In silico design of polycationic antimicrobial peptides active against <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

Antimicrobial peptides (AMPs) have the potential to become valuable antimicrobial drugs in the coming years, since they offer wide spectrum of action, rapid bactericidal activity, and low probability for resistance development in comparison with traditional antibiotics. The search and improvement of methodologies for discovering new AMPs to treat resistant bacteria such as Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa are needed for further development of antimicrobial products. In this work, the software Peptide ID 1.0^® was used to find new antimicrobial peptide candidates encrypted in proteins, considering the physicochemical parameters characteristics of AMPs such as positive net charge, hydrophobicity, and sequence length, among others. From the selected protein fragments, new AMPs were designed after conservative and semi-conservative modifications and amidation of the C-terminal region. In vitro studies of the antimicrobial activity of the newly designed peptides showed that two peptides, P3-B and P3-C, were active against P. aeruginosa Escherichia coli and A. baumannii with low minimum inhibitory concentrations. Peptide P3-C was also active against K. pneumoniae and S. aureus. Furthermore, bactericidal activity and information on the possible mechanisms of action are described according to the scanning electron microscopy studies.     

First Record of Larval Secretions of <Emphasis Type="Italic">Cochliomyia macellaria</Emphasis> (Fabricius, 1775) (Diptera: Calliphoridae) Inhibiting the Growth of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Maggot debridement therapy (MDT) consists on the intentional and controlled application of sterilized larvae of the order Diptera on necrotic skin lesions with the purpose of cleaning necrotic tissue and removing pathogenic bacteria. During MDT, a marked antimicrobial activity has been reported in literature specially associated with antibacterial substances from Lucilia sericata (Meigen); however, regarding Cochliomyia macellaria (Fabricius), little is known. This study aimed to evaluate in vitro inhibition of bacterial growth of Pseudomonas aeruginosa and Staphylococcus aureus in contact with excretions and secretions (ES) from C. macellaria larvae. Larval ES were extracted in sterile distilled water and divided in three groups: ES, containing 400 μL of autoclaved ES; ES+BAC, containing 400 μL of autoclaved ES+0.5-μL bacterial inoculum; and CONT-BAC, containing 400 μL of sterile distilled water +0.5 μL of bacterial inoculum. Aliquots of each experimental group were plated by spreading onto Petri dishes. Seedings were made at 0, 1, 2, 4, and 12 h after the extraction of ES. In ES+BAC groups, inhibition of S. aureus was verified between times 1 and 2 h and P. aeruginosa was inhibited between 0 and 4 h. There was no growth observed in any ES group. In the CONT-BAC groups, the number of colonies from time 4 h became countless for S. aureus and decreased for P. aeruginosa. As reported in the literature, we note here that ES have excellent bactericidal activity for both gram-positive and gram-negative bacteria, and this study shows for the first time the action of the bactericidal activity of exosecretions of C. macellaria against S. aureus and P. aeruginosa.     

The Phenolic Contents and Antimicrobial Activities of Some Marine Algae from the Mediterranean Sea (Algeria)

In this study, three marine algae collected from western coast of algerian mediteranean sea (Ulva lactuca, Dictyota dichotoma, and Corallina elongata) were tested using the agar-well diffusion method for their production of antibacterial and antifungal agents on various organisms that cause diseases of humans and plants (Eschirichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Salmonella sp, Candida albicans, and Penicillium sp.). The total phenol content and antimicrobial activity were determined using different crude seaweeds extracts (methanol, diethylether, and chloroform). The results show that the chloroform extracts of (Ulva lactuca and Corallina elongata) had the highest activity against E. coli and Salmonella sp. The methanol extract obtained from (Ulva lactuca, Dictyota dichotoma, and Corallina elongata) showed antifungal activity for Candida albicans. The results of the study revealed that the seaweeds from Algeria appear to have immense potential as a source of antibacterial and antifungal compounds; they can be used in treating diseases caused by these organisms.     

