Antimicrobial activity of bacteria from marine sponge Suberea mollis and bioactive metabolites of Vibrio sp. EA348

Discovery of potential bioactive metabolites from sponge-associated bacteria have gained attraction in recent years. The current study explores the potential of sponge (Suberea mollis) associated bacteria against bacterial and fungal pathogens. Sponge samples were collected from Red sea in Obhur region, Jeddah, Saudi Arabia. Of 29 isolated bacteria belong to four different classes i.e. Firmicutes (62%), γ-Proteobacteria (21%), α-Proteobacteria (10%) and Actinobacteria (7%). Among them nineteen (65%) bacterial strains showed antagonistic activity against oomycetes and only 3 (10%) bacterial strains were active against human pathogenic bacteria tested. Most bioactive genera include Bacillus (55%), Pseudovibrio (13%) and Ruegeria (10%). Enzyme production (protease, lipase, amylase, cellualse) was identified in 12 (41%) bacterial strains where potential strains belonging to γ-Proteobacteria and Firmicutes groups. Production of antimicrobial metabolites and hydrolysates in these bacteria suggest their potential role in sponge against pathogens. Further bioactive metabolites from selected strain of Vibrio sp. EA348 were identified using LC-MS and GC–MS analyses. We identified many active metabolites including antibiotics such as Amifloxacin and fosfomycin. Plant growth hormones including Indoleacetic acid and Gibberellin A3 and volatile organic compound such as methyl jasmonate were also detected in this strain. Our results highlighted the importance of marine bacteria inhabiting sponges as potential source of antimicrobial compounds and plant growth hormones of pharmaceutical and agricultural significance.     

Biofilm Formation and Detachment in Gram-Negative Pathogens Is Modulated by Select Bile Acids

Biofilms are a ubiquitous feature of microbial community structure in both natural and host environments; they enhance transmission and infectivity of pathogens and provide protection from human defense mechanisms and antibiotics. However, few natural products are known that impact biofilm formation or persistence for either environmental or pathogenic bacteria. Using the combination of a novel natural products library from the fish microbiome and an image-based screen for biofilm inhibition, we describe the identification of taurine-conjugated bile acids as inhibitors of biofilm formation against both Vibrio cholerae and Pseudomonas aeruginosa. Taurocholic acid (1) was isolated from the fermentation broth of the fish microbiome-derived strain of Rhodococcus erythropolis and identified using standard NMR and MS methods. Screening of the twelve predominant human steroidal bile acid components revealed that a subset of these compounds can inhibit biofilm formation, induce detachment of preformed biofilms under static conditions, and that these compounds display distinct structure-activity relationships against V. cholerae and P. aeruginosa. Our findings highlight the significance of distinct bile acid components in the regulation of biofilm formation and dispersion in two different clinically relevant bacterial pathogens, and suggest that the bile acids, which are endogenous mammalian metabolites used to solubilize dietary fats, may also play a role in maintaining host health against bacterial infection.     

The plant-derived chalcone Xanthoangelol targets the membrane of Gram-positive bacteria

Xanthoangelol is a geranylated chalcone isolated from fruits of Amorpha fructicosa that exhibits antibacterial effects at low micromolar concentration against Gram-positive bacterial pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecium and Enterococcus faecalis. We demonstrate that Xanthoangelol treatment of Gram-positive bacteria affects bacterial membrane integrity and leads to a leakage of intracellular metabolites. This correlates with a rapid collapse of the membrane potential and results in a fast and strong bactericidal effect. Proteomic profiling of Xanthoangelol-treated cells revealed signatures of cell wall and/or membrane damage and oxidative stress. Xanthoangelol specifically disturbs the membrane of Gram-positive bacteria potentially by forming pores resulting in cell lysis. In contrast, Xanthoangelol treatment of human cells showed only mildly hemolytic and cytotoxic effects at higher concentrations. Therefore, geranylated chalcones such as Xanthoangelol are promising lead structures for new antimicrobials against drug-resistant gram-positive pathogens.     

