A non-pediocin low molecular weight antimicrobial peptide produced by Pediococcus pentosaceus strain IE-3 shows increased activity under reducing environment

Acidocin A and Acidocin 8912 Belong to a Distinct Subfamily of Class II Bacteriocins with a Broad Spectrum of Antimicrobial Activity

Within class II bacteriocins, we assume the presence of a separate subfamily of antimicrobial peptides possessing a broad spectrum of antimicrobial activity. Although these peptides are structurally related to the subclass IIa (pediocin-like) bacteriocins, they have significant differences in biological activities and, probably, a mechanism of their antimicrobial action. A representative of this subfamily is acidocin A from Lactobacillus acidophilus TK9201. We discovered the similarity between acidocin A and acidocin 8912 from Lactobacillus acidophilus TK8912 when analyzing plasmids from lactic acid bacteria and suggested the presence of a single evolutionary predecessor of these peptides. We obtained the C-terminally extended homolog of acidocin 8912, named acidocin 8912A, a possible intermediate form in the evolution of the former. The study of secondary structures and biological activities of these peptides showed their structural similarity to acidocin A; however, the antimicrobial activities of acidocin 8912 and acidocin 8912A were lower than that of acidocin A. In addition, these peptides demonstrated stronger cytotoxic and membranotropic effects. Building upon what we previously discovered about the immunomodulatory properties of acidocin A, we studied its proteolytic stability under conditions simulating those in the digestive tract and also assessed its ability to permeate intestinal epithelium using the Caco-2 cells monolayer model. In addition, we found a pronounced effect of acidocin A against fungi of the genus Candida, which might also expand the therapeutic potential of this bacterial antimicrobial peptide.

Heterologous expression of frog antimicrobial peptide Odorranain-C1 in Pichia pastoris: Biological characteristics and its application in food preservation

To reduce food spoilage and deterioration caused by microbial contamination, antimicrobial peptides (AMPs) have gradually gained attention as a biological preservative. Odorranain-C1 is an α-helical cationic antimicrobial peptide extracted from the skin of frogs with broad-spectrum antimicrobial activity. In this study, we achieved the expression of Odorranain-C1 in Pichia pastoris (P. pastoris) (also known as Komagataella phaffii) by employing DNA recombination technology. The recombinant Odorranain-C1 showed broad-spectrum antibacterial activity and displayed a minimum inhibitory concentration within the range of 8-12 μg.mL-1. Meanwhile, Odorranain-C1 exhibited superior stability and lower hemolytic activity. Mechanistically, Odorranain-C1 disrupted the bacterial membrane's integrity, ultimately causing membrane rupture and subsequent cell death. In tilapia fillets preservation, Odorranain-C1 inhibited the total colony growth and pH variations, while also reducing the production of total volatile basic nitrogen (TVB-N) and thiobarbituric acid (TBA). In conclusion, these studies demonstrated the efficient recombinant expression of Odorranain-C1 in P. pastoris, highlighting its promising utilization in food preservation.

Studies on a new antimicrobial peptide from Vibrio proteolyticus MT110

The marine environment is known for its vast diversity of the microbial population; however, less explored for bioactive compounds. In this study, an AMP produced by a new marine isolate, Vibrio proteolyticus MT110, showed broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria. The AMP was purified to homogeneity using ethyl acetate extraction followed by RP-HPLC, and LC-MS analysis showed its molecular weight as 980 Da. The MIC of AMP (peptide-MT110) was obtained in the 7.81-31.25 µg/mL range against different indicator strains. Peptide-MT110 showed stability of its antimicrobial activity at 15-121 °C and pH 4-10 and in the presence of various hydrolytic enzymes. The peaks at 1536 cm-1 and 1712 cm-1 wavenumbers in FTIR spectra confirmed the peptidic nature of AMP, and its amino acid analysis confirmed the presence of tyrosine and isoleucine. The antibacterial activity of peptide-MT110 is confirmed by PI assay and TEM. The optimization of peptide-MT110 production using statistical methods resulted in a 2.64-fold higher production. The physicochemical properties and stability in wide pH and temperature ranges showed the potential of peptide-MT110 for its development as a drug candidate. This is believed to be the first report on an AMP from Vibrio proteolyticus.

