Enterococcus faecium isolated from honey synthesized bacteriocin-like substances active against different Listeria monocytogenes strains

Selective breeding of cold-tolerant black soldier fly (Hermetia illucens) larvae: Gut microbial shifts and transcriptional patterns

The larvae of black soldier fly (BSFL) convert organic waste into insect proteins used as feedstuff for livestock and aquaculture. BSFL production performance is considerably reduced during winter season. Herein, the intraspecific diversity of ten commercial BSF colonies collected in China was evaluated. The Bioforte colony was subjected to selective breeding at 12 °C and 16 °C to develop cold-tolerant BSF with improved production performance. After breeding for nine generations, the weight of larvae, survival rate, and the dry matter conversion rate significantly increased. Subsequently, intestinal microbiota in the cold-tolerant strain showed that bacteria belonging to Morganella, Dysgonomonas, Salmonella, Pseudochrobactrum, and Klebsiella genera were highly represented in the 12 °C bred, while those of Acinetobacter, Pseudochrobactrum, Enterococcus, Comamonas, and Leucobacter genera were significantly represented in the 16 °C bred group. Metagenomic revealed that several animal probiotics of the Enterococcus and Vagococcus genera were greatly enriched in the gut of larvae bred at 16 °C. Moreover, bacterial metabolic pathways including carbohydrate, lipid, amino acids, and cofactors and vitamins, were significantly increased, while organismal systems and human diseases was decreased in the 16 °C bred group. Transcriptomic analysis revealed that the upregulated differentially expressed genes in the 16 °C bred groups mainly participated in Autophagy-animal, AMPK signaling pathway, mTOR signaling pathway, Wnt signaling pathway, FoxO signaling pathway, Hippo signaling pathway at day 34 under 16 °C conditions, suggesting their significant role in the survival of BSFL. Taken together, these results shed lights on the role of intestinal microflora and gene pathways in the adaptation of BSF larvae to cold stress.

Antibacterial Sesquiterpene Lactones from Kaunia lasiophthalma

Phytochemical study of the species Kaunia lasiophthalma enabled the isolation of three undescribed and three known guaianolide-type sesquiterpene lactones, and one new benzofuran. The bioguided fractionation methodology was successful in detecting antimicrobial metabolites against Staphylococcus aureus strains and permitted the description of undescribed guaianolide-type sesquiterpene lactones with substitution patterns matching all those described in the Oxylobinae subtribe.

Anti-bacterial, anti-biofilm and anti-quorum sensing activities of honey: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Man has used honey to treat diseases since ancient times, perhaps even before the history of medicine itself. Several civilizations have utilized natural honey as a functional and therapeutic food to ward off infections. Recently, researchers worldwide have been focusing on the antibacterial effects of natural honey against antibiotic-resistant bacteria.

AIM OF THE STUDY

This review aims to summarize research on the use of honey properties and constituents with their anti-bacterial, anti-biofilm, and anti-quorum sensing mechanisms of action. Further, honey's bacterial products, including probiotic organisms and antibacterial agents which are produced to curb the growth of other competitor microorganisms is addressed.

MATERIALS AND METHODS

In this review, we have provided a comprehensive overview of the antibacterial, anti-biofilm, and anti-quorum sensing activities of honey and their mechanisms of action. Furthermore, the review addressed the effects of antibacterial agents of honey from bacterial origin. Relevant information on the antibacterial activity of honey was obtained from scientific online databases such as Web of Science, Google Scholar, ScienceDirect, and PubMed.

RESULTS

Honey's antibacterial, anti-biofilm, and anti-quorum sensing activities are mostly attributed to four key components: hydrogen peroxide, methylglyoxal, bee defensin-1, and phenolic compounds. The performance of bacteria can be altered by honey components, which impact their cell cycle and cell morphology. To the best of our knowledge, this is the first review that specifically summarizes every phenolic compound identified in honey along with their potential antibacterial mechanisms of action. Furthermore, certain strains of beneficial lactic acid bacteria such as Bifidobacterium, Fructobacillus, and Lactobacillaceae, as well as Bacillus species can survive and even grow in honey, making it a potential delivery system for these agents.

CONCLUSION

Honey could be regarded as one of the best complementary and alternative medicines. The data presented in this review will enhance our knowledge of some of honey's therapeutic properties as well as its antibacterial activities.

