Purification of novel bacteriocin produced by Lactobacillus coryniformis MXJ 32 for inhibiting bacterial foodborne pathogens including antibiotic-resistant microorganisms

Soft rot of postharvest pepper: bacterial pathogen, pathogenicity and its biological control using Lactobacillus farciminis LJLAB1

BACKGROUND

Soft rot is the most important bacterial disease of postharvest pepper during storage and transportation. The main objectives of this study were to investigate the bacterial pathogen species causing pepper soft rot and seek for an antagonistic bacterium to control this disease.

RESULTS

Pathogens Pectobacterium carotovorum, Enterobacter sp., Klebsiella sp., Pseudomonas sp. and Bacillus sp. were verified to be the causes of soft rot which were isolated from rotten peppers. Among them, P. carotovorum had the highest prevalence, including P. carotovorum subsp. carotovorum (Pcc) and P. carotovorum subsp. brasilisesis (Pcb). The result of pathogenicity analysis showed that Pcb Jm2 had strong pathogenicity at 25 °C even at a cell concentration of 103  CFU mL-1 . Its pathogenicity decreased at 4 °C. Multiple pathogenic factors were identified in the draft genome of Pcb Jm2, including cellulase, pectinase, pectin methylesterase, pectinesterase, pectin lyase, polygalacturonase and so forth. Further, the disease control ability of Lactobacillus farciminis LJLAB1 was investigated. The cell-free supernatant (CFS) and crude bacteriocin of L. farciminis LJLAB1 had good antibacterial activities to Pcb Jm2 in vitro, but CFS exhibited a better disease control effect in vivo. CFS treatment prevented the damage of pepper epidermal structure caused by Pcb Jm2, and 99.26% of pathogen cells on pepper were killed by it. Moreover, CFS treatment delayed firmness decrease, soluble solid content loss, weight loss, yellowing and malonaldehyde accumulation of pepper during storage after pathogen infection.

CONCLUSION

L. farciminis LJLAB1 can be an effective biological control agent to control pepper soft rot caused by Pcb. © 2023 Society of Chemical Industry.

Application of Atmospheric and Room-Temperature Plasma (ARTP) to Microbial Breeding

Atmospheric and room-temperature plasma (ARTP) is an efficient microbial mutagenesis method with broad application prospects. Compared to traditional methods, ARTP technology can more effectively induce DNA damage and generate stable mutant strains. It is characterized by its simplicity, cost-effectiveness, and avoidance of hazardous chemicals, presenting a vast potential for application. The ARTP technology is widely used in bacterial, fungal, and microalgal mutagenesis for increasing productivity and improving characteristics. In conclusion, ARTP technology holds significant promise in the field of microbial breeding. Through ARTP technology, we can create mutant strains with specific genetic traits and improved performance, thereby increasing yield, improving quality, and meeting market demands. The field of microbial breeding will witness further innovation and progress with continuous refinement and optimization of ARTP technology.

Complete Genome Sequencing and Bacteriocin Functional Characterization of Pediococcus ethanolidurans CP201 from Daqu

This study aims to sequence the whole genome of Pediococcus ethanolidurans CP201 isolated from Daqu and determine the anti-corrosion ability of bacteriocins on chicken breast. The whole genome sequence information of P. ethanolidurans CP201 was analyzed, and its gene structure and function were explored. It was found that gene1164 had annotations in the NR, Pfam, and Swiss-Prot databases, and was related to bacteriocins. The exogenous expression of the bacteriocin gene Pediocin PE-201 was analyzed based on the pET-21b vector and the host BL21, and the corresponding bacteriocin was successfully expressed under the induction of IPTG. After purification by NI-NTA column, enterokinase treatment, membrane dialysis concentration treatment, and SDS-PAGE electrophoresis, the molecular weight was about 6.5 kDa and the purity was above 90%. By applying different concentrations of bacteriocin to chicken breast with different levels of contamination, the control of pathogenic bacteria, the ordinary contamination level (OC) group, and the high contamination level (MC) group could be completely achieved with 25 mg/L bacteriocin. In conclusion, the bacteriocin produced by the newly isolated CP201 can be applied to the preservation of meat products to prevent the risk of food-borne diseases.

Therapeutic effect of Lactobacillus plantarum JS19 on mice with dextran sulfate sodium induced acute and chronic ulcerative colitis

BACKGROUND

Ulcerative colitis is associated with intestinal inflammation and dysbiosis. Previous studies have shown that probiotics are potential agents for treatment of inflammatory bowel disease (IBD). Jiang-shui is a traditional fermented vegetable that is rich in lactic acid bacteria (LABs), but the preventive effect of LABs in jiang-shui on IBD is not yet fully understood.

