystems, has attracted a lot of attention and interest. More specifically, in the food transformation sector, bacteriocins and bacteriocinogenic microorganisms have long been considered an innovation tool attracting the attention of the researchers and industries due to their potential application in the meat sector. This paper presents an analysis of the opportunities and the challenges of the use of bioprotection, also called biopreservation, in the food system as sustainable strategy to be implemented in meat production. Specifically methodologies to identify bacteriocinogenic strains, the effect of processing conditions on the expression of bacteriocin genes and the efficacy of bacteriocin producing strains to inhibit not only target microorganisms but whole spoilage consortia will be discussed.

Current challenges and development strategies of bacteriocins produced by lactic acid bacteria applied in the food industry

Given the great importance of natural biopreservatives in the modern food industry, lactic acid bacteria (LAB)-producing bacteriocins have gained considerable attention due to their antimicrobial activity against foodborne pathogens and spoilage bacteria. Although numerous LAB-producing bacteriocins have demonstrated efficiency in preserving food quality in various applications, only a limited number of these compounds have been commercially approved to date. The currently unclear gastrointestinal metabolism of bacteriocins may pose safety risks, as well as cytotoxicity and immunogenicity, which need to be seriously considered before their application. A more noteworthy concern lies in whether bacteriocins induce an imbalance in the gut microbiota, thereby leading to alterations in the abundance of health-associated microorganisms and their metabolites in the gastrointestinal tract. Accordingly, this review presents unique insights into the challenges arising from metabolic interactions between LAB-producing bacteriocins and the gastrointestinal tract. Besides, the application of bacteriocins in the food industry faces challenges arising from the low production yield, weak stability, and insufficient antimicrobial activity. The corresponding development strategies are proposed for conducting the systematic and comprehensive evaluation of the potential safety risks of bacteriocins and their metabolites. The strategies also focus on the rational design to increase the activity and stability, the fermentation control to enhance the production yield, and the hurdle and embedding technology to improve the application effects. It definitively discloses the perspective of bacteriocins to become natural, sustainable, safe, and eco-friendly biological preservatives for the advancement of the food industry.

Antineoplastic with DNA fragmentation assay and anti-oxidant, anti-inflammatory with gene expression activity of Lactobacillus plantarum isolated from local Egyptian milk products

Many lactic acid bacteria (LAB), known for their human health benefits, are derived from milk and utilized in biotherapeutic applications or for producing valuable nutraceuticals. However, the specific role of milk-associated LAB in biotherapeutics remains underexplored. To address this, eight milk product samples were randomly selected from the Egyptian market, diluted, and then cultured anaerobically on MRS agar. Subsequently, 16 suspected LAB isolates were recovered and underwent rapid preliminary identification. Among these isolates, the Lactobacillus plantarum strain with accession number (OQ547261.1) was identified due to its strong antioxidant activity depending on the DPPH assay, L. plantarum displayed notable antioxidant activities of 71.8% and 93.8% at concentrations of 125-1000 µg/mL, respectively. While ascorbic acid showed lower concentrations of 7.81, 3.9, and 1.95 µg/mL which showed activities of 45.1%, 34.2%, and 27.2%, respectively. The anti-inflammatory efficacy of L. plantarum was evaluated based on its capability to prevent hemolysis induced by hypotonic conditions. At a concentration of 1000 µg/mL, L. plantarum could reduce hemolysis by 97.7%, nearly matching the 99.5% inhibition rate achieved by the standard drug, indomethacin, at an identical concentration. Moreover, L. plantarum exhibited high hemolytic activity at 100 µg/mL (14.3%), which decreased to 1.4% at 1000 µg/mL. The abundance of phenolic acids and flavonoids was determined by high-performance liquid chromatography (HPLC) in L. plantarum. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) demonstrated that L. plantarum increased gene expression of the inflammatory marker TLR2 by 133%, and cellular oxidation markers SOD1 and SOD2 by 65% and 74.2%, respectively, while suppressing CRP expression by 33.3%. These results underscore L. plantarum's exceptional anti-inflammatory and antioxidant activities. Furthermore, L. plantarum induces cancer cell death through necrotic nuclear DNA fragmentation. These findings suggest that L. plantarum is not only suitable for nutraceutical production but also holds potential as a probiotic strain. Future research should focus on enhancing the capacity of this strain across various industries and fostering innovation in multiple fields.

Understanding of probiotic origin antimicrobial peptides: a sustainable approach ensuring food safety

The practice of preserving and adding value to food dates back to over 10,000 BCE, when unintentional microbial-driven chemical reactions imparted flavor and extended the shelf life of fermented foods. The process evolved, and with the urbanization of society, significant shifts in dietary habits emerged, accompanied by sporadic food poisoning incidents. The repercussions of the COVID-19 pandemic have intensified the search for antibiotic alternatives owing to the rise in antibiotic-resistant pathogens, emphasizing the exploration of probiotic-origin antimicrobial peptides to alleviate human microbiome collateral damage. Often termed 'molecular knives', these peptides outstand as potent antimicrobials due to their compatibility with innate microflora, amenability to bioengineering, target specificity, versatility and rapidity in molecular level mode of action. This review centres on bacteriocins sourced from lactic acid bacteria found in ethnic fermented foods, accentuating their desirable attributes, technological applications as nanobiotics and potential future applications in the modern context of ensuring food safety.