Acid-Sensitive Enteric Pathogens Are Protected from Killing under Extremely Acidic Conditions of pH 2.5 when They Are Inoculated onto Certain Solid Food Sources

Gastric acidity is recognized as the first line of defense against food-borne pathogens, and the ability of pathogens to resist this pH corresponds to their oral infective dose (ID). Naturally occurring and genetically engineered acid-sensitive enteric pathogens were examined for their ability to survive under acidic conditions of pH 2.5 for 2 h at 37°C when inoculated onto ground beef. Each of the strains displayed significantly high survival rates under these normally lethal conditions. The acid-sensitive pathogens Campylobacter jejuni and Vibrio cholerae, which were protected at lower levels from acid-induced killing by ground beef under these conditions, were sensitive to killing in acidified media at pH 5.0 but survived at pH 6.0. Salmonella inoculated onto the surface of preacidified ground beef could not survive if the pH on the surface of the beef was 2.61 or lower but was viable if the surface pH was 3.27. This implies that the pH of the microenvironment occupied by the bacteria on the surface of the food source is critical for their survival. Salmonella was also shown to be protected from killing when inoculated onto boiled egg white, a food source high in protein and low in fat. These results may explain why Salmonella species have a higher oral ID of approximately 10⁵ cells when administered under defined conditions but have been observed to cause disease at doses as low as 50 to 100 organisms when consumed as part of a contaminated food source. They may also help explain why some pathogens are associated primarily with food-borne modes of transmission rather than fecal-oral transmission.     

Assessing the diversity of bacterial communities from marine sponges and their bioactive compounds

Symbiotic bacteria play vital roles in the survival and health of marine sponges. Sponges harbor rich, diverse and species-specific microbial communities. Symbiotic marine bacteria have increasingly been reported as promising source of bioactive compounds. A culturomics-based study was undertaken to study the diversity of bacteria from marine sponges and their antimicrobial potential. We have collected three sponge samples i.e. Acanthaster carteri, Rhytisma fulvum (soft coral) and Haliclona caerulea from north region (Obhur) of Red Sea, Jeddah Saudi Arabia. Total of 144 bacterial strains were isolated from three marine sponges using culture dependent method. Screening of isolated strains showed only 37 (26%) isolates as antagonists against oomycetes pathogens (P. ultimum and P. capsici). Among 37 antagonistic bacteria, only 19 bacterial strains exhibited antibacterial activity against human pathogens (Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 8739, Enterococcus faecalis ATCC 29212). Four major classes of bacteria i.e γ-Proteobacteria, α-Proteobacteria, Firmicutes and Actinobacteria were recorded from three marine sponges where γ-Proteobacteria was dominant class. One potential bacterial strain Halomonas sp. EA423 was selected for identification of bioactive metabolites using GC and LC-MS analyses. Bioactive compounds Sulfamerazine, Metronidazole-OH and Ibuprofen are detected from culture extract of strain Halomonas sp. EA423. Overall, this study gives insight into composition and diversity of antagonistic bacterial community of marine sponges and coral from Red Sea and presence of active metabolites from potential strain. Our results showed that these diverse and potential bacterial communities further need to be studied to exploit their biotechnological significance.     

Benzylideneacetone and other phenylethylamide bacterial metabolites induce apoptosis to kill insects

Xenorhabdus and Photorhabdus are entomopathogenic bacteria that can induce immunosuppression against target insects by suppressing eicosanoid biosynthesis, leading to fatal septicemia. These bacteria can synthesize and release secondary metabolites such as benzylideneacetone (BZA) and other phenylethylamide compounds that can inhibit phospholipase A₂ (PLA₂) and shut down eicosanoid biosynthesis. However, insecticidal activities of these bacterial metabolites remain unclear. Thus, the objective of this study was to assess cytotoxicities of BZA and seven other bacterial metabolites to insect cells. These eight bacterial metabolites exhibited significant cytotoxicities against an insect cell line Sf9 at micromolar range. Especially, BZA and cPY were highly potent at low micromolar range. When these eight bacterial metabolites were injected to hemocoels of Spodoptera exigua larvae, they significantly decreased total count of hemocytes. In Sf9 cell line and hemocytes, these bacterial metabolites induced cell membrane blebbings, apoptotic vesicles, and genomic DNA fragmentation. Terminal deoxyribonucleotidyl transferase nick end translation assay showed that these bacterial metabolites caused significant DNA breakages in cells in a dose-dependent manner. However, a pan caspase inhibitor treatment significantly rescued the cell death induced by these bacterial metabolites. Cytotoxicities of these bacterial metabolites were highly correlated with their insecticidal activities. These results indicate that the insecticidal activities of the bacterial metabolites may be induced by their apoptotic activities against hemocytes and other insect cells. Taken together, these results suggest that phenylethylamide compounds might have potential as novel insecticides.     

