Plantaricin NC8 from Lactobacillus plantarum causes cell membrane disruption to Micrococcus luteus without targeting lipid II

Mechanism of Cell-Killing Activity of Plantaricin LD1 Against Escherichia coli ATCC 25922

Plantaricin LD1 was purified from a potential probiotic strain, Lactobacillus plantarum LD1 previously isolated from indigenous food, Dosa. In this study, we have performed a detailed mechanism of action of plantaricin LD1 against Escherichia coli ATCC 25922 considering Micrococcus luteus MTCC 106 as control. The plantaricin LD1 showed a minimum inhibitory concentration (MIC) of 34.57 µg/mL and a minimum bactericidal concentration (MBC) of 138.3 µg/mL against M. luteus MTCC 106, whereas MIC 69.15 µg/mL and MBC 276.6 µg/mL were found against E. coli ATCC 25922. The efflux of potassium ions, dissipation of membrane potential (∆ψ), and transmembrane pH gradient (∆pH) of plantaricin LD1-treated cells suggested the membrane-acting nature of plantaricin LD1. Plantaricin LD1 also caused degradation of the genomic DNA of the target strains tested. The cell killing was confirmed by staining with propidium iodide and visualized under light and electron microscopes. The bacteriocin-treated cells were found to be ruptured, swollen, and elongated. Thus, the findings indicate plantaricin LD1 kills E. coli ATCC 25922 by interacting with the cell membrane resulting in the efflux of intracellular contents and also causing degradation of nucleic acids leading to cell death.

Investigating the antidiabetic efficacy of dairy-derived Lacticaseibacillus paracasei probiotic strains: modulating α-amylase and α-glucosidase enzyme functions

The current study aims to evaluate and characterize the probiotic andantidiabetic properties of lactic acid bacteria (LAB) obtained from milk and other dairy-based products. The strains were tested physiologically, biochemically, and molecularly. Based on biochemical tests and 16S rRNA gene amplification and sequencing, all three isolates RAMULAB18, RAMULAB19, and RAMULAB53 were identified as Lacticaseibacillus paracasei with homology similarity of more than 98%. The inhibitory potential of each isolate against carbohydrate hydrolysis enzymes (α-amylase and α-glucosidase) was assessed using three different preparations of RAMULAB (RL) isolates: the supernatant (RL-CS), intact cells (RL-IC), and cell-free extraction (RL-CE). Additionally, the isolate was evaluated for its antioxidant activity against free radicals (DPPH and ABTS). The strain's RL-CS, RL-CE, and RL-IC inhibited α-amylase (17.25 to 55.42%), α-glucosidase (15.08-59.55%), DPPH (56.42-87.45%), and ABTS (46.35-78.45%) enzymes differently. With the highest survival rate (>98%) toward tolerance to gastrointestinal conditions, hydrophobicity (>42.18%), aggregation (>74.21%), as well as attachment to an individual's colorectal cancer cell line (HT-29) (>64.98%), human buccal and chicken crop epithelial cells, all three isolates exhibited extensive results. All three isolates exhibited high resistance toward antibiotics (methicillin, kanamycin, cefixime, and vancomycin), and other assays such as antibacterial, DNase, hemolytic, and gelatinase were performed for safety assessment. Results suggest that the LAB described are valuable candidates for their significant health benefits and that they can also be utilized as a beginning or bio-preservative tradition in the food, agriculture, and pharmaceutical sectors. The LAB isolates are excellent in vitro probiotic applicants and yet additional in vivo testing is required.

Assessment of Polydopamine to Reduce Streptococcus mutans Adhesion to a Dental Polymer

Bacterial adhesion to the surface of materials is the first step in biofilm formation, which will lead to conditions that may compromise the health status of patients. Recently, polydopamine (PDA) has been proposed as an antibacterial material. Therefore, the objective of the current work was to assess and compare the adhesion of Streptococcus mutans to the surface of poly(methyl methacrylate) (PMMA) discs that were modified using PDA following a biomimetic approach versus smooth PDA-coated PMMA surfaces. In addition, an assessment of the growth inhibition by PDA was performed. PMMA discs were manufactured and polished; soft lithography, using the topography from the Crocosmia aurea leaf, was used to modify their surface. PDA was used to smooth-coat PMMA discs by dip-coating. The growth inhibition was measured using an inhibition halo. The surfaces were characterized by means of atomic force microscopy (AFM), the contact angle (CA), and Fourier-transform infrared spectroscopy (FTIR). Polydopamine exhibited a significant antibacterial effect when used directly on the S. mutans planktonic cells, but such an effect was not as strong when modifying the PMMA surfaces. These results open the possibility of using polydopamine to reduce the adhesion and growth of S. mutans, which might have important consequences in the dental field.