Comparison of Antimicrobial Properties of Silver Nanoparticles Synthesized from Selected Bacteria

Green silver nanoparticle (AgNP) biosynthesis is facilitated by the enzyme mediated reduction of Ag ions by plants, fungi and bacteria. The antimicrobial activity of green AgNPs is useful to overcome the challenge of antimicrobial resistance. Antimicrobial properties of biosynthesized AgNPs depend on multiple factors including culture conditions and the microbial source. The antimicrobial activity of AgNPs biosynthesized by Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and Acinetobacter baumannii (confirmed clinical isolate) were investigated in this study. Biosynthesis conditions (AgNO₃ concentration, pH, incubation temperature and incubation time) were optimized to obtain the maximum AgNP yield. Presence of AgNPs was confirmed by observing a characteristic UV–Visible absorbance peak in 420–435 nm range. AgNP biosynthesis was optimal at 0.4 g/L AgNO₃ concentration under alkaline conditions at 60–70 °C. The biosynthesized AgNPs showed higher stability compared to chemogenized AgNPs in the presence of electrolytes. AgNPs synthesized by P. aeruginosa were the most stable while NPs of S. aureus were the least stable. AgNPs synthesized by P. aeruginosa and S. aureus showed good antimicrobial potential against E. coli, P. aeruginosa, S. aureus, MRSA and Candida albicans. AgNPs synthesized by S. aureus had greater antimicrobial activity. The antimicrobial activity of NPs may vary depending on the size and the morphology of NPs.     

Bioprospecting of <Emphasis Type="Italic">Diaporthe terebinthifolii</Emphasis> LGMF907 for antimicrobial compounds

Antibiotic-resistant bacteria have been observed with increasing frequency over the past decades, driving the search for new drugs and stimulating the interest in natural products sources. Endophytic fungi from medicinal plants represent a great source of novel bioactive compounds useful to pharmaceutical and agronomical purposes. Diaporthe terebinthifolii is an endophytic species isolated from Schinus terebinthifolius, a plant used in popular medicine for several health problems. The strain D. terebinthifolii LGMF907 was previously reported by our group to produce secondary metabolites with biological activity against phytopathogens. Based on these data, strain LGMF907 was chosen for bioprospecting against microorganisms of clinical importance and for characterization of major secondary metabolites. In this study, different culture conditions were evaluated and the biological activity of this strain was expanded. The crude extracts demonstrated high antibacterial activity against Escherichia coli, Micrococcus luteus, Saccharomyces cerevisiae, methicillin-sensitive Staphylococcus aureus, and methicillin-resistant S. aureus. The compounds diaporthin and orthosporin were characterized and also showed activity against the clinical microorganisms evaluated. This study discloses the first isolation of diaporthin and orthosporin from D. terebinthifolii, and revealed the potential of this endophytic fungus to produce secondary metabolites with antimicrobial activity.     

Calcium-dependent antibacterial activity of donkey’s milk against <Emphasis Type="Italic">Salmonella</Emphasis>

The aim of this study was to examine the antibacterial activity of raw donkey’s milk (DM) against Salmonella Enteritidis and Salmonella Typhimurium as well as to determine the dependence of this antibacterial activity on calcium, lysozyme and lactoferrin content. Antibacterial assays were conducted in DM artificially contaminated with these Salmonella serotypes and then incubated at 38 °C for 8 hours. Calcium concentration was found to have a strong influence on the antibacterial activity of the contaminated DM samples supplemented with CaCl₂ and EDTA. The antibacterial activity of DM against the tested Salmonella strains was observed to be strongly calcium dependent, with the addition of CaCl₂ to DM samples improving its antibacterial potential against both pathogens. Salmonella Enteritidis appeared to be less sensitive to the antimicrobial agents in DM than S. Typhimurium. One explanation is the calcium-dependant antibacterial activity of DM is attributable to the calcium-binding ability of its lysozyme. Lysozyme may be the main antibacterial agent, most probably via a nonenzymatic mode of action against tested Salmonella strains.     