RESULTS

We isolated 38 LAB strains from jiang-shui, and Lactobacillus plantarum JS19 exhibited the strongest antioxidant activity among them. Our data indicate that oral administration of L. plantarum JS19 significantly inhibited body weight loss, colon shortening and damage, and reduced the disease activity index score in the mice with dextran sulfate sodium (DSS)-induced colitis. In addition, L. plantarum JS19 also alleviated inflammatory responses and oxidative stress through reducing lipid peroxidation, tumor necrosis factor-α expression, and myeloperoxidase activity and enhancing the antioxidant enzyme activity. Importantly, L. plantarum JS19 significantly rebalanced DSS-induced dysbiosis of gut microbiota.

CONCLUSION

L. plantarum JS19 may be used as a potential probiotic to prevent IBD, particularly ulcerative colitis. © 2022 Society of Chemical Industry.

Nanomedicine for drug resistant pathogens and COVID-19 using mushroom nanocomposite inspired with bacteriocin – A Review

Multidrug resistant (MDR) pathogens have become a major global health challenge and have severely threatened the health of society. Current conditions have gotten worse as a result of the COVID-19 pandemic, and infection rates in the future will rise. It is necessary to design, respond effectively, and take action to address these challenges by investigating new avenues. In this regard, the fabrication of metal NPs utilized by various methods, including green synthesis using mushroom, is highly versatile, cost-effective, eco-compatible, and superior. In contrast, biofabrication of metal NPs can be employed as a powerful weapon against MDR pathogens and have immense biomedical applications. In addition, the advancement in nanotechnology has made possible to modify the nanomaterials and enhance their activities. Metal NPs with biomolecules composite to prevents their microbial adhesion and kills the microbial pathogens through biofilm formation. Bacteriocin is an excellent antimicrobial peptide that works well as an augmentation substance to boost the antimicrobial effects. As a result, we concentrate on the creation of new, eco-compatible mycosynthesized metal NPs with bacteriocin nanocomposite via electrostatic, covalent, or non-covalent bindings. The synergistic benefits of metal NPs with bacteriocin to combat MDR pathogens and COVID-19, as well as other biomedical applications, are discussed in this review. Moreover, the importance of the adverse outcome pathway (AOP) in risk analysis of manufactured metal nanocomposite nanomaterial and their future possibilities also discussed.

A novel bacteriocin against multiple foodborne pathogens from Lacticaseibacillus rhamnosus isolated from juice ferments: ATF perfusion-based preparation of viable cells, characterization, antibacterial and antibiofilm activity

Foodborne pathogens and their biofilms pose a risk to human health through food chain. However, the bacteriocin resources combating this threat are still limited. Here, Lacticaseibacillus rhamnosus, one of the most used probiotics in food industry, was prepared on a large scale using alternating tangential flow (ATF) perfusion-based technology. Compared to the conventional fed-batch approach, ATF perfusion remarkably increased the viable cells of L. rhamnosus CLK 101 to 11.93 ± 0.14 log CFU/mL. Based on obtained viable cells, we purified and characterized a novel bacteriocin CLK_01 with a broad spectrum of activity against both Gram-positive and Gram-negative foodborne pathogens. LC-MS/MS analysis revealed that CLK_01 has a molecular mass of 701.49 Da and a hydrophobic amino acid composition of I-K-K-V-T-I. As a novel bacteriocin, CLK_01 showed high thermal stability and acid-base tolerance over 25-121 °C and pH 2-10. It significantly reduced cell viability of bacterial pathogens (p < 0.001), and strongly inhibited their biofilm formation. Scanning electron microscopy demonstrated deformation of pathogenic cells caused by CLK_01, leading to cytoplasmic content leakage and bacterial death. Summarily, we employed ATF perfusion to obtain viable L. rhamnosus, and presented that bacteriocin CLK_01 could serve as a promising biopreservative for controlling foodborne pathogenic bacteria and their biofilms.