A Novel Two-Component Bacteriocin, Acidicin P, and Its Key Residues for Inhibiting Listeria monocytogenes by Targeting the Cell Membrane

Listeria monocytogenes is an important pathogen which easily contaminates food and causes fatal systemic infections in human. Bacteriocins have received much attention regarding their natural methods of controlling health-related pathogens. Here, we investigated and characterized a novel two-component bacteriocin named acidicin P from Pediococcus acidilactici LAC5-17. Acidicin P showed obvious antimicrobial activity to L. monocytogenes. Through a sequence similarity network analysis for two-component bacteriocin precursors mined in the RefSeq database, acidicin P was observed to belong to an unusual group of two-component bacteriocins. Acidicin P contains two peptides designated Adpα and Adpβ which are assessed to interact with each other and form a helical dimer structure which can be inserted into the lipid bilayer of target cell membrane. We demonstrate that A5, N7, and G9 in the A5xxxG9 motif of Adpα and S16, R19, and G20 in the S16xxxG20 motif of Adpβ played crucial roles in stabilizing the helix-helix interaction of Adpα and Adpβ and were essential for the antilisterial activity of acidicin P by site-directed mutagenesis. A positive residue, R14, in Adpα and a negative residue, D12, in Adpβ are also important for acidicin P to fight against L. monocytogenes. These key residues are supposed to form hydrogen bonding, which is crucial for the interaction of Adpα and Adpβ. Furthermore, acidicin P induces severe permeabilization and depolarization of the cytoplasmic membrane and causes dramatic changes in L. monocytogenes cell morphology and ultrastructure. Acidicin P has the potential to be applied to inhibit L. monocytogenes efficiently both in the food industry and medical treatments. IMPORTANCE L. monocytogenes can cause widespread food contamination and severe human listeriosis, which amount to a large proportion of the public health and economic burdens. Today, L. monocytogenes is usually treated with chemical compounds in the food industry or antibiotics for human listeriosis. Natural and safe antilisterial agents are urgently required. Bacteriocins are natural antimicrobial peptides that have comparable narrow antimicrobial spectra and are attractive potentials for precision therapy for pathogen infection. In this work, we discover a novel two-component bacteriocin designated acidicin P, which shows obvious antilisterial activity. We also identify the key residues in both peptides of acidicin P and demonstrate that acidicin P is inserted into the target cell membrane and disrupts the cell envelop to inhibit the growth of L. monocytogenes. We believe that acidicin P is a promising lead for further development as an antilisterial drug.

Factors associated with treatment failure, and possible applications of probiotic bacteria in the arsenal against Helicobacter pylori

INTRODUCTION

Helicobacter pylori is a widespread helical Gram-negative bacterium, which causes a variety of stomach disorders, such as peptic ulcer, chronic atrophic gastritis, and gastric cancer. This microbe frequently colonizes the mucosal layer of the human stomach and survives in the inhospitable microenvironment, by adapting to this hostile milieu.

AREAS COVERED

In this extensive review, we describe conventional antibiotic treatment regimens used against H. pylori including, empirical, tailored, and salvage therapies. Then, we present state-of-the-art information about reasons for treatment failure against H. pylori. Afterward, the latest advances in the use of probiotic bacteria against H. pylori infection are discussed. Finally, we propose a polymeric bio-platform to provide efficient delivery of probiotics for H. pylori infection.

EXPERT OPINION

For effective probiotic delivery systems, it is necessary to avoid the early release of probiotics at the acidic stomach pH, to protect them against enzymes and antimicrobials, and precisely target H. pylori bacteria which have colonized the antrum area of the stomach (basic pH).