An antimicrobial thiopeptide producing novel actinomycetes Streptomyces terrae sp. nov., isolated from subsurface soil of arable land

An antimicrobial producing Gram-positive, aerobic, nonmotile, and filamentous actinobacterial strain SKN60T was isolated from soil The isolate exhibited 99.3% and 99.0% identity with Streptomyces laurentii ATCC 31255T and S. roseicoloratus TRM 44457T, respectively, in 16S rRNA gene sequence analysis. However, the genome sequence displayed maximum ANI (88.45%) and AAI (85.61%) with S. roseicoloratus TRM 44457T. Similarly, the dDDH showed 33.7% identity with S. roseicoloratus TRM 44457T. It formed a cluster with S. roseicoloratus TRM 44457T and S. laurentii ATCC 31255T in phylogenomic tree. Cell wall analysis revealed the presence of diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylcholine as major polar lipids and diaminopimelic acid as diagnostic diamino acid. Major fatty acids were iso-C15:0, anteiso-C15:0, and iso-C16:0. The G+C content was found to be 72.3 mol%. Genome sequence analysis using antiSMASH database showed occurrence of a thiopeptide biosynthesis gene cluster with 94% similarity to berninamycin from S. bernensis UC5144. The mass of 1146 Da is identical with berninamycin. But subtle differences observed in leader peptide sequence of thiopeptide and berninamycin. Notably, S. bernensis is not validly reported and thus SKN60T is the only strain containing berninamycin BGC as no other phylogenetic relative had it. Additionally, strain SKN60T differed in phenotypic and genetic characteristics with all phylogenetic relatives of the genus Streptomyces. Therefore, it is proposed as a novel species with the name Streptomyces terrae sp. nov. strain SKN60T (=MTCC 13163T; = JCM 35768T).

Antimicrobial Activity of Peptides Produced by Lactococcus lactis subsp. lactis on Swine Pathogens

Swine production is of great importance worldwide and has huge economic and commercial impact. Due to problems with bacterial infection, the use of antimicrobials has increased in the last decades, particularly in Latin America and Asia. This has led to concerns about antimicrobial resistance, which poses risks to human health and the environment. The use of probiotic organisms has been proposed as an alternative to this use, as these beneficial bacteria can produce antimicrobial peptides, such as bacteriocins, which allow the induction of inhibitory effects against pathogenic microorganisms. Among probiotics, some bacteria stand out with the inhibition of animal pathogens. The bacteriocin-like inhibitory substances (BLISs) of Lactococcus lactis subsp. lactis strain L2, present in its cell-free supernatant, were tested against pathogenic strains isolated from pig samples, such as Escherichia coli, Salmonella enterica, Streptococcus suis, Streptococcus dysgalactiae, Staphylococcus hyicus, and Enterococcus faecalis. Compounds secreted by L. lactis L2 have been shown to inhibit the growth of some pathogenic species, particularly Gram-positive bacteria, with S. suis being the most prominent. Antimicrobial peptides with a molecular size of 500-1160 Daltons were isolated from BLISs. The results highlight the potential of L. lactis BLISs and its peptides as natural antimicrobials for use in the food industry and to reduce the use of growth promoters in animal production.