Synthesis of functionalized benzo[<Emphasis Type="Italic">f</Emphasis>]2<Emphasis Type="Italic">H</Emphasis>-chromenes and evaluation of their antimicrobial activities

Knoevenagel cyclocondensations of α-hydroxy naphthaldehyde with β-oxodithioesters and ketene dithioacetals yielded 2H-benzo[f]chromene-2-thiones and 2H-benzo[f]chromen-2-ones, respectively, in high yields. The newly synthesized compounds were evaluated for antifungal and antibacterial activities. Among them, compounds (2-furyl)(3-thioxo-3H-benzo[f]chromen-2-yl)methanone and phenyl(3-oxo-3H-benzo[f]chromen-2-yl)methanone exhibited excellent antifungal activity against tested fungi Curvularia lunata and Fusarium moniliforme. The highest antibacterial activity against the tested bacteria Escherichia coli and Staphylococcus aureus was observed for (4-chlorophenyl)(3-oxo-3H-benzo[f]chromen-2-yl)methanone. The results of antimicrobial screening demonstrate that (2-furyl)(3-thioxo-3H-benzo[f]chromen-2-yl)methanone, phenyl(3-oxo-3H-benzo[f]chromen-2-yl)methanone, and (4-chlorophenyl)(3-oxo-3H-benzo[f]chromen-2-yl)methanone are promising as antimicrobial drugs.     

<Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> as a Probiotic Potential from Kouzeh Cheese (Traditional Iranian Cheese) and Its Antimicrobial Activity

The aim of this study is to isolate and identify Lactobacillus plantarum isolates from traditional cheese, Kouzeh, and evaluate their antimicrobial activity against some food pathogens. In total, 56 lactic acid bacteria were isolated by morphological and biochemical methods, 12 of which were identified as Lactobacillus plantarum by biochemical method and 11 were confirmed by molecular method. For analyzing the antimicrobial activity of these isolates properly, diffusion method was performed. The isolates were identified by 318 bp band dedicated for L. plantarum. The isolated L. plantarum represented an inhibitory activity against four of the pathogenic bacteria and showed different inhibition halos against each other. The larger halos were observed against Staphylococcus aureus and Staphylococcus epidermidis (15 ± 0.3 and 14.8 ± 0.7 mm, respectively). The inhibition halo of Escherichia coli was smaller than that of other pathogen and some L. plantarum did not show any inhibitory activity against E. coli, which were resistant to antimicrobial compounds produced by L. plantarum. The isolated L. plantarum isolates with the antimicrobial activity in this study had strong probiotic properties. These results indicated the nutritional value of Kouzeh cheese and usage of the isolated isolates as probiotic strains.     

Isolation Purification and Characterization of Antimicrobial Peptides from <Emphasis Type="Italic">Cuminum cyminum</Emphasis> L. Seeds

In this work, antimicrobial peptides from Cuminum cyminum L. seeds were isolated and purified for the first time by 50% ethanol extraction, C18 reverse phase column chromatography and ion exchange chromatography for separation different peptides fraction. Then isolated fractions were characterized by Gel electrophoresis (SDS-PAGE), high-pressure liquid chromatography and the peptides components and molecular weights were determined by liquid chromatography and mass spectrometry. The extracts were tested against some strains of bacteria (E. coli and Staphylococcus aureus) and one strain of fungi (Candida albicans) using well diffusion and broth dilution assays. The extracts from C. cyminum L. seeds demonstrated a high degree of activity (some antibacterial effect) against the bacteria strains and аntifungal activity against the Candida albicans. However, the study indicates that the crude peptide extracts from C. cyminum L. seeds have promising antimicrobial and antioxidant activities that can be harnessed as leads for potential bioactive compounds.     

Effect of salt stress on the antimicrobial activity of <Emphasis Type="Italic">Ruta chalepensis</Emphasis> essential oils