Insight into the Probiogenomic Potential of Enterococcus faecium BGPAS1-3 and Application of a Potent Thermostable Bacteriocin

This study aimed to investigate the probiogenomic features of artisanal bacteriocin-producing Enterococcus faecium BGPAS1-3 and the use of the improved pMALc5HisEk expression vector for overexpressing class II bacteriocins and the application of purified bacteriocin 31 in a milk model as a preservative against L. monocytogenes. The BGPAS1-3 strain was isolated from traditional fresh soft cheese manufactured in households on a small scale in rural locations surrounding Pale Mountain City in Bosnia and Herzegovina. The whole-genome sequencing approach and bioinformatics analyses revealed that the strain BGPAS1-3 was non-pathogenic to humans. The presence of bacteriocin operons suggested the ability of the isolate to suppress the growth of pathogens. Coding regions for three maturated bacteriocins (bacteriocin 31, bacteriocin 32, and enterocin P) produced by BGPAS1-3 were amplified and expressed in Escherichia coli ER2523 using the pMALc5HisEk system. All three bacteriocins were successfully overexpressed and purified after enterokinase cleavage but showed different antimicrobial activity. Bacteriocin 31 showed significantly stronger antimicrobial activity compared with bacteriocin 32. It was the only one that proved to be suitable for use as a food preservative against L. monocytogenes in a milk model.

Biosynthesis of bacteriocin BacZY05-silver nanoconjugates and evaluation of their antibacterial properties

Bacteriocins are antimicrobial peptides produced by bacteria to prevent the growth of pathogens. Combining bacteriocins with metal nanoparticles, like silver nanoparticles (AgNPs), has developed into a viable strategy to get over bacteriocin limitations. In this study, bacteriocin BacZY05 was extracted from Bacillus subtilis ZY05 and purified using various techniques. The resulting purified bacteriocin was then combined with silver nanoparticles to form bacteriocin silver nanoconjugates (BacZY05-AgNPs). The physicochemical properties of the BacZY05-AgNPs were characterized using various analytical techniques. The mean diameter of the synthesized AgNPs was approximately 20-60 nm with an oval or spherical shape. The antimicrobial activity of the BacZY05-AgNPs was evaluated against several indicator strains by their zone of inhibition (ZOI), using the agar well diffusion method. Compared to bacteriocin (ZOI- 13 to 20 mm) and AgNPs (ZOI- 10-22 mm) alone, the antibacterial activity data demonstrated a 1.3-1.5-fold increase in the activity of bacteriocin-nanoconjugates (ZOI- 22 to 26 mm). For Staphylococcus aureus MTCC3103 and Klebsiella pneumoniae MTCC109, BacZY05-capped AgNPs exhibited the lowest minimum inhibitory concentration (MIC), measuring 10.93 µg/mL. For Salmonella typhi NCIM2501, the MIC was 28.75 µg/mL. The highest MIC value was 57.5 µg/mL for Escherichia coli DH5α and Vibrio cholerae MTCC3909. With BacZY05-capped AgNPs, the lowest minimum bactericidal concentration (MBC) of 28.75 µg/mL was observed for Staphylococcus aureus MTCC31003. In the cases of Salmonella typhi NCIM2501 and Klebsiella pneumoniae MTCC109 concentration was 57.5 µg/mL. Vibrio cholerae MTCC3909 and Escherichia coli DH5α had the highest MBC values at 115 µg/mL.

Recent Advances in the Application of Natural Products for Postharvest Edible Mushroom Quality Preservation

Edible mushrooms are favored by consumers for their excellent nutritional value and pharmacological properties. However, fresh mushrooms are highly perishable and undergo rapid quality deterioration induced by a series of intrinsic and extrinsic factors during postharvest storage. In recent years, the application of natural products derived from plants, animals, microorganisms, and other sources in mushroom quality preservation has drawn increasing attention. Compared to chemical preservatives, natural products show similar or higher biological activity and have few side effects on human health. This review summarizes the recent advances in the application of natural products used for quality maintenance of postharvest mushrooms. These natural substances mainly include essential oils, polyphenols, polysaccharides, bacteriocins, and other extracts. They have the potential to inhibit mushroom weight loss, softening, and browning, reduce the count of pathogenic microorganisms, and retain nutrients and flavor, effectively improving the quality of mushrooms and extending their shelf-life. The preservation techniques for natural products and their preservation mechanisms are also discussed here. Overall, this review provides current knowledge about natural products in edible mushroom preservation and aims to inspire more in-depth theoretical research and promote further practical application.

Classification and Multi-Functional Use of Bacteriocins in Health, Biotechnology, and Food Industry

Bacteriocins is the name given to products of the secondary metabolism of many bacterial genera that must display antimicrobial activity. Although there are several bacteriocins described today, it has not been possible to reach a consensus on the method of classification for these biomolecules. In addition, many of them are not yet authorized for therapeutic use against multi-drug-resistant microorganisms due to possible toxic effects. However, recent research has achieved considerable progress in the understanding, classification, and elucidation of their mechanisms of action against microorganisms, which are of medical and biotechnological interest. Therefore, in more current times, protocols are already being conducted for their optimal use, in the hopes of solving multiple health and food conservation problems. This review aims to synthetize the information available nowadays regarding bacteriocins, and their classification, while also providing an insight into the future possibilities of their usage for both the pharmaceutical, food, and biotechnological industry.

Application of Natural Functional Additives for Improving Bioactivity and Structure of Biopolymer-Based Films for Food Packaging: A Review

The global trend towards conscious consumption plays an important role in consumer preferences regarding both the composition and quality of food and packaging materials, including sustainable ones. The development of biodegradable active packaging materials could reduce both the negative impact on the environment due to a decrease in the use of oil-based plastics and the amount of synthetic preservatives. This review discusses relevant functional additives for improving the bioactivity of biopolymer-based films. Addition of plant, microbial, animal and organic nanoparticles into bio-based films is discussed. Changes in mechanical, transparency, water and oxygen barrier properties are reviewed. Since microbial and oxidative deterioration are the main causes of food spoilage, antimicrobial and antioxidant properties of natural additives are discussed, including perspective ones for the development of biodegradable active packaging.