Purification and characterization of Lactobacillus plantarum-derived bacteriocin with activity against Staphylococcus argenteus planktonic cells and biofilm

Bacteriocins inhibit various foodborne bacteria in planktonic and biofilm forms. However, bacteriocins with antibacterial and antibiofilm activity against Staphylococcus argenteus, a pathogen that can cause food poisoning, are still poorly known. Here, the novel bacteriocin LSB1 derived from Lactobacillus plantarum CGMCC 1.12934 was purified and characterized extensively. LSB1 had a molecular weight of 1425.78 Da and an amino acid sequence of YIFVTGGVVSSLGK. Moreover, LSB1 exhibited excellent stability under heat and acid-base stress and presented sensitivity to pepsin and proteinase K. LSB1 exhibited an extensive antimicrobial spectrum against both Gram-positive and Gram-negative bacteria. Minimum inhibitory concentration of LSB1 against S. argenteus_70917 was 10.36 µg/ml, which was lower than that of most of the previously found bacteriocins against Staphylococcus strains. Furthermore, LSB1 significantly inhibited S. argenteus_70917 planktonic cells (p < 0.01) and decreased their viability. Scanning electron microscopy analysis revealed that cell membrane permeability of S. argenteus_70917 upon exposure to LSB1 showed leakage of cytoplasmic contents and rupture, leading to cell death. In addition, biofilm formation ability of S. argenteus_70917 was significantly (p < 0.01) impaired by LSB1, with the percent inhibition of 35% at 10 µg/ml and 80% at 20 µg/ml. Overall, this study indicates that LSB1 can be considered a potential antibacterial agent in the control of S. argenteus in both planktonic and biofilm states. PRACTICAL APPLICATION: Foodborne pathogenic bacteria, such as Staphylococcus argenteus, and their biofilms represent potential risks for food safety. In recent years, customers' demand for "natural" products has increased food control. This study describes the novel bacteriocin LSB1 produced by the lactic acid bacterium species Lactobacillus plantarum. LSB1 showed strong antibacterial and antibiofilm activity against S. argenteus as well as thermal and acid-alkaline stability. Furthermore, the mechanisms of action of LSB1 on S. argenteus were preliminarily explored. These results indicate that LSB1 might be potentially used as an effective and natural food preservative.

Preservative effects of a novel bacteriocin from Lactobacillus panis C-M2 combined with dielectric barrier discharged cold plasma (DBD-CP) on acquatic foods

In this study, a novel bacteriocin Lactocin C-M2 produced by Lactobacillus panis C-M2, combined with dielectric barrier discharged cold plasma (DBD-CP), was used to evaluate the antibacterial effect on aquatic foods. After the purification procedures of ethyl acetate extraction, cation exchange chromatography and semi-preparative liquid phase, the stability of Lactocin C-M2 under DBD-CP environment was determined, and the preservation effect of these two joint treatments was investigated on fresh white fish samples. As revealed by LC-MS/MS and BLAST analysis, Lactocin C-M2 is a new type of class Ⅱ bacteriocin, with a molecular weight of 863.52 Da and the N-terminal sequence MVKKTSAV. Application of Lactocin C-M2 showed significantly stronger inhibitory effect on bacteria than on yeasts and mold. All the tested 10 Gram positive bacteria and 3 Gram-negative bacteria, including Staphylococcus aureus, Shigella flexneri, Bacillus spp, Lactobacillus spp, Escherichia coli, Pseudomonas aeruginosa, and so on, were inhibited. Lactocin C-M2 also presented stable antibacterial activity after exposure to DBD-CP, with the 95% residual activity against Staphylococcus aureus under the 40∼80 kV voltage for 30∼180 s, indicating the possibility of synergistic application. Combined with addition of 0.9 mg/g Lactocin C-M2, the treatment of DBD-CP with voltage at 60 kV for 90 s on fresh white fish (Culter alburnus) could significantly inhibit the microbial growth, the accumulation of volatile nitrogen and histamine during the storage. Therefore, the Lactocin C-M2, used together with the DBD-CP, is effective in food preservation.

Bacteriocins from lactic acid bacteria and their potential clinical applications

Bacteriocins are ribosomally synthesized antimicrobial peptides that have long been used in the food industry. Being a highly diverse and heterogeneous group of molecules the classification is ever-evolving. Their production is widespread among bacteria; nevertheless, their biosynthesis and mode of action remain fairly similar. With the advances in drug resistance mechanisms, it is important to look for alternatives to conventional approaches. Therefore, the advantages of bacteriocin over antibiotics need to be considered to provide a scientific basis for their use. Particularly in the last decade, intensive studies look at their potential as next-generation therapeutics against drug-resistant bacteria. Bacteriocins from lactic acid bacteria are being tested as controlling agents for bacterial and viral infections; they can inhibit biofilm synthesis and have potential as contraceptives. Bioengineered peptides have shown enhanced activity and thereby indicate the lack of knowledge we possess regarding these bacteriocins. In this review, we have listed various Gram-positive LAB bacteriocins with their synthesis and mechanism of action. Recent developments in screening and purification technologies have been analyzed with an emphasis on their potential clinical applications. Although extensive research has been done to identify multifunctional bacteriocins, it is important to focus on the mechanism of action of these peptides to get them from bench to bedside.