In the current investigation, the biological activities of essential oils obtained from organs of Ruta chalepensis plants grown under salt stress (0, 50 and 100 mM NaCl) were analyzed. Their chemical composition was often investigated by GC/FID and GC–MS and the antimicrobial activities towards eight bacteria (Salmonella All, Salmonella K, Escherichia coli 45AG, Escherichia coli 45AI, Staphylococcus aureus 9402, Staphylococcus aureus 02B145, Listeria 477 and Pseudomonas aeruginosa ATCC 10145) and five fungi strains (Aspergillus, Saccharomycee crvisiale, Streptomyces griseus, Fusarium solani and Penicillium thomii) were studied. Results revealed that salt increased essential oil production in leaves at 50 and 100 mM NaCl. A total of 20 compounds were identified in leaves, undecan-2-one, nonan-2-one and geijerene being the dominant ones. In stems, 21 compounds were found; they were dominated by decan-2-one, geijerene, nonan-2-one and undecan-2-one. In contrast, roots exhibited a large variation with 25 volatile compounds and octyl acetate, methyl decanoate, phytyl acetate were the major ones. Salt stress induced significant antibacterial activity changes, mainly in leaves and stems. In leaves, the minimum inhibitory and bactericidal concentration decreased at 100 mM NaCl against Listeria 477, the two strains of E. coli (45AG and 45AI) and P. aeruginosa but it increased versus other bacteria. In stems, salt increased oil antibacterial activity against all strains except P. aeruginosa ATCC 10145. Root oil showed the least antibacterial activity under saline conditions versus Listeria 477 and P. aeruginosa ATCC 10145. As regards antifungal activity, NaCl reduced the antifungal activity of essential oils against the majority of fungi strains.     

Synthesis,characterization and evaluation of antimicrobial and cytotoxic activities of biogenic silver nanoparticles synthesized from <Emphasis Type="Italic">Streptomyces xinghaiensis</Emphasis> OF1 strain

We report synthesis of silver nanoparticles (AgNPs) from Streptomyces xinghaiensis OF1 strain, which were characterised by UV–Vis and Fourier transform infrared spectroscopy, Zeta sizer, Nano tracking analyser, and Transmission electron microscopy. The antimicrobial activity of AgNPs alone, and in combination with antibiotics was evaluated against bacteria, namely Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis, and yeasts viz., Candida albicans and Malassezia furfur by using micro-dilution method. The minimum inhibitory concentration (MIC) and minimum biocidal concentration of AgNPs against bacterial and yeast strains were determined. Synergistic effect of AgNPs in combination with antibacterial and antifungal antibiotics was determined by FIC index. In addition, MTT assay was performed to study cytotoxicity of AgNPs alone and in combination with antibiotics against mouse fibroblasts and HeLa cell line. Biogenic AgNPs were stable, spherical, small, polydispersed and capped with organic compounds. The variable antimicrobial activity of AgNPs was observed against tested bacteria and yeasts. The lowest MIC (16 µg ml^?1) of AgNPs was found against P. aeruginosa, followed by C. albicans and M. furfur (both 32 µg ml^?1), B. subtilis and E. coli (both 64 µg ml^?1), and then S. aureus and Klebsiella pneumoniae (256 µg ml^?1). The high synergistic effect of antibiotics in combination with AgNPs against tested strains was found. The in vitro cytotoxicity of AgNPs against mouse fibroblasts and cancer HeLa cell lines revealed a dose dependent potential. The IC₅₀ value of AgNPs was found in concentrations of 4 and 3.8 µg ml^?1, respectively. Combination of AgNPs and antibiotics significantly decreased concentrations of both antimicrobials used and retained their high antibacterial and antifungal activity. The synthesis of AgNPs using S. xinghaiensis OF1 strain is an eco-friendly, cheap and nontoxic method. The antimicrobial activity of AgNPs could result from their small size. Remarkable synergistic effect of antibiotics and AgNPs offer their valuable potential in nanomedicine for clinical application as a combined therapy in the future.     

Isolation of <Emphasis Type="Italic">Lactobacillus</Emphasis> strains from shellfish for their potential use as probiotics

Microorganisms intended for use as probiotics in aquaculture should exert antimicrobial activity and be regarded as safe not only for their aquatic hosts but also for their surrounding environments and humans. The objective of this work was to investigate antimicrobial activity against various pathogens, bile salt tolerance, and acid tolerance of 65 presumptive Lactobacillus spp. isolated from shellfish samples. Four strains (HL1, HL12, HL20, and JL28) were selected after qualitatively identifying high levels of antimicrobial activity against bacteria including Staphylococcus aureus, Salmonella typhimurium, Salmonella enteritidis, Escherichia coli O157:H7, Vibrio ichthyoenteri, Edwardsiella tarda, Streptococcus iniae, and V. parahaemolyticus. The sequence analysis of their 16S rRNA genes revealed that the four strains belong to the Lactobacillus plantarum species. In addition, their survivability was tested in bile salt and acidic conditions to show their potential use as probiotics in the gastrointestinal tract.     