Subinhibitory concentrations of nisin enhance virulence gene expression in Staphylococcus aureus and increase mortality in Galleria mellonella

Alternative strategies for controlling Staphylococcus aureus and other pathogens have been continuously investigated, with nisin, a bacteriocin widely used in the food industry as a biopreservative, gaining increasing attention. In addition to its antimicrobial properties, bacteriocins have significant effects on genome functionality even at inhibitory concentrations. This study investigated the impact of subinhibitory concentrations of nisin on S. aureus. Culturing in the presence of 0.625 μmol l-1 nisin, led to the increased relative expression of hla, saeR, and sarA, genes associated with virulence while expression of the sea gene, encoding staphylococcal enterotoxin A (SEA), decreased. In an in vivo experiment, Galleria mellonella larvae inoculated with S. aureus cultured in the presence of nisin exhibited 97% mortality at 72 h post-infection, compared to over 40% of larvae mortality in larvae infected with S. aureus. A comprehensive understanding of the effect of nisin on the transcriptional response of virulence genes and the impact of these changes on the virulence of S. aureus can contribute to assessing the application of this bacteriocin in food and medical contexts.

Economic impact of subclinical mastitis treatment in early lactation using intramammary nisin

Treatment of subclinical mastitis (SCM) during lactation is rarely recommended due to concerns related to both antimicrobial usage and the costs associated with milk discard. Nisin is a naturally produced antimicrobial peptide with a gram-positive spectrum that, when given to dairy cows, does not require milk discard. We evaluated the economic impact of the treatment of SCM during early lactation using a nisin-based intramammary treatment under different scenarios that included various treatment costs, milk prices, and cure rates. We stochastically simulated the dynamics of SCM detected during the first week of lactation. The net economic impact was expressed in US dollars per case. The probabilities of an event and their related costs were estimated using a model that was based on pathogen-specific assumptions selected from peer-reviewed articles. Nisin cure rates were based on results of pivotal studies included in the US Food and Drug Administration (FDA) approval submission. Based on our model, the average cost of a case of intramammary infection (i.e., only true-positive cases) in early lactation was $170 (90% = $148-$187), whereas the cost of a clinical mastitis case was $521 (90% range = $435-$581). Both estimates varied with etiology, parity, and stage of lactation. When comparing the net cost of SCM cases (i.e., CMT-positive tests) detected during the first week of lactation, nisin treatment generated an average positive economic impact of $19 per CMT-positive case. The use of nisin to treat SCM was beneficial 93% of the time. Based on the sensitivity analysis, treatment would result in an economically beneficial outcome for 95% and 73% of multiparous and primiparous cows, respectively. At the herd level, use of intramammary nisin to treat SCM in cows in early lactation was economically beneficial in most tested scenarios. However, the economic impact was highly influenced by factors such as rate of bacteriological cure, cost of treatment, and parity of the affected animal. These factors should be considered when deciding to use nisin as a treatment for SCM.

Bacteriocins attenuate Listeria monocytogenes-induced intestinal barrier dysfunction and inflammatory response

Bacteriocins have the potential to effectively improve food-borne infections or gastrointestinal diseases and hold promise as viable alternatives to antibiotics. This study aimed to explore the antibacterial activity of three bacteriocins (nisin, enterocin Gr17, and plantaricin RX-8) and their ability to attenuate intestinal barrier dysfunction and inflammatory responses induced by Listeria monocytogenes, respectively. Bacteriocins have shown excellent antibacterial activity against L. monocytogenes without causing any cytotoxicity. Bacteriocins inhibited the adhesion and invasion of L. monocytogenes on Caco-2 cells, lactate dehydrogenase (LDH), trans-epithelial electrical resistance (TEER), and cell migration showed that bacteriocin improved the permeability of Caco-2 cells. These results were attributed to the promotion of tight junction proteins (TJP) assembly, specifically zonula occludens-1 (ZO-1), occludin, and claudin-1. Furthermore, bacteriocins could alleviate inflammation by inhibiting the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) pathways and reducing the secretion of interleukin-6 (IL-6), interleukin-1 β (IL-1β) and tumor necrosis factor α (TNF-α). Among three bacteriocins, plantaricin RX-8 showed the best antibacterial activity against L. monocytogenes and the most pronounced protective effect on the intestinal barrier due to its unique structure. Based on our findings, we hypothesized that bacteriocins may inhibit the adhesion and invasion of L. monocytogenes by competing adhesion sites. Moreover, they may further enhance intestinal barrier function by inhibiting the expression of L. monocytogenes virulence factors, increasing the expression of TJP and decreasing the secretion of inflammatory factors. Therefore, bacteriocins will hopefully be an effective alternative to antibiotics, and this study provides valuable insights into food safety concerns. KEY POINTS: • Bacteriocins show excellent antibacterial activity against L. monocytogenes • Bacteriocins improve intestinal barrier damage and inflammatory response • Plantaricin RX-8 has the best protective effect on Caco-2 cells damage.

Time-resolved cell-to-cell heterogeneity of Listeria innocua after nisin exposure

The use of bacteriocins is a promising approach for addressing the immense threat of food-borne and drug-resistant pathogens. In recent years screening platforms for novel bacteriocins using whole-cell biosensors have been established. During screening cell-to-cell heterogeneity is currently neglected but might play a crucial role in signal development of the whole-cell biosensor after bacteriocin exposure. In this study, we explored the temporal dynamics of the signal heterogeneity of the biosensor Listeria innocua LMG2785/pNZpHin2 Lm after nisin exposure using microfluidic single-cell analysis. The results provided novel and detailed insights into the dynamics of cell-to-cell heterogeneity in L. innocua LMG2785/pNZpHin2 Lm at different nisin concentrations with a high spatio-temporal resolution. Furthermore, the formation of subpopulations during bacteriocin exposure was observed. In-depth single-cell tracking even revealed the regeneration of disrupted cells and recovery of pH homeostasis in rare instances. These findings are highly important for the future design and execution of bacteriocin assays and for the interpretation of fluorescence signal development at the population level after exposure to different concentrations of bacteriocins (here, nisin), as well as for obtaining deeper insights into single-cell persistence strategies to quantify the efficacy and efficiency of novel bacteriocins.