Antidiabetic Activity of Potential Probiotics Limosilactobacillus spp., Levilactobacillus spp., and Lacticaseibacillus spp. Isolated from Fermented Sugarcane Juice: A Comprehensive In Vitro and In Silico Study

Probiotics are regarded as a potential source of functional foods for improving the microbiota in human gut. When consumed, these bacteria can control the metabolism of biomolecules, which has numerous positive effects on health. Our objective was to identify a probiotic putative Lactobacillus spp. from fermented sugarcane juice that can prevent α-glucosidase and α-amylase from hydrolyzing carbohydrates. Isolates from fermented sugarcane juice were subjected to biochemical, molecular characterization (16S rRNA) and assessed for probiotic traits. Cell-free supernatant (CS) and extract (CE) and also intact cells (IC) were examined for the inhibitory effect on α-glucosidase and α-amylase. CS of the strain showed the highest inhibition and was subjected to a liquid chromatography-mass spectrometry (LCMS) analysis to determine the organic acid profile. The in silico approach was employed to assess organic acid stability and comprehend enzyme inhibitors' impact. Nine isolates were retained for further investigation based on the preliminary biochemical evaluation. Limosilactobacillus spp., Levilactobacillus spp., and Lacticaseibacillus spp. were identified based on similarity > 95% in homology search (NCBI database). The strains had a higher survival rate (>98%) than gastric and intestinal fluids, also a high capacity for adhesion (hydrophobicity > 56%; aggregation > 80%; HT-29 cells > 54%; buccal epithelial cells > 54%). The hemolytic assay indicated that the isolates could be considered safe. The isolates' derivatives inhibited enzymes to varying degrees, with α-glucosidase inhibition ranging from 21 to 85% and α-amylase inhibition from 18 to 75%, respectively. The CS of RAMULAB54 was profiled for organic acid that showed the abundance of hydroxycitric acid, citric acid, and lactic acid indicating their role in the observed inhibitory effects. The in silico approach has led us to understand that hydroxycitric acid has the ability to inhibit both the enzymes (α-glucosidase and α-amylase) effectively. Inhibiting these enzymes helps moderate postprandial hyperglycemia and regulates blood glucose levels. Due to their promising antidiabetic potential, these isolates can be used to enhance intestinal health.

Isolation and characterization of lactic acid bacteria with potential probiotic activity and further investigation of their activity by α-amylase and α-glucosidase inhibitions of fermented batters

Probiotic microbiota plays a vital role in gastrointestinal health and possesses other beneficial attributes such as antimicrobial and antibiotic agents along with a significant role in the management of diabetes. The present study identifies the probiotic potential of Lactobacillus spp. isolated from three traditionally fermented foods namely, jalebi, medhu vada, and kallappam batters at biochemical, physiological, and molecular levels. By 16S rRNA gene amplification and sequencing, the isolates were identified. A similarity of >98% to Lacticaseibacillus rhamnosus RAMULAB13, Lactiplantibacillus plantarum RAMULAB14, Lactiplantibacillus pentosus RAMULAB15, Lacticaseibacillus paracasei RAMULAB16, Lacticaseibacillus casei RAMULAB17, Lacticaseibacillus casei RAMULAB20, and Lacticaseibacillus paracasei RAMULAB21 was suggested when searched for homology using NCBI database. Utilizing the cell-free supernatant (CS), intact cells (IC), and cell-free extract (CE) of the isolates, inhibitory potential activity against the carbohydrate hydrolyzing enzymes α-glucosidase and α-amylase was assessed. CS, CE, and IC of the isolates had a varying capability of inhibition against α-glucosidase (15.08 to 59.55%) and α-amylase (18.79 to 63.42%) enzymes. To assess the probiotic potential of seven isolates, various preliminary characteristics were examined. All the isolates exhibited substantial tolerance toward gastrointestinal conditions and also demonstrated the highest survival rate (> 99%), hydrophobicity (> 65%), aggregation (> 76%), adherence to HT-29 cells (> 84%), and chicken crop epithelial cells suggesting that the isolates had a high probiotic attribute. Additionally, the strains showed remarkable results in safety assessment assays (DNase and hemolytic), and antibacterial and antibiotic evaluations. The study concludes that the lactic acid bacteria (LAB) characterized possesses outstanding probiotic properties and has antidiabetic effects. In order to obtain various health advantages, LAB can be utilized as probiotic supplements.