Study of the antibacterial activity of electro-activated solutions of salts of weak organic acids on <Emphasis Type="Italic">Salmonella enterica</Emphasis>, <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> and <Emphasis Type="Italic">Listeria monocytogenes</Emphasis>

This work assessed the antibacterial activity of electro-activated solutions of salts of weak organic acids (potassium acetate, potassium citrate and calcium lactate) on Salmonella enterica, Staphylococcus aureus and Listeria monocytogenes. This activity was compared in terms of minimal inhibitory (bactericidal) concentration to the effect of commercial acetic, citric and lactic acid at equivalent titratable acidity. Staining live/dead BacLight method was used to consider physiological state of bacteria following the evaluation of pathogenic strains during exposure to the tested solutions. The results demonstrated strong inhibitory activity of all electro-activated solutions. After 10 min of exposure to electro-activated potassium acetate, a reduction of ≥6 log CFU/ml of all bacteria was observed. The electro-activated potassium citrate demonstrated the lowest minimal inhibitory concentration. Nevertheless, its inactivation power was significantly higher than that of conjugated citric acid. Although electro-activated calcium lactate was found less effective in comparison with its conjugated acid form, after 10 min of contact with the tested pathogens, it induced a population reduction of 2.23, 2.97 and 5.57 log CFU/ml of S. aureus, L. monocytogenes and S. enterica, respectively.     

Use of a mixed culture strategy to isolate halophilic bacteria with antibacterial and cytotoxic activity from the Manaure solar saltern in Colombia

Background

Water evaporation in solar salterns creates salinity gradients that promote the adaptation of microbial species to different salinities. This competitive habitat challenges the metabolic capabilities of microorganisms and promotes alterations in their production of secondary metabolites. Thus, solar salterns are a potentially important source of new natural products. In Colombia, the most important and representative solar saltern is located in Manaure (La Guajira) in the north of Colombia. The aim of this study was to develop an alternative screening strategy to select halophilic bacteria as producers of bioactive compounds from mixed microbial cultures rather than individual environmental isolates. Brine and sediment samples from different ponds (across a salinity gradient) were inoculated in seven different culture media to grow bacteria and archaea, allowing for a total of 40 different mixed cultures. An organic extract from each mixed culture was obtained and tested against multidrug resistant pathogens, including Klebsiella pneumoniae, vancomycin-resistant Enterococcus faecium, methicillin-resistant Staphylococcus aureus and Bacillus subtilis. In addition, the extracts were tested against two human cancer cell lines, cervical adenocarcinoma (SiHa) and lung carcinoma (A-549).

Results

Twenty-four of the forty extracts from mixed cultures obtained from brine and sediment samples from the Manaure solar saltern showed antibacterial activity against Bacillus subtilis. Two extracts, referred to as A1SM3–29 and A1SM3–36, were also active against a methicillin-resistant Staphylococcus aureus, with the latter extract also showing slight cytotoxic activity against the assayed human lung cancer cell line. From this mixed culture, nine isolates were cultivated, and their extracts were tested against the same pathogens, resulting in the identification of a Vibrio sp. strain (A1SM3–36-8) with antimicrobial activity that was similar to that observed for the mixed culture extract. The extract of this strain was subjected to a bioautography assay, and 3 different fractions exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus. Based on the amount obtained for each fraction, F3 was selected to isolate and identify its metabolites. The major compound was identified by NMR and HRMS as 13-cis-docosenamide, an amide that has been previously reported to be an antimicrobial and cytotoxic compound.

Conclusions

Our results shows the utility of our strategy in detecting bioactive molecules in initial mixed cultures by biological assays, resulting in the isolation and characterization of Vibrio sp. A1SM3–36-8, a halophilic strain with great antibacterial and cytotoxic potential.