Bio-Preservation Potential and Antimicrobial Activity of Bacteriocin-Producing Lactic Acid Bacteria Isolated from Ethiopian Traditional Fermented Dairy Products

This study aimed to assess the antibacterial activity and bio-preservation capability of bacteriocin-producing LAB isolated from Ethiopian traditional fermented dairy products in raw milk from Jimma town. Bacteriocin-producing LAB were tested for their antimicrobial activity against various foodborne pathogens, including Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium. The results showed that probiotic LAB isolates inhibited foodborne pathogens (E. coli, S. aureus, and L. monocytogenes), with inhibition zones ranging from 22.00 ± 0.57 to 34.13 ± 0.57. Enterococcus faecium and Lactococcus lactis demonstrated possible antagonistic effects against E. coli, while Pediococcus pentosaceus had a 34.13 ± 0.57 mm inhibitory zone against Pseudomonas aeruginosa. The isolates also showed co-aggregation potential with the pathogens, with Lactococcus lactis isolates and their combinations demonstrating the best co-aggregation capabilities against the investigated pathogens. The bio-preservative assay showed that putative probiotic isolates (L. lactis JULABE35, E. faecium JULABE 23, and P. pentosaceus JULABE05) were efficient in decreasing Listeria monocytogenes in raw milk. After 7-8 days, milk samples diagnosed with these isolates showed complete reduction of Listeria monocytogenes. The bio-preservation capability of bacteriocin-producing LAB on raw milk extended the shelf life of milk at 4 °C storage for ten days, compared to six days for milk samples without probiotic LAB. The milk samples preserved with probiotic and bacteriocin-producing isolates showed good proximate analysis, showing significant variation with milk kept without bacteriocin-producing isolates. The isolated chemicals employed in this study can be used as food additives or food preservatives, indicating potential applications in Ethiopian traditional fermented dairy products.

Lactic Acid Bacteria isolated from traditional and innovative alheiras as potential biocontrol agents

From a selection of seven traditional and 14 innovative alheiras, 491 lactic acid bacteria (LAB) were isolated and tested for their antimicrobial activity against several food-borne pathogens. Among these, six strains revealed antimicrobial activity through potential bacteriocin production against 14 Listeria monocytogenes strains, Enterococcus faecalis ATCC 29212, Clostridium sporogenes ESB050, and Clostridium perfringens ESB054. Through whole genome sequencing (WGS), these strains were identified as Lactiplantibacillus plantarum (2), Leuconostoc mesenteroides (1), and Pediococcus acidilactici (3). Furthermore, several orthologues of class II bacteriocins genes were identified, including Plantaricin E, Plantaricin F, Pediocin PA, Enterocin X, Leucocin A, and Coagulin A. No virulence or antibiotic resistance genes' orthologues were detected by WGS analysis. However, the selected LAB strains showed variable phenotypic patterns related to virulence genes and antibiotic resistance when assessed through classical methodologies. None of these strains demonstrated the production of biogenic amines, gelatinase or DNase. Additionally, no hemolytic activity or lipase enzyme production was observed. However, only Lpb. plantarum 9A3 was sensitive to all tested antibiotics and was thus chosen for further examination. The bacteriocins produced by Lpb. plantarum (9A3) exhibited stability across a broad range of conditions, including temperatures from 4 to 100 °C, pH values ranging from 2 to 8, exposure to surfactants and detergents (Tween 20 and 80, SDS, EDTA 0.1, 2 and 5 mM, urea and sodium deoxycholate), and enzymes (papain and catalase). Their maximum activity (AU/mL = 12,800) against four L. monocytogenes strains was observed between 21 and 36 h of growth of Lbp. plantarum 9A3, indicating a bacteriostatic mode of action. Therefore, this strain appears to be a robust candidate for potential application as a protective strain to be used in the food industry. Not only is it safe, but it also produces stable bacteriocins (harbouring genes encoding for the production of three) effectively inhibiting significant pathogens such as L. monocytogenes and C. perfringens.

Blue Biotechnology: Marine Bacteria Bioproducts

The ocean is the habitat of a great number of organisms with different characteristics. Compared to terrestrial microorganisms, marine microorganisms also represent a vast and largely unexplored reservoir of bioactive compounds with diverse industrial applications like terrestrial microorganisms. This review examines the properties and potential applications of products derived from marine microorganisms, including bacteriocins, enzymes, exopolysaccharides, and pigments, juxtaposing them in some cases against their terrestrial counterparts. We discuss the distinct characteristics that set marine-derived products apart, including enhanced stability and unique structural features such as the amount of uronic acid and sulfate groups in exopolysaccharides. Further, we explore the uses of these marine-derived compounds across various industries, ranging from food and pharmaceuticals to cosmetics and biotechnology. This review also presents a broad description of biotechnologically important compounds produced by bacteria isolated from marine environments, some of them with different qualities compared to their terrestrial counterparts.

Symbiotic microparticles produced through spray-drying-induced in situ alginate crosslinking for the preservation of Pediococcus pentosaceus viability

Probiotic microorganisms are a promising alternative to antibiotics in preventing and treating bacterial infections. Within the probiotic group, the lactic acid bacteria (LAB)stand out for their health benefits and for being recognized as safe by regulatory agencies. However, these microorganisms are sensitive to various environmental conditions, including the acidic environment of the stomach. Faced with these obstacles, this work aimed to promote the symbiotic microencapsulation of LAB in a composite matrix of alginate and prebiotics to enhance their survival and improve their probiotic activity during gastrointestinal transit. We evaluated the effect of inulin, fructo-oligosaccharides (FOS) and mannan-oligosaccharides (MOS) as prebiotic sources on the growth of Pediococcus pentosaceus LBM34 strain, finding that MOS favored LAB growth and maintenance of microencapsulated cell viability. The symbiotic microparticles were produced using the spray-drying technique with an average size of 10 μm, a smooth surface, and a composition that favored the stabilization of live cells according to the FTIR and the thermal analysis of the material. The best formulation was composed of 1 % of alginate, 10 % MOS and 1 % M10 (% w/v), which presented notable increases in the survival rates of the probiotic strain in both alkaline and acidic conditions. Therefore, this industrially scalable approach to symbiotic LAB microencapsulation can facilitate their growth and colonization within the host. This effort aims to contribute to reducing antibiotic reliance and mitigating the emergence of new zoonotic diseases, which pose significant challenges to public health.