Novel pathways in bacteriocin synthesis by lactic acid bacteria with special reference to ethnic fermented foods

Ethnic fermented foods are known for their unique aroma, flavour, taste, texture and other sensory properties preferred by every ethnic community in this world culturally as parts of their eatables. Some beneficial microorganisms associated with fermented foods have several functional properties and health-promoting benefits. Bacteriocins are the secondary metabolites produced by the microorganisms mostly lactic acid bacteria present in the fermented foods which can act as lantibiotics against the pathogen bacteria. Several studies have been conducted regarding the isolation and characterization of potent strains as well as their association with different types of bacteriocins. Collective information regarding the gene organizations responsible for the potent effect of bacteriocins as lantibiotics, mode of action on pathogen bacterial cells is not yet available. This review focuses on the gene organizations, pathways include for bacteriocin and their mode of action for various classes of bacteriocins produced by lactic acid bacteria in some ethnic fermented foods.

YbfA Regulates the Sensitivity of Escherichia coli K12 to Plantaricin BM-1 via the BasS/BasR Two-Component Regulatory System

Plantaricin BM-1, a class IIa bacteriocin produced by Lactobacillus plantarum BM-1, shows obvious antibacterial activity against Escherichia coli. However, the mechanism underlying the action of class IIa bacteriocins against gram-negative bacteria remains to be explored. The purpose of this study was to investigate the role of YbfA, a DUF2517 domain-containing protein, in the response of Escherichia coli K12 to plantaricin BM-1. The growth curve experiment and MIC experiment showed that the sensitivity of E. coli to plantaricin BM-1 was decreased by a ybfA null mutation. Electron microscopy showed that the ybfA null mutation reduced the surface rupture and contraction caused by plantaricin BM-1, and mitigated the effect of plantaricin BM-1 on the morphology of the E. coli cell membrane. Proteomics analysis showed that 323 proteins were differentially expressed in E. coli lacking the ybfA gene (P < 0.05); 118 proteins were downregulated, and 205 proteins were upregulated. The metabolic pathways containing the upregulated proteins mainly included outer membrane proteins, integral components of the plasma membrane, regulation of cell motility, and regulation of locomotion. The metabolic pathways involving the downregulated proteins mainly included outer membrane protein glycine betaine transport, amino-acid betaine transport, and transmembrane signaling receptor activity. The results of the proteomics analysis showed that the protein expression of the BasS/BasR two-component system was significantly increased (P < 0.05). Moreover, the expression levels of downstream proteins regulated by this two-component system were also significantly increased, including DgkA, FliC, and MlaE, which are involved in cell membrane structure and function, and RT-qPCR also confirmed this result. The growth curve showed that the sensitivity of E. coli to plantaricin BM-1 was significantly increased due to deletion of the BasS/BasR two-component system. Thus, deletion of ybfA in E. coli can increase the expression of the BasS/BasR two-component system and positively regulate the structure and function of the cell membrane to reduce the sensitivity to plantaricin BM-1. This will help to explore the mechanism of action of class IIa bacteriocins against gram-negative bacteria.

Bacteriocins: Recent advances in application as an antimicrobial alternative

Due to the emergence and development of antibiotic resistance in the treatment of bacterial infections, efforts to discover new antimicrobial agents have increased. One of these antimicrobial agents is a compound produced by a large number of bacteria called bacteriocin. Bacteriocins are small ribosomal polypeptides that can exert their antibacterial effects against bacteria close to their producer strain or even non-closely strains. Adequate knowledge of the structure and functional mechanisms of bacteriocins and their spectrum of activity, as well as knowledge of the mechanisms of possible resistance to these compounds will lead to further development of their use as an alternative to antibiotics. Furthermore, most bacteria that live in the gastrointestinal tract (GIT) have the ability to produce bacteriocins, which spread throughout the GIT. Despite antimicrobial studies in vitro, our knowledge of bacteriocins in the GIT and the migration of these bacteriocins from the epithelial barrier is low. Hence, in this study, we reviewed general information about bacteriocins, such as classification, mechanism of action and resistance, emphasizing their presence, stability, and spectrum of activity in the GIT.