Staphylococcus aureus is able to generate resistance to novel lipoglycopeptide antibiotic gausemycin A

Gausemycin A is the first member of the novel lipoglycopeptides family produced by Streptomyces roseoflavus INA-Ac-5812. Gausemycin A has a pronounced bactericidal activity against methicillin-resistant Staphylococcus aureus. However, the ability of S. aureus to be resistant to gausemycin A has not been investigated yet. Using serial passaging, we have obtained the resistant variant S. aureus 5812R, which is 80 times more resistant compared to the parent strain. Susceptibility testing of S. aureus 5812R revealed the acquisition of cross-resistance to daptomycin, cefazolin, tetracycline, and gentamicin, while the resistance to vancomycin, nisin, and ramoplanin was absent. Whole genome sequencing revealed single nucleotide polymorphism (SNP) and deletions in S. aureus 5812R, among which are genes encoding efflux pump (sepA), the two-component Kdp system (kdpE), and the component of isoprenoid biosynthesis pathway (hepT). Phenotypically, S. aureus 5812R resembles a small-colony variant, as it is slow-growing, forms small colonies, and is deficient in pigments. Profiling of fatty acids (FA) composition constituting the cytoplasmic membrane of S. aureus 5812R revealed the prevalence of anteiso-branched FA, while straight FA was slightly less present. The evidence also showed that the gausemycin A-resistant strain has increased expression of the cls2 gene of the cardiolipin synthase. The performed checkerboard assay pointed out that the combination of gausemycin A and ciprofloxacin showed a synergistic effect against S. aureus 5812R.

Antimicrobial activity, environmental sensitivity, mechanism of action, and food application of αs165-181 peptide

αs165-181 is a peptide derived from αs₂-casein of ovine milk. Herein, we report the antimicrobial activity and mechanism, and food application of the peptide. αs165-181 showed antimicrobial activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Listeria monocytogenes, Bacillus cereus, and Salmonella enterica serovar Enteritidis in a dose-dependent manner. The minimum inhibitory concentration of the peptide was 3.9 mg/ml for E. coli and 7.8 mg/ml for the other bacteria. The peptide did not show antimicrobial activity against Lactobacillus plantarum up to 3.9 mg/ml concentration. The minimum bactericidal concentration of αs165-181 peptide was 7.8 mg/ml for E. coli, S. aureus, L. monocytogenes, and B. cereus. The peptide was sensitive to monovalent and divalent cations, pH, and high temperatures. Transmission electron microscopy, cytoplasmic β-galactosidase leakage, and DNA electrophoresis analyses showed that αs165-181 peptide affects bacteria by damaging cell membrane and binding to the genomic DNA. When αs165-181 peptide was applied to minced beef or UHT cream, the antimicrobial activity (7.8 mg/g) was almost the same as or even better than nisin (0.5 mg/g). This study helps understand the antimicrobial mode of action of αs165-181 peptide and develop strategies for application in food products.

Probiotic Potential and Gluten Hydrolysis Activity of Lactobacillus brevis KT16-2

Celiac disease (CD) is a chronic autoimmune disease that occurs in genetically predisposed individuals. Gluten-hydrolyzing probiotic bacteria are promising for alleviating symptoms in individuals with CD. Therefore, in this study, the gluten hydrolysis ability and probiotic potential of Lact. brevis KT16-2 were determined. Lact. brevis KT16-2 formed proteolysis zones on gluten and gliadin agar plates, in which gluten and gliadin were used as the only nitrogen sources. SDS-PAGE analysis showed that Lact. brevis KT16-2 completely hydrolyzed peptides ranging from 28 to 66 kDa in 8 h. Then, the survival of the strain in bile salts, in simulated gastric juice and at low pH was determined. Additionally, the antioxidant and antimicrobial substance production, autoaggregation, hydrophobicity and antibiotic resistance of the strain were investigated. API-ZYM test kits were used to determine the enzymatic capacity of the strain. Lact. brevis KT16-2 had the ability to hydrolyze wheat gluten. It was able to survive in a broad pH range (pH 2-8), in bile salts (0.3-1%), and in simulated gastric juice. It had the ability to autoaggregate (59.4%), and the hydrophobicity (52.7%) of the strain was determined. In addition, this strain was capable of producing antimicrobial peptides against test bacteria, including antibiotic-resistant bacteria. Cell-free supernatants (CFS) of the strain had high antioxidant activity (DPPH-71.0% and ABTS-54.1%). The results of this study suggest that Lact. brevis KT16-2, which can hydrolyze gliadin and has many essential probiotic properties, has the potential to be used as a probiotic supplement for individuals with CD.