Anti-Listerial Activity of Bacteriocin-like Inhibitory Substance Produced by Enterococcus lactis LBM BT2 Using Alternative Medium with Sugarcane Molasses

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, thus reaching final products by cross-contamination. With the growing demand for clean-label products, the search for natural antimicrobials as biopreservants, such as bacteriocins, has shown promising potential. In this context, this study aimed to evaluate the anti-listerial action of bacteriocins produced by Enterococcus lactis LBM BT2 in an alternative medium containing sugarcane molasses (SCM). Molecular analyses were carried out to characterize the strain, including the presence of bacteriocin-related genes. In the kinetic study on SCM medium E. lactis, LBM BT2 showed biomass and bacteriocin productions similar to those observed on a sucrose-based medium (control), highlighting the potential of the sugarcane molasses as a low-cost substrate. Stability tests revealed that the molecule remained active in wide ranges of pH (4-10) and temperature (60-100 °C). Furthermore, the proteolytic treatment reduced the biomolecule's antimicrobial activity, highlighting its proteinaceous nature. After primary purification by salting out and tangential flow filtration, the bacteriocin-like inhibitory substance (BLIS) showed bacteriostatic activity on suspended L. monocytogenes cells and against biofilm formation at a concentration of 0.625 mg/mL. These results demonstrate the potential of the produced BLIS as a biopreservative in the food industry.

Lactobacillaceae differentially impact butyrate-producing gut microbiota to drive CNS autoimmunity

BACKGROUND

Short-chain fatty acids (SCFAs), produced by the gut microbiota, are thought to exert an anti-inflammatory effect on the host immune system. The levels of SCFAs and abundance of the microbiota that produce them are depleted in multiple sclerosis (MS), an autoimmune disease of the central nervous system (CNS). The mechanisms leading to this depletion are unknown. Using experimental autoimmune encephalomyelitis (EAE) as a model for MS, we have previously shown that gut microbiomes divergent in their abundance of specific commensal Lactobacillaceae, Limosilactobacillus reuteri (L. reuteri) and Ligilactobacillus murinus (L. murinus), differentially impact CNS autoimmunity. To determine the underlying mechanisms, we employed colonization by L. reuteri and L. murinus in disparate gut microbiome configurations in vivo and in vitro, profiling their impact on gut microbiome composition and metabolism, coupled with modulation of dietary fiber in the EAE model.

RESULTS

We show that stable colonization by L. reuteri, but not L. murinus, exacerbates EAE, in conjunction with a significant remodeling of gut microbiome composition, depleting SCFA-producing microbiota, including Lachnospiraceae, Prevotellaceae, and Bifidobacterium, with a net decrease in bacterial metabolic pathways involved in butyrate production. In a minimal microbiome culture model in vitro, L. reuteri directly inhibited SCFA-producer growth and depleted butyrate. Genomic analysis of L. reuteri isolates revealed an enrichment in bacteriocins with known antimicrobial activity against SCFA-producing microbiota. Functionally, provision of excess dietary fiber, as the prebiotic substrate for SCFA production, elevated SCFA levels and abrogated the ability of L. reuteri to exacerbate EAE.

CONCLUSTIONS

Our data highlight a potential mechanism for reduced SCFAs and their producers in MS through depletion by other members of the gut microbiome, demonstrating that interactions between microbiota can impact CNS autoimmunity in a diet-dependent manner. These data suggest that therapeutic restoration of SCFA levels in MS may require not only dietary intervention, but also modulation of the gut microbiome.

Anti-Salmonella Activity of a Novel Peptide, KGGDLGLFEPTL, Derived from Egg Yolk Hydrolysate

The present study aimed to characterize the mode of action of a novel antimicrobial peptide isolated from egg yolk hydrolysate. The EYHp6, KGGDLGLFEPTL, exhibited inhibition against Salmonella enterica serovar Typhimurium TISTR 292 and S. enterica serovar Enteritidis DMST 15679 with a MIC value of 2 mM. In contrast, S. enterica serovar Newport ATCC 6962 and other strains of Typhimurium and Enteritidis were inhibited at 4 mM. EYHp6 increased the cell membrane permeability of S. Typhimurium TISTR 292, leading to DNA leakage. Membrane integrity determined by propidium iodide and SYTO9 staining visualized by confocal microscopy demonstrated that EYHp6 at 1 × MIC induced disruption of cell membranes. Electron microscopy revealed that treatment of S. Typhimurium with EYHp6 led to damage to the cell membrane, causing the leakage of intracellular contents. Synchrotron-based Fourier-transform infrared spectroscopy indicated that EYHp6 killed S. Typhimurium by targeting fatty acids and nucleic acids in the cell membrane. The peptide did not show hemolytic activity up to 4 mM. These findings suggest that EYHp6 could be a promising antibacterial agent for controlling the growth of S. enterica.