A Class IIb Bacteriocin Plantaricin NC8 Modulates Gut Microbiota of Different Enterotypes in vitro

The gut microbiota is engaged in multiple interactions affecting host health. Bacteriocins showed the ability of impeding the growth of intestinal pathogenic bacteria and modulating gut microbiota in animals. Few studies have also discovered their regulation on human intestinal flora using an in vitro simulated system. However, little is known about their effect on gut microbiota of different enterotypes of human. This work evaluated the modification of the gut microbiota of two enterotypes (ET B and ET P) by the class IIb bacteriocin plantaricin NC8 (PLNC8) by using an in vitro fermentation model of the intestine. Gas chromatography results revealed that PLNC8 had no influence on the gut microbiota’s production of short-chain fatty acids in the subjects’ samples. PLNC8 lowered the Shannon index of ET B’ gut microbiota and the Simpson index of ET P’ gut microbiota, according to 16S rDNA sequencing. In ET B, PLNC8 enhanced the abundance of Bacteroides, Bifidobacterium, Megamonas, Escherichia-Shigella, Parabacteroides, and Lactobacillus while decreasing the abundance of Streptococcus. Prevotella_9, Bifidobacterium, Escherichia-Shigella, Mitsuokella, and Collinsella were found more abundant in ET P. The current study adds to our understanding of the impact of PLNC8 on the human gut microbiota and lays the groundwork for future research into PLNC8’s effects on human intestinal disease.

Evaluation of Probiotic and Antidiabetic Attributes of Lactobacillus Strains Isolated From Fermented Beetroot

Fermented foods are sources of functionally salient microbes. These microbes when ingested can regulate biomolecule metabolism which has a plethora of health benefits. Lactic acid bacteria species (LABs) isolated from fermented beetroot were biochemically characterized and validated using 16s rRNA sequence. Also, an in vitro assay was conducted to confirm the probiotic activity of the isolates. The cell-free supernatant (CS), cell-free extract (CE), and intact cell (IC) were evaluated for α-glucosidase and α-amylase inhibition. The six isolates RAMULAB01–06 were categorized to be Lactobacillus spp. by observing phenotypic and biochemical characters. Molecular validation using 16S rDNA sequencing, followed by homology search in NCBI database, suggested that the isolates are >95% similar to L. paracasei and L. casei. Also, isolates exhibited probiotic potential with a high survival rate (>96%) in the gastrointestinal condition, and adherence capability (>53%), colonization (>86%), antibacterial, and antibiotic activity. The safety assessments expressed that the isolates are safe. The α-glucosidase and α-amylase inhibition by CS, CE, and IC ranged from 3.97 ± 1.42% to 53.91 ± 3.11% and 5.1 ± 0.08% to 57.15 ± 0.56%, respectively. Hence, these species have exceptional antidiabetic potential which could be explicated to its use as a functional food and health-related food products.

K. J, S. JC, Ramu R. Probiotic Potential Lacticaseibacillus casei and Limosilactobacillus fermentum Strains Isolated from Dosa Batter Inhibit α-Glucosidase and α-Amylase Enzymes