Antimicrobial activity of some plant extracts against bacterial strains causing food poisoning diseases

Prevention of food spoilage and food poisoning pathogens is usually achieved by use of chemical preservatives which have negative impacts including: human health hazards of the chemical applications, chemical residues in food & feed chains and acquisition of microbial resistance to the used chemicals. Because of such concerns, the necessity to find a potentially effective, healthy safer and natural alternative preservatives is increased. Within these texts, Plant extracts have been used to control food poisoning diseases and preserve foodstuff. Antimicrobial activity of five plant extracts were investigated against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi using agar disc diffusion technique. Ethanolic extracts of Punica granatum, Syzygium aromaticum, Zingiber officinales and Thymus vulgaris were potentially effective with variable efficiency against the tested bacterial strains at concentration of 10 mg/ml while extract of Cuminum cyminum was only effective against S. aureus respectively. P. granatum and S. aromaticum ethanolic extracts were the most effective plant extracts and showed bacteriostatic and bactericidal activities against the highly susceptible strains of food borne pathogenic bacteria (S. aureus and P. aeruginosa) with MIC's ranged from 2.5 to 5.0 mg/ml and MBC of 5.0 and 10 mg/ml except P. aeruginosa which was less sensitive and its MBC reached to 12.5 mg/ml of S. aromaticum respectively. These plant extracts which proved to be potentially effective can be used as natural alternative preventives to control food poisoning diseases and preserve food stuff avoiding healthy hazards of chemically antimicrobial agent applications.     

Application of bacteriophages in post-harvest control of human pathogenic and food spoiling bacteria

Bacteriophages have attracted great attention for application in food biopreservation. Lytic bacteriophages specific for human pathogenic bacteria can be isolated from natural sources such as animal feces or industrial wastes where the target bacteria inhabit. Lytic bacteriophages have been tested in different food systems for inactivation of main food-borne pathogens including Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Salmonella enterica, Shigella spp., Campylobacter jejuni and Cronobacter sakazkii, and also for control of spoilage bacteria. Application of lytic bacteriophages could selectively control host populations of concern without interfering with the remaining food microbiota. Bacteriophages could also be applied for inactivation of bacteria attached to food contact surfaces or grown as biofilms. Bacteriophages may receive a generally recognized as safe status based on their lack of toxicity and other detrimental effects to human health. Phage preparations specific for L. monocytogenes, E. coli O157:H7 and S. enterica serotypes have been commercialized and approved for application in foods or as part of surface decontamination protocols. Phage endolysins have a broader host specificity compared to lytic bacteriophages. Cloned endolysins could be used as natural preservatives, singly or in combination with other antimicrobials such as bacteriocins.     

Antioxidant and antimicrobial activities of Spirulina platensis extracts and biogenic selenium nanoparticles against selected pathogenic bacteria and fungi

This study investigated the antimicrobial and antioxidant activity of three Spirulina extracts (methanol, acetone, and hexane) and the biological selenium nanoparticles (SeNPs) fabricated by Bacillus subtilis AL43. The results showed that Spirulina extracts exhibited antimicrobial activity against tested pathogens. Besides, Spirulina extracts significantly scavenged ABTS and DPPH radicals in a dose-dependent manner. The methanolic extract had higher total phenolic content, antimicrobial activity, and antioxidant activity than other extracts. The selenium nanoparticles were synthesized by Bacillus subtilis AL43 under aerobic conditions and were characterized as spherical, crystalline with a size of 65.23 nm and a net negative charge of ?22.7. We evidenced that SeNPs possess considerable antimicrobial activity against three gram-positive, three gram-negative bacteria, and three strains from both Candida sp. and Aspergillus sp. Moreover, SeNPs were able to scavenge ABTS and DPPH radicals in a dose-dependent manner. An association was found between the total phenolic content of Spirulina and SeNPs and their biological activities. Our results indicate that Spirulina and SeNPs with significant antimicrobial and antioxidant activities seem to be successful candidates for safe and reliable medical applications.     