Bacteriostatic activity and partial characterization of the bacteriocin produced by L. plantarum sp. isolated from traditional sourdough

This study was aimed to isolate and partially characterizes the bacteriocin produced by an L. plantarum sp. isolated from traditional sourdough. The bacteriocin was partially purified, and after treating it with different harsh conditions, its antibacterial activity was evaluated against L. monocytogenes as an indicator. Also, the growth phase during which the bacteriocin is produced, and its mode of action, was examined. Finally, the molecular weight of this compound was evaluated by using SDS-PAGE analysis. According to the results, this bacteriocin had a molecular weight well lower than 10 kDa that was mainly produced at the early stationary phase and reached its highest activity (3,200 AU/ml) at the same stage. It was tolerant toward a wide range of pH (2-10), temperatures (-20 to 120°C), and high concentrations of NaCl. Notably, the bacteriocin-producing strain had proteolytic activity, while the bacteriocin produced by that showed resistance to proteolytic enzymes (pepsin, trypsin, and proteinase K). Also, it was revealed that the bacteriocin activity is mostly bacteriostatic so that it considerably inhibits pathogens' growth, particularly S. aureus, E. coli, and L. monocytogenes. These characteristics prove that strain and its bacteriocin can be considered as one of the most promising agents to use in the food industry.

Surfactin Like Broad Spectrum Antimicrobial Lipopeptide Co-produced With Sublancin From Bacillus subtilis Strain A52: Dual Reservoir of Bioactives

An antimicrobial substance producing strain designated as A52 was isolated from a marine sediment sample and identified as Bacillus sp., based on 16S rRNA gene sequence analysis. The ANI and dDDH analysis of the genome sequence displayed high identity with two strains of B. subtilis sub sp. subtilis. Strain A52 yielded two antimicrobial peptides (AMPs) that differed in activity spectrum. MALDI mass spectrometry analysis of HPLC purified fractions revealed mass of peptides as 3881.6 and 1061.9 Da. The antiSMASH analysis of genome sequence unraveled presence of identical biosynthetic cluster involved in production of sublancin from B. subtilis sub sp. subtilis strain 168, which yielded peptide with identical mass. The low molecular weight peptide is found to be a cyclic lipopeptide containing C₁₆ β-hydroxy fatty acid that resembled surfactin-like group of biosurfactants. However, it differed in fatty acid composition and antimicrobial spectrum in comparison to other surfactins produced by strains of B. subtilis. It exhibited broad spectrum antibacterial activity, inhibited growth of pathogenic strains of Candida and filamentous fungi. Further, it exhibited hemolytic activity, but did not show phytotoxic effect in seed germination experiment. The emulgel formulation of surfactin-like lipopeptide showed antimicrobial activity in vitro and did not show any irritation effects in animal studies using BALB/c mice. Moreover, surfactin-like lipopeptide displayed synergistic activity with fluconazole against Candida, indicating its potential for external therapeutic applications.

Topical antimicrobial peptide formulations for wound healing: Current developments and future prospects