Fermented food plays a major role in gastrointestinal health, as well as possesses other health benefits, such as beneficiary effects in the management of diabetes. Probiotics are thought to be viable sources for enhancing the microbiome of the human gut. In the present study, using biochemical, physiological, and molecular approaches, the isolated Lactobacillus spp. from dosa batter were identified. The cell-free supernatant (CS), cell-free extract (CE), and intact cells (IC) were evaluated for their inhibitory potential against the carbohydrate hydrolyzing enzymes α-glucosidase and α-amylase. Then, 16S rDNA amplification and sequencing were used to identify the species. A homology search in NCBI database was performed that suggests the isolates are >95% similar to Limosilactobacillus fermentum and Lacticaseibacillus casei. Different standard parameters were used to evaluate the probiotic potential of strains RAMULAB07, RAMULAB08, RAMULAB09, RAMULAB10, RAMULAB11, and RAMULAB12. The strains expressed a significant tolerance to the gastric and intestinal juices with a higher survival rate (>98%). A high adhesion capability was observed by the isolates exhibited through hydrophobicity (>65%), aggregation assays (>75%), and adherence assay on HT-29 cells (>82%) and buccal epithelial cells. In addition, the isolates expressed antibacterial and antibiotic properties. Safety assessments (DNase and hemolytic assay) revealed that the isolates could be classified as safe. α-glucosidase and α-amylase inhibition of the isolates for CS, CE, and IC ranged from 7.50% to 65.01% and 20.21% to 56.91%, respectively. The results suggest that these species have exceptional antidiabetic potential, which may be explained by their use as foods that can have health-enhancing effects beyond basic nutrition.

Use of Lactiplantibacillus plantarum ZJ316 as a starter culture for nitrite degradation, foodborne pathogens inhibition and microbial community modulation in pickled mustard fermentation

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L. plantarum ZJ316 (ZJ316) was used as a starter for pickled mustard fermentation.

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ZJ316 inoculation could reduce the nitrite content of pickled mustard.

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The pickled mustard inoculated with ZJ316 exhibited more volatile components.

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ZJ316 could modulate the microbial community during pickled mustard fermentation

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ZJ316 as a starter could inhibit the growth of pathogenic bacteria.

The potential of Lactiplantibacillus plantarum ZJ316 (ZJ316) as a starter culture for quality improvement and microbial community regulation in pickled mustard fermentation was elucidated in this study. Our results show that ZJ316 can deter the occurrence of nitrite peaks and maintain the nitrite content of pickled mustard at a low level (0.34 mg/kg). The headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry results indicate that ZJ316 gives a good flavor to pickled mustard. According to the 16S rDNA results, Firmicutes were the predominant microbiota after inoculation with ZJ316, and the abundances of Citrobacter, Enterobacter, and Proteus decreased simultaneously. In addition, antibacterial activity analysis showed that the supernatant of pickled mustard inoculated with ZJ316 had a significant inhibitory effect on Staphylococcus aureus D48, Escherichia coli DH5α, and Listeria monocytogenes LM1. In conclusion, L. plantarum ZJ316 has potential for use as an ideal starter in the process of vegetable fermentation.

Antibacterial Effects of Bacteriocin PLNC8 against Helicobacter pylori and Its Potential Mechanism of Action

Helicobacter pylori (H. pylori) is a bacterium that can cause a variety of gastric diseases. Most bacteriocins have gained popularity due to their non-toxic effects on cells and antibacterial effects against a wide range of pathogenic bacteria. In this study, the chemical synthesis of the bipeptide bacteriocin PLNC8 was used to investigate its possible action mechanism against H. pylori ZJC03 in vitro. Results showed that PLNC8 had significant anti-H. pylori ZJC03 potential, which resulted in a significant reduction in urease activity and a minimum inhibitory concentration (MIC) of 80 μM. PLNC8 inhibited the growth of H. pylori ZJC03, disrupting its structure as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, PLNC8 decreased the ATP level and hydrogen peroxide sensitivity of H. pylori ZJC03. In conclusion, PLNC8 disrupts the ability of H. pylori ZJC03 to alter the host environment, providing a new avenue for the prevention and control of H. pylori infection, providing a theoretical foundation for further elucidation of its regulatory mechanism.