Impact of Violacein-Producing Bacteria on Survival and Feeding of Bacterivorous Nanoflagellates

We studied the role of bacterial secondary metabolites in the context of grazing protection against protozoans. A model system was used to examine the impact of violacein-producing bacteria on feeding rates, growth, and survival of three common bacterivorous nanoflagellates. Freshwater isolates of Janthinobacterium lividum and Chromobacterium violaceum produced the purple pigment violacein and exhibited acute toxicity to the nanoflagellates tested. High-resolution video microscopy revealed that these bacteria were ingested by the flagellates at high rates. The uptake of less than three bacteria resulted in rapid flagellate cell death after about 20 min and cell lysis within 1 to 2 h. In selectivity experiments with nontoxic Pseudomonas putida MM1, flagellates did not discriminate against pigmented strains. Purified violacein from cell extracts of C. violaceum showed high toxicity to nanoflagellates. In addition, antiprotozoal activity was found to positively correlate with the violacein content of the bacterial strains. Pigment synthesis in C. violaceum is regulated by an N-acylhomoserine lactone (AHL)-dependent quorum-sensing system. An AHL-deficient, nonpigmented mutant provided high flagellate growth rates, while the addition of the natural C. violaceum AHL could restore toxicity. Moreover, it was shown that the presence of violacein-producing bacteria in an otherwise nontoxic bacterial diet considerably inhibited flagellate population growth. Our results suggest that violacein-producing bacteria possess a highly effective survival mechanism which may exemplify the potential of some bacterial secondary metabolites to undermine protozoan grazing pressure and population dynamics.     

Bactericidal effect of silver nanoparticles against multidrug-resistant bacteria

Infections caused by drug-resistant microorganisms result in significant increases in mortality, morbidity, and cost related to prolonged treatments. The antibacterial activity of silver nanoparticles against some drug-resistant bacteria has been established, but further investigation is needed to determine whether these particles could be an option for the treatment and prevention of drug-resistant microbial infections. Hence, we challenged different drug-resistant pathogens of clinical importance (multidrug-resistant Pseudomonas aeruginosa, ampicillin-resistant Escherichia coli O157:H7 and erythromycin-resistant Streptococcus pyogenes) with a suspension of silver nanoparticles. By means of a luciferase-based assay, it was determined that silver nanoparticles (1) inactivate a panel of drug-resistant and drug-susceptible bacteria (Gram positive and Gram negative), (2) exert their antibacterial activity through a bactericidal rather than bacteriostatic mechanism, and (3) inhibit the bacterial growth rate from the time of first contact between the bacteria and the nanoparticles. Additionally, strains with a resistant phenotype to silver nanoparticle were developed and used to explore the bactericidal mode of action of silver nanoparticles. Through a Kirby–Bauer test, it was shown that silver nanoparticles’ general mechanism of bactericidal action is based on inhibition of cell wall synthesis, protein synthesis mediated by the 30s ribosomal subunit, and nucleic acid synthesis. Our data suggest that silver nanoparticles are effective broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for use in pharmaceutical products and medical devices that may help to prevent the transmission of drug-resistant pathogens in different clinical environments.     

Comparative sequence analysis of bacterial symbionts from the marine sponges Geodia cydonium and Ircinia muscarum

Marine sponges (Porifera) live in a symbiotic relationship with microorganisms, primarily bacteria. Recently, several studies indicated that sponges are the most prolific source of biologically-active compounds produced by symbiotic microorganisms rather than by the sponges themselves. In the present study we characterized the bacterial symbionts from two Demospongiae, Ircinia muscarum and Geodia cydonium. We amplified 16S rRNA by PCR, using specific bacterial-primers. The phylogenetic analysis revealed the presence of nine bacterial clones from I. muscarum and ten from G. cydonium. In particular, I. muscarum resulted enriched in Bacillus species and G. cydonium in Proteobacterium species. Since these bacteria were able to produce secondary metabolites with potential biotechnological and biopharmaceutical applications, we hypothesized that I. muscarum and G. cydonium could be a considered as a “gold mine” of natural products.     