Lactobacillus coryniformis MXJ32 administration ameliorates azoxymethane/dextran sulfate sodium-induced colitis-associated colorectal cancer via reshaping intestinal microenvironment and alleviating inflammatory response

PURPOSE

Gut microbiota has been reported to contribute to either prevent or promote colorectal cancer (CRC), and treatment with probiotics might be a promising intervention method. The present study aimed to evaluate the potential anti-CRC effects of Lactobacillus coryniformis MXJ32 on a colitis-associated (CA)-CRC mouse model.

METHODS

The CA-CRC mouse model was induced by a single intraperitoneal injection of 10 mg/kg azoxymethane and followed by three 7-day cycles of 2% dextran sulfate sodium in drinking water with a 14-day recovery period. Mice were supplemented with L. coryniformis MXJ32 by oral gavage (1 × 10⁹ CFU/day/mouse). The CA-CRC attenuating effects of this probiotic were assessed via intestinal barrier integrity, inflammation, and gut microenvironment.

RESULTS

Treatment with L. coryniformis MXJ32 could significantly inhibit the total number of tumors and the average tumor diameter. This probiotic administration prevented the damage of intestinal barrier function by enhancing the expression of tight junction proteins (Occludin, Claudin-1, and ZO-1) and recovering the loss of goblet cells. Moreover, L. coryniformis MXJ32 alleviated intestinal inflammation via down-regulating the expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-γ, and IL-17a) and chemokines (Cxcl1, Cxcl2, Cxcl3, Cxcl5, and Ccl7). In addition, L. coryniformis MXJ32 supplementation increased the abundance of some beneficial bacteria (such as SCFAs-producing bacteria, Lactobacillus, Bifidobacterium, Akkermansia, and Faecalibaculum) and decreased the abundance of some harmful bacteria (such as pro-inflammatory bacteria, Desulfovibrio and Helicobacter), which in turn attenuated the overexpression of inflammation.

CONCLUSION

Lactobacillus coryniformis MXJ32 could effectively ameliorate CA-CRC via regulating intestinal microenvironment, alleviating inflammation, and intestinal barrier damage, which further suggested that L. coryniformis MXJ32 could be considered as a functional food ingredient for the alleviation of CA-CRC.

Therapeutic and Improving Function of Lactobacilli in the Prevention and Treatment of Cardiovascular-Related Diseases: A Novel Perspective From Gut Microbiota

The occurrence and development of cardiovascular-related diseases are associated with structural and functional changes in gut microbiota (GM). The accumulation of beneficial gut commensals contributes to the improvement of cardiovascular-related diseases. The cardiovascular-related diseases that can be relieved by Lactobacillus supplementation, including hypercholesterolemia, atherosclerosis, myocardial infarction, heart failure, type 2 diabetes mellitus, and obesity, have expanded. As probiotics, lactobacilli occupy a substantial part of the GM and play important functional roles through various GM-derived metabolites. Lactobacilli ultimately have a beneficial impact on lipid metabolism, inflammatory factors, and oxidative stress to relieve the symptoms of cardiovascular-related diseases. However, the axis and cellular process of gut commensal Lactobacillus in improving cardiovascular-related diseases have not been fully elucidated. Additionally, Lactobacillus strains produce diverse antimicrobial peptides, which help maintain intestinal homeostasis and ameliorate cardiovascular-related diseases. These strains are a field that needs to be further investigated immediately. Thus, this review demonstrated the mechanisms and summarized the evidence of the benefit of Lactobacillus strain supplementation from animal studies and human clinical trials. We also highlighted a broad range of lactobacilli candidates with therapeutic capability by mining their metabolites. Our study provides instruction in the development of lactobacilli as a functional food to improve cardiovascular-related diseases.