Antimicrobial peptides (AMPs) are the natural antibiotics recognized for their potent antibacterial and wound healing properties. Bare AMPs have limited activity following topical application attributable to their susceptibility to environment (hydrolysis, oxidation, photolysis), and wound (alkaline pH, proteolysis) related factors as well as minimal residence time. Therefore, the formulation of AMPs is essential to enhance stability, prolong delivery, and optimize effectiveness at the wound site. Different topical formulations of AMPs have been developed so far including nanoparticles, hydrogels, creams, ointments, and wafers to aid in controlling bacterial infection and enhance wound healing process in vivo. Herein, an overview is provided of the AMPs and current understanding of their formulations for topical wound healing applications along with suitable examples. Furthermore, future prospects for the development of effective combination AMP formulations are discussed. STATEMENT OF SIGNIFICANCE: Chronic wound infection and subsequent development of antibiotic resistance are serious clinical problems affecting millions of people worldwide. Antimicrobial peptides (AMPs) possess great potential in effectively killing the bacteria with minimal risk of resistance development. However, AMPs susceptibility to degradation following topical application limits their antimicrobial and wound healing effects. Therefore, development of an optimized topical formulation with high peptide stability and sustained AMP delivery is necessary to maximize the antimicrobial and wound healing effects. The present review provides an overview of the state-of-art in the field of topical AMP formulations for wound healing. Current developments in the field of topical AMP formulations are reviewed and future prospects for the development of effective combination AMP formulations are discussed.

Antibacterial Therapeutic Agents Composed of Functional Biological Molecules

Antibacterial agents are a group of materials that selectively destroy bacteria by interfering with bacterial growth or survival. With the emergence of resistance phenomenon of bacterial pathogens to current antibiotics, new drugs are frequently entering into the market along with the existing drugs, and the alternative compounds with antibacterial functions are being explored. Due to the advantages of their inherent biochemical and biophysical properties including precise targeting ability, biocompatibility, biodegradability, long blood circulation time, and low cytotoxicity, biomolecules such as peptides, carbohydrates, and nucleic acids have huge potential for the antimicrobial application and have been extensively studied in recent years. In this review, antimicrobial therapeutic agents composed of three kinds of functional biological molecules were summarized. In addition, the research progress of antibacterial mechanism, chemical modification, and nanoparticle coupling of those biomolecules were also discussed.

Effects of pH and sugar supplements on bacteriocin-like inhibitory substance production by Pediococcus pentosaceus

To improve bacteriocin-like inhibitory substance (BLIS) production by Pediococcus pentosaceus ATCC 43200, the influence of pH as well as the addition of sugars-either prebiotic (inulin) or not (sucrose)-on its metabolism were investigated. This strain was grown at pH 5.0 or 6.0 either in glucose-based MRS medium (control) or after addition of 0.5, 1.0 or 1.5% (w/w) sucrose and inulin (GSI-MRS) in the same percentages. In the control medium at pH 5.0, cell mass concentration after 48 h of fermentation (X_max = 2.26 g/L), maximum specific growth rate (µ_max = 0.180 h^-1) and generation time (T_g = 3.84 h) were statistically coincident with those obtained in supplemented media. At pH 6.0 some variations occurred in these parameters between the control medium (X_max = 2.68 g/L; µ_max = 0.32 h^-1; T_g = 2.17 h) and the above supplemented media (X_max = 1.90, 2.52 and 1.86 g/L; µ_max = 0.26, 0.33 and 0.32 h^-1; T_g = 2.62, 2.06 and 2.11 h, respectively). Lactate production was remarkable at both pH values (13 and 16 g/L) and improved in all supplemented media, being 34 and 54% higher than in their respective control media, regardless of the concentration of these ingredients. Cell-free supernatant of the fermented control medium at pH 5.0 displayed an antimicrobial activity against Enterococcus 101 5.3% higher than that at pH 6.0 and even 20% higher than those of all supplemented media, regardless of the concentration of supplements. BLIS production was favored either at pH 5.0 or in the absence of any additional supplements, which were able, instead, to stimulate growth and lactate production by P. pentosaceus.

Screening, purification and characterization of thermostable, protease resistant Bacteriocin active against methicillin resistant Staphylococcus aureus (MRSA)

BACKGROUND

The emergence of serious issues of multidrug resistance in the past few years have enforced the use of bacteriocins for combating infections. Threat posed to public health by various multidrug resistant (MDR) organisms can be resolved by discovering new antimicrobial proteins with broad spectrum of inhibition.