Isolation and identification of endophytic bacteria from root tissues of Salvia miltiorrhiza Bge. and determination of their bioactivities

Endophytic bacteria are microorganisms that live in host plants, but do not cause diseases to the hosts. This study examined the occurrence, distribution, growth-promoting and antifungal activities of endophytes in the root of Salvia miltiorrhiza Bge. Six endophytic bacterial strains, which belong to genera of Pseudomonas, Rhizobium, Bacillus and Novosphingobium, were isolated from the root of healthy S. miltiorrhiza. Cell suspension (approx. 10⁹ cell?·?ml^?1) of two isolates and cell-free fermentation filtrate of four isolates substantially promoted the growth of hypocotyl and radicle of muskmelon seeds. The cell-free fermentation filtrate of six isolates had no inhibiting effect on tested pathogenic fungi, namely Fusarium solani, F. oxysporum f. sp. vasinfectum and F. oxysporum. Six compounds were isolated from one of the six endophytic bacteria, namely, Bacillus aryabhattai, and two of these compounds displayed certain antifungal activity against three tested S. miltiorrhiza pathogens. Our work indicates that endophytic bacteria occur in the root of S. miltiorrhiza, and that associated bacterial isolates have growth-promoting effect on muskmelon seeds and are expected to be a potential source for bioactive metabolites.     

First report of secondary metabolites,Violaceol I and Violaceol II produced by endophytic fungus,Trichoderma polyalthiae and their antimicrobial activity

Bioactive compounds of endophytic fungus Trichoderma polyalthiae were extracted from culture broth media. The crude extracts showed strong antimicrobial activity against human pathogens. Biologically active compounds were isolated and purified by chromatographic methods. The structures of the pure compounds were elucidated by spectroscopic methods. They were identified as Violaceol I and Violaceol II. These compounds were detected as secondary metabolites produced by this genus for the first time. Violaceol I and II had a broad spectrum of antimicrobial activity against human pathogens, including Gram-positive bacteria (Staphylococcus saprophyticus, Staphylococcus aureus, Methicillin-Resistant S. aureus, Bacillus subtilis, Bacillus cereus) and Gram-negative bacteria (Salmonella typhimurium, Shigella sonnei) and Candida albicans. Violaceol I exhibited Minimal Inhibitory Concentration (MIC) values (<9.765–156.25 μg/mL) that were higher than Violaceol II (<9.765–312.5 μg/mL). Additionally, the MIC value of the phenol violaceol from this taxon was lower than the previous reports.     

Isolation and characterization of a co-producer of fengycins and surfactins, endophytic Bacillus amyloliquefaciens ES-2, from Scutellaria baicalensis Georgi

An endophytic bacterium was isolated from Chinese medicinal plant Scutellaria baicalensis Georgi. The phylogenetic and physiological characzterization indicated that the isolate, strain ES-2, was Bacillus amyloliquefaciens, which produced two families of secondary metabolites with broad-spectrum antibacterial and antifungal activities. Culture filtrate of ES-2 displayed antagonism against some phytopathogenic, food-borne pathogenic and spoilage bacteria and fungi owing to the existence of antimicrobial compounds. A HPLC-MS analysis showed two series of ion peaks from the culture filtrate. A further electrospray ionization/collision-induced dissociation spectrum revealed that the two series ion peaks represented different fengycin homologues and surfactin homologues, respectively, which had a potential for food preservation and the control of several fungal plant diseases.     