Insight into the Postbiotic Potential of the Autochthonous Bacteriocin-Producing Enterococcus faecium BGZLM1-5 in the Reduction in the Abundance of Listeria monocytogenes ATCC19111 in a Milk Model

This study aimed to explore the probiogenomic characteristics of artisanal bacteriocin-producing Enterococcus faecium BGZLM1-5 and its potential application in reducing Listeria monocytogenes in a milk model. The BGZLM1-5 strain was isolated from raw cow's milk from households in the Zlatar Mountain region. The whole genome sequencing approach and bioinformatics analyses reveal that the strain BGZLM1-5 is non-pathogenic to humans. Bacteriocin-containing supernatant was thermally stable and antimicrobial activity retained 75% of the initial activity compared with that of the control after treatment at 90 °C for 30 min. Antimicrobial activity maintained relative stability at pH 3-11 and retained 62.5% of the initial activity compared with that of the control after treatment at pH 1, 2, and 12. The highest activity of the partially purified bacteriocin was obtained after precipitation at 40% saturation with ammonium sulfate and further purification by mixing with chloroform. Applying 3% and 5% (v/v) of the bacteriocin-containing supernatant and 0.5% (v/v) of the partially purified bacteriocin decreased the viable number of L. monocytogenes ATCC19111 after three days of milk storage by 23.5%, 63.5%, and 58.9%, respectively.

Antimicrobial activity of thermophilin 110 against the opportunistic pathogen Cutibacterium acnes

OBJECTIVE

Thermophilin 110, a bacteriocin produced by Streptococcus thermophilus B59671, inhibited planktonic growth and biofilm formation of Cutibacterium acnes, a commensal skin bacterium associated with the inflammatory disease, acne vulgaris, and more invasive deep tissue infections.

RESULTS

Thermophilin 110 prevented planktonic growth of C. acnes at a concentration ≥ 160 AU mL-1; while concentrations ≥ 640 AU mL-1 resulted in a > 5 log reduction in viable planktonic cell counts and inhibited biofilm formation. Arabinoxylan (AX) and sodium alginate (SA) hydrogels were shown to encapsulate thermophilin 110, but as currently formulated, the encapsulated bacteriocin was unable to diffuse out of the gel and inhibit the growth of C. acnes. Hydrogels were also used to encapsulate S. thermophilus B59671, and inhibition zones were observed against C. acnes around intact SA gels, or S. thermophilus colonies that were released from AX gels.

CONCLUSIONS

Thermophilin 110 has potential as an antimicrobial for preventing C. acnes infections and further optimization of SA and AX gel formulations could allow them to serve as delivery systems for bacteriocins or bacteriocin-producing probiotics.

Evaluating the Translational Potential of Bacteriocins as an Alternative Treatment for Staphylococcus aureus Infections in Animals and Humans

Antibiotic resistance remains a global threat to human and animal health. Staphylococcus aureus is an opportunistic pathogen that causes minor to life-threatening infections. The widespread use of antibiotics in the clinical, veterinary, and agricultural setting combined with the increasing prevalence of antibiotic-resistant S. aureus strains makes it abundantly clear that alternatives to antibiotics are urgently needed. Bacteriocins represent one potential alternative therapeutic. They are antimicrobial peptides that are produced by bacteria that are generally nontoxic and have a relatively narrow target spectrum, and they leave many commensals and most mammalian cells unperturbed. Multiple studies involving bacteriocins (e.g., nisin, epidermicin, mersacidin, and lysostaphin) have demonstrated their efficacy at eliminating or treating a wide variety of S. aureus infections in animal models. This review provides a comprehensive and updated evaluation of animal studies involving bacteriocins and highlights their translational potential. The strengths and limitations associated with bacteriocin treatments compared with traditional antibiotic therapies are evaluated, and the challenges that are involved with implementing novel therapeutics are discussed.

Roles of inter- and intramolecular tryptophan interactions in membrane-active proteins revealed by racemic protein crystallography

Tryptophan is frequently found on the surface of membrane-associated proteins that interact with the lipid membrane. However, because of their multifaceted interactions, it is difficult to pinpoint the structure-activity relationship of each tryptophan residue. Here, we describe the use of racemic protein crystallography to probe dedicated tryptophan interactions of a model tryptophan-rich bacteriocin aureocin A53 (AucA) by inclusion and/or exclusion of potential ligands. In the presence of tetrahedral anions that are isosteric to the head group of phospholipids, distinct tryptophan H-bond networks were revealed. H-bond donation by W40 was critical for antibacterial activity, as its substitution by 1-methyltryptophan resulted in substantial loss of activity against bacterial clinical isolates. Meanwhile, exclusion of tetrahedral ions revealed that W3 partakes in formation of a dimeric interface, thus suggesting that AucA is dimeric in solution and dissociated to interact with the phosphate head group in the presence of the lipid membrane. Based on these findings, we could predict the tryptophan residue responsible for activity as well as the oligomeric state of a distant homologue lacticin Q (48%).

Microbial Inhibition by UV Radiation Combined with Nisin and Shelf-Life Extension of Tangerine Juice during Refrigerated Storage

This study evaluated the efficiency of UV radiation doses (4.68-149.76 J/cm²) and nisin (50-200 ppm) and their combination in comparison with thermal pasteurization on the microbial inhibition kinetics and physicochemical properties of tangerine juice. It was noted that UV-149.76 J/cm² and nisin (NS) at 200 ppm in conjunction exhibited the highest log reduction in spoilage and pathogenic microbes including Escherichia coli, Lactiplantibacillus plantarum, and Saccharomyces cerevisiae, yeast and molds, and total plate count in tangerine juice. Additionally, the first-order kinetic model provides a better fit for spoilage and pathogenic strains compared with the zero-order model (higher coefficient of determination, R²), particularly for E. coli. UV and NS showed insignificant effects (p > 0.05) on pH, TSS, and TA values compared with pasteurization. However, there were notable differences observed in color analysis, total phenolic compound, total flavonoid content, vitamin C, carotenoid content, and antioxidant activity using DPPH and FRAP assays. The optimized UV + NS samples were subjected to refrigerated storage for 21 days. The results revealed that during the entire storage period, the pH values and the TSS values slightly decreased, and the TA values increased in the treated samples. The UV + NS treatment insignificantly impacted the color properties. The total phenolic, total flavonoid, and carotenoid contents, and vitamin C decreased over time for all sample treatments, whereas the antioxidant properties exhibited varying outcomes, compared with an untreated control and pasteurization. Therefore, UV radiation and nisin (UV-149.76 J/cm² + NS-200 ppm) in combination could serve as a viable alternative to traditional heat pasteurization of fruit juice during cold storage.