Bioprospecting Antimicrobials from Lactiplantibacillus plantarum: Key Factors Underlying Its Probiotic Action

Lactiplantibacillus plantarum (L. plantarum) is a well-studied and versatile species of lactobacilli. It is found in several niches, including human mucosal surfaces, and it is largely employed in the food industry and boasts a millenary tradition of safe use, sharing a long-lasting relationship with humans. L. plantarum is generally recognised as safe and exhibits a strong probiotic character, so that several strains are commercialised as health-promoting supplements and functional food products. For these reasons, L. plantarum represents a valuable model to gain insight into the nature and mechanisms of antimicrobials as key factors underlying the probiotic action of health-promoting microbes. Probiotic antimicrobials can inhibit the growth of pathogens in the gut ensuring the intestinal homeostasis and contributing to the host health. Furthermore, they may be attractive alternatives to conventional antibiotics, holding potential in several biomedical applications. The aim of this review is to investigate the most relevant papers published in the last ten years, bioprospecting the antimicrobial activity of characterised probiotic L. plantarum strains. Specifically, it focuses on the different chemical nature, the action spectra and the mechanisms underlying the bioactivity of their antibacterial and antiviral agents. Emerging trends in postbiotics, some in vivo applications of L. plantarum antimicrobials, including strengths and limitations of their therapeutic potential, are addressed and discussed.

Lactiplantibacillus plantarum-Nomad and Ideal Probiotic

Probiotics are increasingly recognized as capable of positively modulating several aspects of human health. There are numerous attributes that make an ideal probiotic. Lactiplantibacillus plantarum (Lp) exhibits an ecological and metabolic flexibility that allows it to thrive in a variety of environments. The present review will highlight the genetic and functional characteristics of Lp that make it an ideal probiotic and summarizes the current knowledge about its potential application as a prophylactic or therapeutic intervention.

A Novel Bacteriocin From Lactobacillus Pentosus ZFM94 and Its Antibacterial Mode of Action

Bacteriocins are bioactive antimicrobial peptides synthesized in the ribosome of numerous bacteria and released extracellularly. Pentocin ZFM94 produced by Lactobacillus pentosus (L. pentosus) ZFM94, isolated from infant feces with strong antibacterial activity, was purified by ammonium sulfate precipitation, dextran gel chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). The molecular mass of the purified bacteriocin was 3,547.74 Da determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Pentocin ZFM94 exhibited broad-spectrum antimicrobial activity against tested Gram-positive and Gram-negative bacteria, and the minimal inhibitory concentrations (MICs) of Micrococcus luteus (M. luteus) 10,209, Staphylococcus aureus (S. aureus) D48, and Escherichia coli (E. coli) DH5α were 1.75, 2.00, and 2.50 μm, respectively. Pentocin ZFM94 was heat-stable (30 min at 80°C) and showed inhibitory activity over a wide pH range (5.00–7.00). It could be degraded by trypsin and pepsin, but not by amylase, lysozyme, lipase, and ribonuclease A. Fluorescence leakage assay showed that pentocin ZFM94 induced disruption of the cell membrane and caused leakage of cellular content. Furthermore, lipid II was not an antibacterial target of pentocin ZFM94. This study laid the foundation for further development and utilization of L. pentosus ZFM94 and its bacteriocin.

Evaluation of the membrane damage mechanism of protocatechualdehyde against Yersinia enterocolitica and simulation of growth inhibition in pork

This study sought to explore the antibacterial mechanism associated with membrane damage in Yersinia enterocolitica by protocatechualdehyde (PCA), thus providing improved knowledge of whether PCA is suitable for pork preservation. The minimum inhibitory concentration (MIC) of PCA was determined by micro-broth dilution. We then characterized functional and morphological changes of Y. enterocolitica treated with PCA. Finally, the growth inhibition model of PCA against Y. enterocolitica in pork was established using the response surface method. Accordingly, the MIC of PCA against Y. enterocolitica was found to be 0.3125 mg/mL. Significant observations incorporated membrane depolarization, a markedly decreased intracellular ATP and pH, and morphological changes induced by PCA treatment. After PCA treatment under low temperatures, the average Y. enterocolitica count in pork decreased by two log cycles. According to the obtained findings, PCA exhibited satisfactory performances as a food preservative to control the growth and reproduction of Y. enterocolitica in pork.