Anti-Adhesion Effects of Lactobacillus Strains on Caco-2 Cells Against Escherichia Coli and Their Application in Ameliorating the Symptoms of Dextran Sulfate Sodium-Induced Colitis in Mice

The beneficial effects of probiotics on ameliorating ulcerative colitis (UC) have attracted much attention in recent years. Nevertheless, the number of these identified probiotics is still limited. In addition, the adhesion abilities of probiotics are considered to be a key determinant for probiotic efficacy. However, the relationship between the adhesion abilities of probiotics and their role in ameliorating UC has been poorly studied to date. This study measured the adhesion abilities of four Lactobacillus strains to Caco-2 cells and their anti-adhesion effects on Caco-2 cells against pathogenic bacteria, as well as their application in ameliorating the symptoms of dextran sulfate sodium-induced UC, and further illustrated the relationship between these two potential probiotic properties of probiotics and their beneficial effects on UC. Results suggested that the adhesion abilities of the four tested Lactobacillus strains exists highly strain-specific and the mechanisms of their anti-adhesion effect on Caco-2 cells against Escherichia coli may be different. Moreover, all these strains had promising effects on ameliorating UC by reducing inflammatory response and improving the intestinal mucosal barrier function, as well as promoting the production of SCFAs. In conclusion, the four tested Lactobacillus strains can be considered as alternative dietary supplements in alleviating UC. In addition, it could be concluded that there is no significant correlation between the adhesion abilities of probiotics and their role in ameliorating UC, which further illustrated that the adhesion properties of probiotics in vitro may not be suitable as the key criterion for screening potential strains with UC-alleviating effects.

In Vitro Evaluation of Potential Probiotic Strain Lactococcus lactis Gh1 and Its Bacteriocin-Like Inhibitory Substances for Potential Use in the Food Industry

Determination of a microbial strain for the joining into sustenance items requires both in vitro and in vivo assessment. A newly isolated bacteriocin-like inhibitory substance (BLIS) producing lactic acid bacterium, Lactococcus lactis Gh1, was isolated from a traditional flavour enhancer and evaluated in vitro for its potential applications in the food industry. Results from this study showed that L. lactis was tolerant to NaCl (≤ 4.0%, w/v), phenol (≤ 0.4%, w/v), 0.3% (w/v) bile salt, and pH 3. BLIS from L. lactis showed antimicrobial activity against Listeria monocytogenes ATCC 15313 and was susceptible to 10 types of antibiotics. The absence of haemolytic activity and the presence of acid phosphatase and naphthol-AS-BI-phosphohydrolase were observed in L. lactis. L. lactis could coagulate milk and showed a negative response to amylolytic and proteolytic activities and did not secrete β-galactosidase. The antimicrobial activity of BLIS was completely abolished at 121 °C. The BLIS was conserved at 4 °C in BHI and MRS medium up to 6-4 months, respectively. BLIS activity was more stable in BHI as compared to MRS after four freeze-thaw cycles and was not affected by a wide range of pH (pH 4-8). BLIS was sensitive to proteinase k and resistant to catalase and trypsin. The antimicrobial activity was slightly reduced by acetone, ethanol, methanol, and acetonitrile at 10% (v/v) and also towards Tween-80, urea, and NaCl 1% (v/v). Results from this study have demonstrated that L. lactis has a vast potential to be applied in the food industry, such as for the preparation of starter culture, functional foods, and probiotic products.

Bacteriocins, Antimicrobial Peptides from Bacterial Origin: Overview of Their Biology and Their Impact against Multidrug-Resistant Bacteria

Currently, the emergence and ongoing dissemination of antimicrobial resistance among bacteria are critical health and economic issue, leading to increased rates of morbidity and mortality related to bacterial infections. Research and development for new antimicrobial agents is currently needed to overcome this problem. Among the different approaches studied, bacteriocins seem to be a promising possibility. These molecules are peptides naturally synthesized by ribosomes, produced by both Gram-positive bacteria (GPB) and Gram-negative bacteria (GNB), which will allow these bacteriocin producers to survive in highly competitive polymicrobial environment. Bacteriocins exhibit antimicrobial activity with variable spectrum depending on the peptide, which may target several bacteria. Already used in some areas such as agro-food, bacteriocins may be considered as interesting candidates for further development as antimicrobial agents used in health contexts, particularly considering the issue of antimicrobial resistance. The aim of this review is to present an updated global report on the biology of bacteriocins produced by GPB and GNB, as well as their antibacterial activity against relevant bacterial pathogens, and especially against multidrug-resistant bacteria.