Secondary Metabolites of <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> CHA0 Drive Complex Non-Trophic Interactions with Bacterivorous Nematodes

Non-trophic interactions are increasingly recognised as a key parameter of predator–prey interactions. In soil, predation by bacterivorous nematodes is a major selective pressure shaping soil bacterial communities, and many bacteria have evolved defence mechanisms such as toxicity. In this study, we show that extracellular secondary metabolites produced by the model soil bacterium Pseudomonas fluorescens CHA0 function as a complex defence strategy against bacterivorous nematodes. Using a collection of functional mutants lacking genes for the biosynthesis of one or several extracellular metabolites, we evaluated the impact of bacterial secondary metabolites on the survival and chemotactic behaviour of the nematode Caenorhabditis elegans. Additionally, we followed up the stress status of the nematodes by measuring the activation of the abnormal DAuer Formation (DAF) stress cascade. All studied secondary metabolites contributed to the toxicity of the bacteria, with hydrogen cyanide efficiently repelling the nematodes, and both hydrogen cyanide and 2,4-DAPG functioning as nematicides. Moreover, these metabolites elicited the DAF stress response cascade of C. elegans, showing that they affect nematode physiology already at sublethal concentrations. The results suggest that bacterial secondary metabolites responsible for the suppression of plant pathogens strongly inhibit bacterivorous nematodes and thus likely contribute to the resistance of bacteria against predators in soil.     

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.     

Enhanced virulence of Beauveria bassiana against Thrips tabaci by the addition of bacterial metabolites derived from Xenorhabdus hominickii

Xenorhabdus and Photorhabdus are two bacterial genera specifically symbiotic to Steinernema and Heterorhabditis, which are the entomopathogenic nematode genera, respectively. These bacteria are well known to produce potent secondary metabolites suppressing insect immune responses. This study aimed to develop a potent microbial insecticide against the onion thrips, Thrips tabaci, using the bacterial metabolites. Among the chemical insecticides that have been used to control the thrips, spinosad was highly effective against both larvae and adults of T. tabaci. Three different entomopathogenic fungi were also effective to kill the thrips. However, the fungal virulence was much less than the control efficacy of the chemical insecticide, spinosad. To enhance the fungal virulence of Beauveria bassiana (Bb), the bacterial culture broth of Xenorhabdus/Photorhabdus was added to suppress the thrips immune defense. Among six different bacterial species, X. hominickii (Xh) produced highly potent metabolites to enhance the fungal virulence. Indeed, four different bacterial metabolites (GameXPeptide, benzylideneacetone, oxindole, and 3-ethoxy-4-methoxyphenol) of the bacteria suppressed the gene expressions of an antimicrobial peptide, lysozyme, which was highly inducible to the fungal infection. To optimize the mixture ratio of fungal and bacterial pathogens, the fungal conidia and bacterial culture broth were freeze-dried and mixed in different ratios. Laboratory and field assays showed that a mixture spray of freeze-dried Xh culture broth (3 g) and Bb conidia (1.17 × 10⁹ conidia) in a liter was effective to control T. tabaci infesting welsh onion.     

Efficacies of Nisin A and Nisin V Semipurified Preparations Alone and in Combination with Plant Essential Oils for Controlling Listeria monocytogenes

The food-borne pathogenic bacterium Listeria is known for relatively low morbidity and high mortality rates, reaching up to 25 to 30%. Listeria is a hardy organism, and its control in foods represents a significant challenge. Many naturally occurring compounds, including the bacteriocin nisin and a number of plant essential oils, have been widely studied and are reported to be effective as antimicrobial agents against spoilage and pathogenic microorganisms. The aim of this study was to investigate the ability of semipurified preparations (SPP) containing either nisin A or an enhanced bioengineered derivative, nisin V, alone and in combination with low concentrations of the essential oils thymol, carvacrol, and trans-cinnamaldehyde, to control Listeria monocytogenes in both laboratory media and model food systems. Combinations of nisin V-containing SPP (25 μg/ml) with thymol (0.02%), carvacrol (0.02%), or cinnamaldehyde (0.02%) produced a significantly longer lag phase than any of the essential oil-nisin A combinations. In addition, the log reduction in cell counts achieved by the nisin V-carvacrol or nisin V-cinnamaldehyde combinations was twice that of the equivalent nisin A-essential oil treatment. Significantly, this enhanced activity was validated in model food systems against L. monocytogenes strains of food origin. We conclude that the fermentate form of nisin V in combination with carvacrol and cinnamaldehyde offers significant advantages as a novel, natural, and effective means to enhance food safety by inhibiting food-borne pathogens such as L. monocytogenes.