RESULTS

In the current study, Bacteriocin (BAC-IB17) produced by Bacillus subtilis KIBGE-IB17 is found to be effective against different strains of methicillin resistant Staphylococcus aureus (MRSA). The approximate molecular mass of BAC-IB17 is 10.7 kDa. This unique bacteriocin is found to be highly thermostable and pH stable in nature. It also showed its stability against various heavy metals, organic solvents, surfactants and proteolytic enzymes. Amino acid profile of BAC-IB17 clearly showed that this protein mainly consists of non-polar and basic amino acids whereas; some acidic amino acids were also detected. Sequence of first 15 amino acid residues obtained from N-terminal sequencing of BAC-IB17 were NKPEALVDYTGVXNS.

CONCLUSIONS

The anti-MRSA property of purified bacteriocin may be used to prevent the spread of MRSA infections. Remarkable features of BAC-IB17 suggests its applications in various pharmaceutical and food industries as it can function under a variety of harsh environmental conditions.

Stability of Bacteriocin-Like Inhibitory Substance (BLIS) Produced by Pediococcus acidilactici kp10 at Different Extreme Conditions

Nowadays, bacteriocin industry has substantially grown replacing the role of chemical preservatives in enhancing shelf-life and safety of food. The progress in bacteriocin study has been supported by the emerging of consumer demand on the applications of natural food preservatives. Since food is a complex ecosystem, the characteristics of bacteriocin determine the effectiveness of their incorporation into the food products. Among four commercial media (M17 broth, MRS broth, tryptic soy broth, and nutrient broth) tested, the highest growth of Pediococcus acidilactici kp10 and bacteriocin-like-inhibitory substance (BLIS) production were obtained in the cultivation with M17. BLIS production was found to be a growth associated process where the production was increased concomitantly with the growth of producing strain, P. acidilactici kp10. The antimicrobial property of BLIS against three indicator microorganisms (Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus) remained stable upon heating at 100°C but not detectable at 121°C. The BLIS activity was also observed to be stable and active at a wide pH range (pH 2 to pH 7). The BLIS activity remained constant at -20°C and -80°C for 1 month of storage. However, the activity dropped after 3 and 6 months of storage at 4°C, -20°C, and -80°C with more than 80% reduction. The ability of bacteriocin from P. acidilactici kp10 to inhibit food-borne pathogens while remaining stable and active at extreme pH and temperature is of potential interest for future applications in food preservatives.

Empirical comparison of web-based antimicrobial peptide prediction tools

Motivation

Antimicrobial peptides (AMPs) are innate immune molecules that exhibit activities against a range of microbes, including bacteria, fungi, viruses and protozoa. Recent increases in microbial resistance against current drugs has led to a concomitant increase in the need for novel antimicrobial agents. Over the last decade, a number of AMP prediction tools have been designed and made freely available online. These AMP prediction tools show potential to discriminate AMPs from non-AMPs, but the relative quality of the predictions produced by the various tools is difficult to quantify.

Results

We compiled two sets of AMP and non-AMP peptides, separated into three categories-antimicrobial, antibacterial and bacteriocins. Using these benchmark data sets, we carried out a systematic evaluation of ten publicly available AMP prediction methods. Among the six general AMP prediction tools-ADAM, CAMPR3(RF), CAMPR3(SVM), MLAMP, DBAASP and MLAMP-we find that CAMPR3(RF) provides a statistically significant improvement in performance, as measured by the area under the receiver operating characteristic (ROC) curve, relative to the other five methods. Surprisingly, for antibacterial prediction, the original AntiBP method significantly outperforms its successor, AntiBP2 based on one benchmark dataset. The two bacteriocin prediction tools, BAGEL3 and BACTIBASE, both provide very good performance and BAGEL3 outperforms its predecessor, BACTIBASE, on the larger of the two benchmarks.

Contact

gaberemu@ngha.med.sa or william-noble@uw.edu.

Supplementary information

Supplementary data are available at Bioinformatics online.