Antimicrobial Susceptibility and Antibacterial Mechanism of Limonene against Listeria monocytogenes

Limonene is a monoterpenoid compound, which is founded in a lot of plants’ essential oils with good antibacterial activity against food-borne pathogens, but it has an ambiguous antimicrobial susceptibility and mechanism against Listeria monocytogenes (L. monocytogenes). In this study, the antimicrobial susceptibility of Limonene to L. monocytogenes was studied, and some new sights regarding its antibacterial mechanism were further explored. Scanning electron microscopy (SEM) verified that limonene caused the destruction of the cell integrity and wall structure of L. monocytogenes. The increase in conductivity and the leakage of intracellular biomacromolecules (nucleic acids and proteins) confirmed that limonene had an obvious effect on cell membrane permeability. The results of Propidium Iodide (PI) fluorescence staining were consistent with the results of the conductivity measurements. This indicated that limonene treatment caused damage to the L. monocytogenes cell membrane. Furthermore, the decrease in ATP content, ATPase (Na⁺K⁺-ATPase, Ca²⁺-ATPase) activity and respiratory chain complex activity indicated that limonene could hinder ATP synthesis by inhibiting the activity of the respiratory complex and ATPase. Finally, differential expression of proteins in the respiratory chain confirmed that limonene affected respiration and energy metabolism by inhibiting the function of the respiratory chain complex.

Purification, characterization and mode of action of enterocin, a novel bacteriocin produced by Enterococcus faecium TJUQ1

Enterococcus faecium TJUQ1 with high bacteriocin-producing ability was isolated from pickled Chinese celery. In this study, enterocin TJUQ1 was purified by ammonium sulfate precipitation, reversed-phase chromatography (Sep-Pak C₈) and cation-exchange chromatography. The activity of the purified bacteriocin was 44,566.41 ± 874.69 AU/mg, which corresponds to a purification fold of 35.89 ± 2.34. The molecular mass was 5520 Da by MALDI-TOF MS and Tris-Tricine SDS-PAGE. The result of LC-MS/MS showed that the bacteriocin shared 59.15% identity with enterocin produced by E. faecium GN (accession no. O34071). PCR amplification revealed that E. faecium TJUQ1 possesses a gene encoding enterocin B with 60% identity to enterocin B. Circular dichroism (CD) spectroscopy showed that the molecular conformation was 32.6% helix, 19.5% beta, 12.9% turn and 35.0% random. The stability of enterocin TJUQ1 was measured. After exposure at 121 °C for 15 min, the residual antimicrobial activity of enterocin TJUQ1 was 85.95 ± 1.32%. The antimicrobial activity of enterocin TJUQ1 was still active over a pH range of 3-11. Enterocin TJUQ1 was inactivated after exposure to proteolytic enzymes but was not inactivated by lipase or amylase. These results showed that enterocin TJUQ1 was a novel class II bacteriocin. Enterocin TJUQ1 showed wide antibacterial activity against food-borne gram-negative and gram-positive pathogens, such as Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella enterica. The MIC was 5.26 ± 0.24 μg/mL against L. monocytogenes CMCC 1595. SEM and TEM were used to observe the changes in the morphological and intracellular organization of L. monocytogenes CMCC 1595 cells treated with enterocin TJUQ1. The results demonstrated that enterocin TJUQ1 increased extracellular electrical conductivity, facilitated pore formation, triggered the release of UV-absorbing materials, ATP and LDH, and even caused cell lysis in L. monocytogenes CMCC 1595 cells. Based on the characterization, the wide inhibitory spectrum and mode of action determined so far, enterocin TJUQ1 is a potential preservative for the food industry.

Purification and Partial Characterization of Bacteriocin Lac-B23, a Novel Bacteriocin Production by Lactobacillus plantarum J23, Isolated From Chinese Traditional Fermented Milk

The exploration and evaluation of bacteriocin-producing lactic acid bacteria (LAB) have been one of the powerful means to food preservation. A total of 300 strains were isolated from Chinese traditional fermented milk products. A bacteriocin-producing LAB, named Lactobacillus plantarum J23, was screened and identified. Bacteriocin Lac-B23 from L. plantarum J23 was purified by 80% ammonium sulfate precipitation, cation-exchange chromatography, and reverse-phase high-performance liquid chromatography. Molecular weight of bacteriocin Lac-B23 was determined to be approximately 6.73 kDa by tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, and it was confirmed as a novel bacteriocin by liquid chromatography-mass spectrometry. Moreover, bacteriocin Lac-B23 showed thermal stability when heated at below 100°C for 30 min, pH stability between pH 2.0 and 12.0, and sensitivity to trypsin, proteinase K, and proteinase E. The antimicrobial activity of bacteriocin could be enhanced by addition of Fe²⁺, Mn²⁺, and ethyl alcohol, and inhibited by Cu²⁺, K⁺, Ca²⁺, Zn²⁺, Mg²⁺, and sodium chloride. The results suggested bacteriocin Lac-B23 to have potential application prospects in the food industry.