     

Antimicrobial Activity of Marine Bacterial Symbionts Retrieved from Shallow Water Hydrothermal Vents

Marine sponges and other sessile macro-organisms were collected at a shallow water hydrothermal site in Eyjafjörður, Iceland. Bacteria were isolated from the organisms using selective media for actinomycetes, and the isolates were screened for antimicrobial activity. A total of 111 isolates revealed antimicrobial activity displaying different antimicrobial patterns which indicates production of various compounds. Known test strains were grown in the presence of ethyl acetate extracts from one selected isolate, and a clear growth inhibition of Staphylococcus aureus was observed down to 0.1 % extract concentration in the medium. Identification of isolates shows different species of Actinobacteria with Streptomyces sp. playing the largest role, but also members of Bacilli, Alphaproteobacteria and Gammaproteobacteria. Sponges have an excellent record regarding production of bioactive compounds, often involving microbial symbionts. At the hydrothermal vents, however, the majority of active isolates originated from other invertebrates such as sea anemones or algae. The results indicate that antimicrobial assays involving isolates in full growth can detect activity not visible by other methods. The macro-organisms inhabiting the Eyjafjörður hydrothermal vent area host diverse microbial species in the phylum Actinobacteria with antimicrobial activity, and the compounds responsible for the activity will be subject to further research.     

Antimicrobial Effects of Peptides from Human Beta-Defensin-3 on Planktonic and Biofilm States of Streptococci

Human beta-defensin-3 (hBD3) acts as a first line of defense against both Gram-positive and Gram-negative bacteria infection. Streptococci are the significant cause for oral biofilm associated diseases. We synthesized three fragments (hBD3-1, hBD3-2, hBD3-3) from the hBD3 and evaluated the antibacterial efficacy on oral streptococci. All of the three fragments from hBD3 had good estimated solubility and hBD3-3 had a higher net positive charge than others. Structure analysis showed that the three fragments shared stable β-sheet structure, but tyrosine were not found in hBD3-2 and hBD3-3 by using Raman and circular dichroism spectroscopy. The inhibition ability of the peptides was examined on the bioactivity of Streptococcus oralis (S.oralis), Streptococcus sanguinis (S. sanguinis) and Streptococcus gordonii (S. gordonii) by minimal inhibitory concentration, minimum bactericidal concentration and anti-biofilm formation test. Three fragments had antimicrobial activity on planktonic state of streptococci, and S. oralis had much more sensitive to the three peptides. Results of antibiofilm experiment showed that streptococci biofilm formation was more sensitive to hBD3-3. Confocal laser scanning microscopy and scanning electron microscopy showed the decrease of biomass and bacterial morphology destruction, which indicated that the antimicrobial mechanism of hBD3-3 might involve an electrostatic charge-based impact on membrane permeability. In conclusion, hBD3-3 possessed the potential capacity for depressing the growth of bacteria, especially first colonizers during the development of oral biofilm. Powerful, endogenous antimicrobial peptide provides the potential to interfere with biofilm by disorganizing early biofilm formation and thereby inhibiting biofilm-associated diseases.     

Antibacterial compound produced by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> strain UICC B-40, an endophytic bacterium isolated from <Emphasis Type="Italic">Neesia altissima</Emphasis>

This study’s aim was to determine the identity of antibacterial compounds produced by Pseudomonas aeruginosa strain UICC B-40 and describe the antibacterial compounds’ mechanisms of action for damaging pathogenic bacteria cells. Isolation and identification of the compounds were carried out using thin layer chromatography (TLC), nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography mass spectrometry (LC-MS) analyses. Antibacterial activity was assayed via minimum inhibitory concentration (MIC) and the antibacterial compound mechanism was observed morphologically through scanning electron microscopy (SEM). This study successfully identified the (2E,5E)-phenyltetradeca-2,5-dienoate antibacterial compound (molecular weight 300 g/mol), composed of a phenolic ester, fatty acid and long chain of aliphatic group structures. MIC values for this compound were determined at 62.5 μg/ml against Staphylococcus aureus strain ATCC 25923. The mechanism of the compound involved breaking down the bacterial cell walls through the lysis process. The (2E,5E)-phenyltetradeca-2,5-dienoate compound exhibited inhibitory activity on the growth of Gram-positive bacteria.     