Membrane-acting bacteriocin purified from a soil isolate Pediococcus pentosaceus LB44 shows broad host-range

Bacteriocin LB44 was purified from cell-free supernatant (CFS) of Pediococcus pentosaceus LB44 using activity-guided chromatography techniques. It was stable up to 121 °C, pH 2.0-6.0, sensitive to proteinase K, papain and trypsin, and retained complete activity in the presence of organic solvents tested. The molecular weight of bacteriocin was ∼6 kDa and initial ten amino acid residues (GECGMCXECG) suggested a new compound. The loss in viable cell count and K⁺ ion efflux of target cells of Micrococcus luteus suggested bactericidal activity. The cell membrane of bacteriocin-treated cells was found to be ruptured which was further confirmed by Fourier Transform Infrared (FTIR) analysis suggesting interaction of bacteriocin with phospholipids in cell membrane. It showed broad host-range and inhibited the growth of Lactobacillus delbrueckii NRRL B-4525, L. plantarum NRRL B-4496, L. acidophilus NRRL B-4495, Enterococcus hirae LD3, Weissella confusa LM85, Staphylococcus aureus, Salmonella typhi ATCC 13311, Serratia marcescens ATCC 27137, Pseudomonas aeruginosa ATCC 27853, Proteus vulgaris ATCC 29905, Haloferax larsenii HA1, HA3, HA8, HA9 and HA10. These properties suggested a new bacteriocin from soil isolate P. pentosaceus LB44 which may offers possible applications in food-safety and therapeutics.

Purification and characterization of two new cell-bound bioactive compounds produced by wild Lactococcus lactis strain

Novel compounds and innovative methods are required considering that antibiotic resistance has reached a crisis point. In the study, two cell-bound antimicrobial compounds produced by Lactococcus lactis ID1.5 were isolated and partially characterized. Following purification by cationic exchange and a solid-phase C18 column, antimicrobial activity was recovered after three runs of RPC using 60% (v/v) and 100% (v/v) of 2-propanol for elution, suggesting that more than one antimicrobial compound were produced by L. lactis ID1.5, which were in this study called compounds AI and AII. The mass spectrum of AI and AII showed major intensity ions at m/z 1070.05 and 955.9 Da, respectively. The compound AI showed a spectrum of antimicrobial activity mainly against L. lactis species, while the organisms most sensitive to compound AII were Bacillus subtilis, Listeria innocua, Streptococcus pneumoniae and Pseudomonas aeruginosa. The antimicrobial activity of both compounds was suppressed by treatment with Tween 80. Nevertheless, both compounds showed high stability to heat and proteases treatments. The isolated compounds, AI and AII, showed distinct properties from other antimicrobial substances already reported as produced by L. lactis, and have a significant inhibitory effect against two clinically important respiratory pathogens.

Antifungal and Zearalenone Inhibitory Activity of Pediococcus pentosaceus Isolated from Dairy Products on Fusarium graminearum

The present study was aimed to evaluate the bio-control efficacy of Pediococcus pentosaceus isolated from traditional fermented dairy products originated from India, against the growth and zearalenone (ZEA) production of Fusarium graminearum. The cell-free supernatants of P. pentosaceus (PPCS) were prepared and chemical profiling was carried out by GC-MS and MALDI-TOF analysis. Chemical profiling of PPCS evidenced that, the presence of phenolic antioxidants, which are responsible for the antifungal activity. Another hand, MALDI-TOF analysis also indicated the presence of antimicrobial peptides. To know the antioxidant potential of PPCS, DPPH free radical scavenging assay was carried out and IC50 value was determined as 32 ± 1.89 μL/mL. The antifungal activity of P. pentosaceus was determined by dual culture overlay technique and zone of inhibition was recorded as 47 ± 2.81%, and antifungal activity of PPCS on F. graminearum was determined by micro-well dilution and scanning electron microscopic techniques. The minimum inhibitory concentration (MIC) of PPCS was determined as 66 ± 2.18 μL/mL in the present study. Also a clear variation in the micromorphology of mycelia treated with MIC value of PPCS compared to untreated control was documented. Further, the mechanism of growth inhibition was revealed by ergosterol analysis and determination of reactive oxygen species (ROS) in PPCS treated samples. The effects of PPCS on mycelial biomass and ZEA production were observed in a dose-dependent manner. The mechanism behind the suppression of ZEA production was studied by reverse transcriptase qPCR analysis of ZEA metabolic pathway genes (PKS4 and PKS13), and results showed that there is a dose dependent down-regulation of target gene expression in PPCS treated samples. The results of the present study were collectively proved that, the antifungal and ZEA inhibitory activity of PPCS against F. graminearum and it may find a potential application in agriculture and food industry as a natural bio-controlling agent.