Isolation, Molecular Characterization and Probiotic Potential of Lactic Acid Bacteria in Saudi Raw and Fermented Milk

Probiotic bacteria can confer health benefits to the human gastrointestinal tract. Lactic acid bacteria (LAB) are candidate probiotic bacteria that are widely distributed in nature and can be used in the food industry. The objective of this study is to isolate and characterize LAB present in raw and fermented milk in Saudi Arabia. Ninety-three suspected LAB were isolated from thirteen different types of raw and fermented milk from indigenous animals in Saudi Arabia. The identification of forty-six selected LAB strains and their genetic relatedness was performed based on 16S rDNA gene sequence comparisons. None of the strains exhibited resistance to clinically relevant antibiotics or had any undesirable hemolytic activity, but they differed in their other probiotic characteristics, that is, tolerance to acidic pH, resistance to bile, and antibacterial activity. In conclusion, the isolates Lactobacillus casei MSJ1, Lactobacillus casei Dwan5, Lactobacillus plantarum EyLan2, and Enterococcus faecium Gail-BawZir8 are most likely the best with probiotic potentials. We speculate that studying the synergistic effects of bacterial combinations might result in a more effective probiotic potential. We suspect that raw and fermented milk products from animals in Saudi Arabia, especially Laban made from camel milk, are rich in LAB and have promising probiotic potential.

Efficient Exploitation of Multiple Novel Bacteriocins by Combination of Complete Genome and Peptidome

Backgroud: The growing emergence of antibiotic-resistant pathogens including the most dangerous superbugs requires quick discovery of novel antibiotics/biopreservatives for human health and food safety. Bacteriocins, a subgroup of antimicrobial peptides, have been considered as promising alternatives to antibiotics. Abundant novel bacteriocins are stored in genome sequences of lactic acid bacteria. However, discovery of novel bacteriocins still mainly relies on dubious traditional purification with low efficiency. Moreover, sequence alignment is invalid for novel bacteriocins which have no homology to known bacteriocins in databases. Therefore, an efficient, simple, universal, and time-saving method was needed to discover novel bacteriocins. Methods and Results: Crude bacteriocins from both cell-related and culture supernatant of Lactobacillus crustorum MN047 fermentation were applied to LC-MS/MS for peptidome assay, by which 131 extracellular peptides or proteins were identified in the complete genome sequence of L. crustorum MN047. Further, the genes of suspected bacteriocins were verified by expressed in Escherichia coli BL21 (DE3) pLysS. Thereafter, eight novel bacteriocins and two nonribosomal antimicrobial peptides were identified to be broad-spectrum activity against both Gram-positive and Gram-negative bacteria, including some multidrug-resistant strains. Among them, BM1556 located within predicted bacteriocin gene cluster. The most active bacteriocin BM1122 had low MIC values of 13.7 mg/L against both Staphylococcus aureus ATCC29213 and E. coli ATCC25922. The BM1122 had bactericidal action mode by biofilm-destruction, pore-formation, and membrane permeability change. Conclusions: The combination of complete genome and peptidome is a valid approach for quick discovery of novel bacteriocins without/with-low homology to known ones. This method will contribute to deep exploitation of novel bacteriocins in genome of bacteria submitted to GenBank.

Purification, Characterization, and Mode of Action of Plantaricin GZ1-27, a Novel Bacteriocin against Bacillus cereus

Bacillus cereus is an opportunistic pathogen that causes foodborne diseases. We isolated a novel bacteriocin, designated plantaricin GZ1-27, and elucidated its mode of action against B. cereus. Plantaricin GZ1-27 was purified using ammonium sulfate precipitation, gel-filtration chromatography, and RP-HPLC. MALDI-TOF/MS revealed that its molecular mass was 975 Da, and Q-TOF-MS/MS analysis predicted the amino acid sequence as VSGPAGPPGTH. Plantaricin GZ1-27 showed thermostability and pH stability. The antibacterial mechanism was investigated using flow cytometry, confocal laser-scanning microscopy, scanning and transmission electron microscopy, and RT-PCR, which revealed that GZ1-27 increased cell membrane permeability, triggered K⁺ leakage and pore formation, damaged cell membrane integrity, altered cell morphology and intracellular organization, and reduced the expression of genes related to cytotoxin production, peptidoglycan synthesis, and cell division. These results suggest that plantaricin GZ1-27 effectively inhibits B. cereus at both the cellular and the molecular levels and is a potential natural food preservative targeting B. cereus.