A New Broad-Spectrum Peptide Antibiotic Produced by <Emphasis Type="Italic">Bacillus brevis</Emphasis> Strain MH9 Isolated from Margalla Hills of Islamabad,Pakistan

The antimicrobial peptide from a bacterial strain is isolated from soil sample of Margalla Hills of Islamabad, Pakistan. The peptide is found to significantly inhibit the growth of both Gram-positive (Staphylococcus aureus ATCC 6538 and Micrococcus luteus ATCC 10240) and Gram-negative (Escherichia coli ATCC 25922 and Salmonella typhi ATCC 14028) bacteria as compared to gramicidin as standard. The bacterium is identified as Bacillus brevis strain MH9 based on phenotype and phylogenetic analysis. The antibacterial polypeptide was produced optimally at 35 °C after 48 h of growth, precipitated by 50 % ammonium sulphate, and further purified using HPLC. The sequential steps of purification decrease the peptide contents with prominent antibacterial activity. The peptide composed of 11 amino acid was further characterized by FT-IR and NMR. Results suggested that the peptide molecule is a novel antibacterial agent that is effective against both Gram-positive and Gram-negative bacteria. This study may have important implications for new peptide antibiotic that could be a new addition to treat infections.     

Purification and characteristics of a novel bacteriocin produced by <Emphasis Type="Italic">Enterococcus faecalis</Emphasis> L11 isolated from Chinese traditional fermented cucumber

Objective

To purify and characterize a novel bacteriocin with broad inhibitory spectrum produced by an isolate of Enterococcus faecalis from Chinese fermented cucumber.

Results

E. faecalis L11 produced a bacteriocin with antimicrobial activity against both Escherichia coli and Staphylococcus aureus. The amino acid sequence of the purified bacteriocin, enterocin L11, was assayed by Edman degradation method. It differs from other class II bacteriocins and exhibited a broad antimicrobial activity against not only Gram-positive bacteria, including Bacillus subtilis, S. aureus, Listeria monocytogenes, Sarcina flava, Lactobacillus acidophilus, L. plantarum, L. delbrueckii subsp. delbrueckii, L. delbrueckii subsp. bulgaricus and Streptococcus thermophilus, but also some Gram-negative bacteria including Salmonella typhimurium, E. coli and Shigella flexneri. Enterocin L11 retained 91 % of its activity after holding at 121 °C for 30 min. It was also resistant to acids and alkalis.

Conclusions

Enterocin L11 is a novel broad-spectrum Class II bacteriocin produced by E. faecalis L11, and may have potential as a food biopreservative.

     

Diversity and Probiotic Potential of Lactic Acid Bacteria Isolated from Horreh,a Traditional Iranian Fermented Food

The aim of this study was to evaluate the probiotic potential of lactic acid bacteria (LAB) strains isolated from Horreh. Some probiotic properties, e.g., resistance to acid, bile tolerance, antibacterial activity, and antibiotic susceptibility, were investigated. A total of 140 Gram-positive and catalase-negative isolates from Horreh were subjected to identification and grouping by cultural methods and the 16S rRNA sequencing. The new isolates were identified to be Lactobacillus (fermentum, plantarum, and brevis) Weissella cibaria, Enterococcus (faecium and faecalis), Leuconostoc (citreum and mesenteroides subsp. mesenteroides) and Pediococcus pentosaceus. Probiotic potential study of LAB isolates showed that Lb. plantarum and Leu. mesenteroides subsp. mesenteroides isolates were able to grow at pH 2.5 and 3.5. Lactobacillus plantarum (isolate A44) showed the highest cell hydrophobicity (84.5%). According to antibacterial activity tests, Listeria innocua and Staphylococcus aureus were the most sensitive indicators against the selected LAB strains, while Escherichia coli and Bacillus cereus were the most resistant. In addition, all the isolated LAB species were resistant to vancomycin. The results of the present study suggested that the Lactobacillus fermentum and plantarum isolated from Horreh, characterized in this study, have potential use for industrial purposes as probiotics.