A Defensin from the Model Beetle Tribolium castaneum Acts Synergistically with Telavancin and Daptomycin against Multidrug Resistant Staphylococcus aureus

The red flour beetle Tribolium castaneum is a common insect pest and has been established as a model beetle to study insect development and immunity. This study demonstrates that defensin 1 from T. castaneum displays in vitro and in vivo antimicrobial activity against drug resistant Staphylococcus aureus strains. The minimum inhibitory concentration (MIC) of defensin 1 against 11 reference and clinical staphylococcal isolates was between 16–64 μg/ml. The putative mode of action of the defensin peptide is disruption of the bacterial cell membrane. The antibacterial activity of defensin 1 was attenuated by salt concentrations of 1.56 mM and 25 mM for NaCl and CaCl₂ respectively. Treatment of defensin 1 with the reducing agent dithiothreitol (DTT) at concentrations 1.56 to 3.13 mM abolished the antimicrobial activity of the peptide. In the presence of subinhibitory concentrations of antibiotics that also target the bacterial cell envelope such as telavancin and daptomycin, the MIC of the peptide was as low as 1 μg/ml. Moreover, when tested against an S. aureus strain that was defective in D-alanylation of the cell wall, the MIC of the peptide was 0.5 μg/ml. Defensin 1 exhibited no toxicity against human erythrocytes even at 400 μg/ml. The in vivo activity of the peptide was validated in a Caenorhabditis elegans-MRSA liquid infection assay. These results suggest that defensin 1 behaves similarly to other cationic AMPs in its mode of action against S. aureus and that the activity of the peptide can be enhanced in combination with other antibiotics with similar modes of action or with compounds that have the ability to decrease D-alanylation of the bacterial cell wall.

Bacteriocinogenic potential of a probiotic strain Bacillus coagulans [BDU3] from Ngari

Bacteriocin producing strain BDU3 was isolated from a traditional fermented fish of Manipur Ngari. The strain BDU3 was identified as Bacillus coagulans by phenotypic and genotypic characterization. The BDU3 produced novel bacteriocin, which showed an antimicrobial spectrum toward a wide spectrum of food borne, and closely related pathogens with a MIC that ranged between 0.5 and 2.5 μg/mL. The isolate was able to tolerate pH as low as 2.0 and up to 0.2% bile salt concentration. Three step purification was employed to increase the specific activity of the antimicrobial compound. The fractions were further chromatographed by Rp-HPLC C-18 column and the purified bacteriocin had a specific activity of ∼8500 AU/mg. However, the potency of bacteriocin was susceptible to digestion with Proteinase K, Pepsin, SDS, EDTA and Urea. Molecular mass of purified bacteriocin was found to be 1.4 kDa using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). The functional group was revealed by FTIR analysis. The cytotoxicity assay (MTT) using purified bacteriocin showed 2 times lower EC50 values compared to SDS. This is the smaller bacteriocin ever reported before from B. coagulans with greater antimicrobial potency with lower cytotoxicity. This bacteriocin raises the possibilities to be used as a biopreservative in food industries.