Lactic acid bacteria in the functional food industry: biotechnological properties and potential applications

With the growing demand for functional foods having better nutraceutical properties, lactic acid bacteria (LAB) has become an important industrial microorganism. LAB play a significant role in the functional food industry by exhibiting probiotic properties and has the ability to produce various biologically active metabolites such as γ-aminobutyric acid (GABA), exopolysaccharides (EPSs), conjugated linoleic acid (CLA), bacteriocins, reuterin and reutericyclin, which provides enhanced nutraceutical properties to the final food products. LAB are also known to produce several specific enzymes essential for producing substrate-derived bioactive compounds, such as polyphenols, bioactive peptides, inulin-type fructans and β-glucans, fatty acids, and polyols. These compounds exhibit many health benefits, including better mineral absorption, oxidative stress protection, blood glucose and cholesterol-lowering properties, prevention of gastrointestinal tract infections and improved cardiovascular function. Further, metabolically engineered LAB have been widely used for the nutritive enhancement of different food products and the application of CRISPR-Cas9 holds tremendous potential for the engineering of food cultures. This review provides an overview of the use of LAB as probiotics, its application in producing fermented foods and nutraceutical products, and its health benefits on the host.

In Situ Inactivation of Selected Bacillus Strains in Brewer's Spent Grain during Fermentation by Lactococcus lactis ATCC 11454-The Possibility of Post-Production Residues Management

The safety and quality of post-production residues is essential before they can be reused. Both to explore the possibility of reuse as a fermentation medium and the context of pathogens' inactivation, the research aimed to characterize the fermentation system of L. lactis ATCC 11454 and brewer's spent grain, malt and barley, especially to in situ inactivation of selected Bacillus strains during the fermentation and storage. Barley products were milled, autoclaved, hydrated and fermented with L. lactis ATCC 11454. Then, the co-fermentation with Bacillus strains was carried out. The amount of polyphenols in the samples ranged from 483.5 to 718.4 ug GAE g^-1 and increased after 24 h fermentation with L. lactis ATCC 11454. The high viability of LAB in the fermented samples and after 7 days of storage at 4 °C (8 log CFU g^-1) indicates the high nutrients bioavailability during the storage. Also, this co-fermentation on different barley products indicated a high reduction level (2 to 4 logs) of Bacillus due to the biosuppression effect of the LAB strain in this fermentation system. Brewer's spent grain (BSG) fermented with L. lactis ATCC 25 11454 produces a highly effective cell-free supernatant (CFS) for suppressing Bacillus strains. This was evident in both the inhibition zone and fluorescence analysis of bacteria viability. In conclusion, the obtained results justify the use of brewer's spent grain in selected food products, increasing their safety and nutritional value. This finding is highly beneficial in the sustainable management of post-production residues when current waste material can still serve as a source of food.

Lacto-fermented garlic sauce improved the quality and extended the shelf life of lamb meat under the chilled condition

This study evaluated the potential of fermented garlic as a marinated lamb sauce ingredient to improve the quality and shelf life of chilled lamb. Garlic was subjected to Lacto-fermentation for 72 h at 37 °C using Lacticaseibacillus casei. The ¹H NMR metabolomics profile showed the presence of eight amino acids and five organic acids in fermented garlic, indicating the attribution to the antioxidant and antimicrobial activities. The FRAP and DPPH assays of fermented garlic revealed antioxidant activities of 0.45 ± 0.09 mmol/100 g DW and 93.85 ± 0.02 %, respectively. Meanwhile, fermented garlic inhibited the growth of Escherichia coli (95 %), Staphylococcus aureus (99 %) and Salmonella Typhimurium (98 %). When fermented garlic was added to the marinade sauce, it successfully reduced the microbial load of lamb meat by 0.5 log CFU/g after 3 days of storage. There were no significant differences in color between the control and marinated lamb after 3 days of marinating in a sauce formulated with fermented garlic. Furthermore, marinated lamb significantly improved water-holding capacity, texture, juiciness, and overall acceptance. These findings indicated a potential addition of fermented garlic in marinade lamb sauce recipes to improve the quality and safety of meat products.

Optimizing the effects of nisin and nacl to thermal inactivate listeria monocytogenes in ground beef with chipotle sauce during sous-vide processing

Mild cooking thermal treatments, like sous-vide, can compromise ground meat entrees such as meatballs with chipotle sauce, especially when salt levels are reduced during its preparation. Listeria monocytogenes is a thermoresistant pathogen that can be in ready-to-eat food. On the other hand, nisin, due to its thermal stability, can be a good alternative to aid on the thermal inactivation of L. monocytogenes and ensure meat safety. The objective was to optimize the amount of nisin and salt concentrations to thermally inactivate L. monocytogenes during the sous-vide cooking of ground beef marinated in chipotle sauce, and to generate a predictive model. A four-strain cocktail was prepared and inoculated in ground beef in combination (3:2) with chipotle sauce added with nisin (0-150 IU) and salt (0-2%). After that, meat samples were sous-vide cooked at different temperatures, nisin, and salt concentrations, established by a central composite design. Depending on the levels of these factors, D-values ranged from 49.71 to 0.27 min. A predictive model (p < 0.05) was obtained by response surface, which described that D-values variation was explained by the linear effects of the three factors, the interaction between nisin and temperature, and the quadratic effects of salt and temperature. It was also observed that nisin presented a bactericidal effect while salt presented a protective effect during the thermal inactivation of L. monocytogenes. Adding 120 IU of nisin and 0.4% of salt to the meat product at 63°C temperature can help to ensure food safety by making L. monocytogenes cells more sensitive to the lethal effect of heat. The model developed in this study can be used by food processors for planning and designing effective levels of salt and nisin to thermally inactivate L. monocytogenes in ground beef products marinated with chipotle sauce to ensure their safety.