Anti-Salmonella mode of action of natural L-phenyl lactic acid purified from Lactobacillus plantarum ZJ316

Salmonella is a serious foodborne pathogen responsible for more than 90 million cases of gastroenteritis worldwide annually. Due to the gradual increase in antibiotic-resistant Salmonella strains, the identification of natural antibacterial substances is urgently needed. Herein, we purified natural L-phenyl lactic acid (L-PLA) from Lactobacillus plantarum ZJ316 and revealed its antimicrobial mode against Salmonella enterica subsp. enterica ATCC 14028. L-PLA (98.14% pure) was obtained using the macroporous resin XAD-16, solid-phase extraction (SPE), reverse-phase high-performance liquid chromatography (RP-HPLC), and chiral chromatography. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the cell morphology was severely compromised. Transmembrane electrical potential (ΔΨ), transmembrane pH gradient (ΔpH), intracellular ATP level, extracellular electrical conductivity (EC), and genomic DNA analyses were employed to evaluate the antibacterial mode of action of L-PLA. The proton motive force (PMF) and ATP of Salmonella cells rapidly dissipated, and the EC markedly increased. The gel retardation assay demonstrated that L-PLA could bind to genomic DNA and intercalate into the nucleic acids. The anti-Salmonella mode of action of L-PLA was attributed to the destruction of the cell membrane and genomic DNA binding. This research suggests that L-PLA has potential applications as an antimicrobial agent in food, medicine, and other fields. KEY POINTS: • Natural L-PLA was purified from L. plantarum ZJ316 with a purity of 98.14%. • L-PLA effectively inhibited Salmonella strains by antibacterial activities and MICs. • Membrane destruction and binding with DNA are the anti-Salmonella modes of L-PLA.

Mini Review on Antimicrobial Peptides, Sources, Mechanism and Recent Applications

Antimicrobial peptides in recent years have gained increased interest among scientists, health professionals and the pharmaceutical companies owing to their therapeutic potential. These are low molecular weight proteins with broad range antimicrobial and immuno modulatory activities against infectious bacteria (Gram positive and Gram negative), viruses and fungi. Inability of micro-organisms to develop resistance against most of the antimicrobial peptide has made them as an efficient product which can greatly impact the new era of antimicrobials. In addition to this these peptides also demonstrates increased efficacy, high specificity, decreased drug interaction, low toxicity, biological diversity and direct attacking properties. Pharmaceutical industries are therefore conducting appropriate clinical trials to develop these peptides as potential therapeutic drugs. More than 60 peptide drugs have already reached the market and several hundreds of novel therapeutic peptides are in preclinical and clinical development. Rational designing can be used further to modify the chemical and physical properties of existing peptides. This mini review will discuss the sources, mechanism and recent therapeutic applications of antimicrobial peptides in treatment of infectious diseases.

Unveiling the potentials of bacteriocin (Pediocin L50) from Pediococcus acidilactici with antagonist spectrum in a Caenorhabditis elegans model

Human-milk-based probiotics play a major role in the early colonization and protection of infants against gastrointestinal infection. We investigated potential probiotics in human milk. Among 41 Lactic acid bacteria (LAB) strains, four strains showed high antimicrobial activity against Escherichia coli 0157:H7, Listeria monocytogenes ATCC 15313, Bacillus cereus ATCC 14576, Staphylococcus aureus ATCC 19095, and Helicobacter pylori. The selected LAB strains were tested in simulated gastrointestinal conditions for their survival. Four LAB strains showed high resistance to pepsin (82%-99%), bile with pancreatine stability (96%-100%), and low pH (80%-94%). They showed moderate cell surface hydrophobicity (22%-46%), auto-aggregation abilities (12%-34%), and 70%-80% co-aggregation abilities against L. monocytogenes ATCC 15313, S. aureus ATCC 19095, B. cereus ATCC 14576, and E. coli 0157:H7. All four selected isolates were resistant to gentamicin, imipenem, novobiocin, tetracycline, clindamycin, meropenem, ampicillin, and penicillin. The results show that Pediococcus acidilatici is likely an efficient probiotic strain to produce < 3 Kda pediocin-based antimicrobial peptides, confirmed by applying amino acid sequences), using liquid chromatography mass spectrometry and HPLC with the corresponding sequences from class 2 bacteriocin, and based on the molecular docking, the mode of action of pediocin was determined on LipoX complex, further the ¹³C nuclear magnetic resonance structural analysis, which confirmed the antimicrobial peptide as pediocin.