Quorum-quenching enzymes: Promising bioresources and their opportunities and challenges as alternative bacteriostatic agents in food industry

The problems of spoilage, disease, and biofilm caused by bacterial quorum-sensing (QS) systems have posed a significant challenge to the development of the food industry. Quorum-quenching (QQ) enzymes can block QS by hydrolyzing or modifying the signal molecule, making these enzymes promising new candidates for use as antimicrobials. With many recent studies of QQ enzymes and their potential to target foodborne bacteria, an updated and systematic review is necessary. Thus, the goals of this review were to summarize what is known about the effects of bacterial QS on the food industry; discuss the current understanding of the catalytic mechanisms of QQ enzymes, including lactonase, acylase, and oxidoreductase; and describe strategies for the engineering and evolution of QQ enzymes for practical use. In particular, this review focuses on the latest progress in the application of QQ enzymes in the field of food. Finally, the current challenges limiting the systematic application of QQ enzymes in the food industry are discussed to help guide the future development of these important enzymes.

Bacteriocin Production by Escherichia coli during Biofilm Development

Escherichia coli is a highly versatile bacterium ranging from commensal to intestinal pathogen, and is an important foodborne pathogen. E. coli species are able to prosper in multispecies biofilms and secrete bacteriocins that are only toxic to species/strains closely related to the producer strain. In this study, 20 distinct E. coli strains were characterized for several properties that confer competitive advantages against closer microorganisms by assessing the biofilm-forming capacity, the production of antimicrobial molecules, and the production of siderophores. Furthermore, primer sets for E. coli bacteriocins–colicins were designed and genes were amplified, allowing us to observe that colicins were widely distributed among the pathogenic E. coli strains. Their production in the planktonic phase or single-species biofilms was uncommon. Only two E. coli strains out of nine biofilm-forming were able to inhibit the growth of other E. coli strains. There is evidence of larger amounts of colicin being produced in the late stages of E. coli biofilm growth. The decrease in bacterial biomass after 12 h of incubation indicates active type I colicin production, whose release normally requires E. coli cell lysis. Almost all E. coli strains were siderophore-producing, which may be related to the resistance to colicin as these two molecules may use the same transporter system. Moreover, E. coli CECT 504 was able to coexist with Salmonella enterica in dual-species biofilms, but Shigella dysenteriae was selectively excluded, correlating with high expression levels of colicin (E, B, and M) genes observed by real-time PCR.

Thurincin H Is a Nonhemolytic Bacteriocin of Bacillus thuringiensis with Potential for Applied Use

Thurincin H, a bacteriocin produced by Bacillus thuringiensis, exhibits antibacterial activity against Gram-positive and Gram-negative bacteria. While much is known about its expression and antimicrobial spectrum, its hemolytic property has yet to be established. In this study, thurincin H was produced in a plasmid-free acrystalliferous strain of B. thuringiensis (Bt Cry^-B) that naturally lacked antimicrobial and hemolytic activities. When grown in Tryptic Soy Broth (TSB), the bacteriocin's maximal production in Bt Cry^-B harboring the thurincin H genetic cluster (Bt Cry^-B/pThur) was observed at 24 h. Thurincin H was purified as a sole peptide of ~5 kDa using three purification steps, i.e., salt precipitation, ultrafiltration, and gel filtration chromatography. The bacteriocin showed inhibitory activity against B. cereus (5631 U), Bt Cry^-B (8827 U), E. faecium wild type (11,197 U), and E. faecium ATCC 19,434 (6950 U), but not against Bt Cry^-B/pThurH and Bt Cry^-B/pThurHΔThnA. In addition, a minimum inhibitory concentration (MIC) of 5.0 μg/mL against B. cereus 183 was observed. In silico predictions suggested that thuricin H lacks hemolytic activity, which was validated in vitro using 4 × the MIC, i.e., 20 μg/ml. Our data lay a foundation for the potential safe use of thurincin H as an antibacterial peptide for medical use, in food products, and for expression in probiotic bacteria.

Co-Delivery of Nano-Silver and Vancomycin via Silica Nanopollens for Enhanced Antibacterial Functions

Infectious diseases caused by bacteria have led to a great threat to public health. With the significant advances in nanotechnology in recent decades, nanomaterials have emerged as a powerful tool to boost antibacterial performance due to either intrinsic bactericidal properties or by enhancing the delivery efficiency of antibiotics for effective pathogen killing. Vancomycin, as one of the most widely employed antimicrobial peptides, has a potent bactericidal activity, but at the same time shows a limited bioavailability. Silver nanoparticles have also been extensively explored and were found to have a well-recognized antibacterial activity and limited resistance potential; however, how to prevent nanosized Ag particles from aggregation in biological conditions is challenging. In this study, we aimed to combine the advantages of both vancomycin and nano-Ag for enhanced bacterial killing, where both antibacterial agents were successfully loaded onto a silica nanoparticle with a pollen-like morphology. The morphology of nano-Ag-decorated silica nanopollens was characterized using transmission electron microscopy and elemental mapping through energy dispersive spectroscopy. Silver nanoparticles with a size of 10–25 nm were observed as well-distributed on the surface of silica nanoparticles of around 200 nm. The unique design of a spiky morphology of silica nano-carriers promoted the adhesion of nanoparticles towards bacterial surfaces to promote localized drug release for bacterial killing, where the bacterial damage was visualized through scanning electron microscopy. Enhanced bactericidal activity was demonstrated through this co-delivery of vancomycin and nano-Ag, decreasing the minimum inhibition concentration (MIC) towards E. coli and S. epidermidis down to 15 and 10 µg/mL. This study provides an efficient antimicrobial nano-strategy to address potential bacterial infections.