Antimicrobial Properties, Functional Characterisation and Application of Fructobacillus fructosus and Lactiplantibacillus plantarum Isolated from Artisanal Honey

Honey is a valuable reservoir of lactic acid bacteria (LAB) and, particularly, of fructophilic LAB (FLAB), a relatively novel subgroup of LAB whose functional potential for human and food application has yet to be explored. In this study, FLAB and LAB strains have been isolated from honeys of different floral origins and selected for their broad antimicrobial activity against typical foodborne pathogenic bacteria and spoilage filamentous fungi. The best candidates, two strains belonging to the species Lactiplantibacillus plantarum and Fructobacillus fructosus, were submitted to partial characterisation of their cell free supernatants (CFS) in order to identify the secreted metabolites with antimicrobial activity. Besides, these strains were examined to assess some major functional features, including in vitro tolerance to the oro-gastrointestinal conditions, potential cytotoxicity against HT-29 cells, adhesion to human enterocyte-like cells and capability to stimulate macrophages. Moreover, when the tested strains were applied on table grapes artificially contaminated with pathogenic bacteria or filamentous fungi, they showed a good ability to antagonise the growth of undesired microbes, as well as to survive on the fruit surface at a concentration that is recommended to develop a probiotic effect. In conclusion, both LAB and FLAB honey-isolated strains characterised in this work exhibit functional properties that validate their potential use as biocontrol agents and for the design of novel functional foods. We reported antimicrobial activity, cytotoxic evaluation, probiotic properties and direct food application of a F. fructosus strain, improving the knowledge of this species, in particular, and on FLAB, more generally.

Physicochemical Characteristics and Bioactive Compounds of Different Types of Honey and Their Biological and Therapeutic Properties: A Comprehensive Review

Honey is considered to be a functional food with health-promoting properties. However, its potential health benefits can be affected by individual composition that varies between honey types. Although studies describing the health benefits of Tualang honey (TH), Kelulut honey (KH), and Sidr honey (SH) are scarce, these honey types showed a comparable therapeutic efficacy to Manuka honey (MH). The purpose of this review is to characterise the physicochemical, biological, and therapeutic properties of TH, KH, and SH. Findings showed that these honeys have antibacterial, antifungal, antiviral, antioxidant, antidiabetic, antiobesity, anticancer, anti-inflammatory and wound-healing properties and effects on the cardiovascular system, nervous system, and respiratory system. The physicochemical characteristics of TH, KH, and SH were compared with MH and discussed, and results showed that they have high-quality contents and excellent biological activity sources. Flavonoids and polyphenols, which act as antioxidants, are two main bioactive molecules present in honey. The activity of honey depends on the type of bee, sources of nectar, and the geographic region where the bees are established. In conclusion, TH, KH, and SH could be considered as natural therapeutic agents for various medicinal purposes compared with MH. Therefore, TH, KH, and SH have a great potential to be developed for modern medicinal use.

Response of sensitive and resistant Listeria monocytogenes strains against bacteriocins produced by different Enterococcus spp. strains

Listeria monocytogenes is a relevant foodborne pathogen causing invasive listeriosis in humans, a disease with high mortality rates. Its ubiquity and growth characteristics enable this pathogen to survive harsh food processing environments. The addition of bacteriocins, antimicrobial peptides ribosomally synthesized by certain bacteria, appears as a natural alternative to control this pathogen in food. However, the emergence of L. monocytogenes strains resistant to the inhibitory action of bacteriocins has been detected. In order to analyse the development of this resistance, different properties of L. monocytogenes strains susceptible to bacteriocins (strains 01/155, 99/287 and 99/267) and their respective resistant isolates (strains 01/155B6R, 99/287B6R, 99/286C1R, 99/287 Mo1R, 99/287 M1bR, 99/287 M2dR, 99/267B6R), were compared in this work. Differences were analysed in: a) growth of the pathogen strains in direct contact with bacteriocin solution, in co-cultures with the producing strain, or with different sugars; b) response to antibiotics typically used against listeriosis; c) changes in cell morphology, observed by transmission or scanning electron microscopy; d) expression of mobility and haemolysin activity, two of L. monocytogenes main virulence factors; and e) biofilm formation ability. For all the isolates, the acquired resistance was permanent and crossed between the different bacteriocins under study. An inhibitory effect was observed for resistant strains only when they were grown in mixed culture with any of the bacteriocin-producing strains, with an acidified medium as additional growth stress. In all cases, the decrease in viability was lower for resistant strains and followed a particular profile for each strain. The variation of sugar substrate influenced resistant variants growth ability, with a more pronounced difference in the medium supplemented with glucose. Susceptibility to antibiotics was similar or higher for resistant variants, while neither the mobility nor the haemolytic activity presented differences among resistant or susceptible strains. Finally, the resistant variants showed a greater capacity to form biofilms, although this effect was reversed when grown in the presence of bacteriocins. Each resistant isolate had a particular behaviour pattern, and the acquisition of resistance appeared to be strain and bacteriocin dependent. These results contribute to the knowledge of L. monocytogenes bacteriocin-resistance development, which is essential to favour the use of these peptides as biopreservatives.

Bacteriocin activity of various iranian honey-associated bacteria and development of a simple medium for enhanced bacteriocin activity

PURPOSE

Honey is a promising source of bacterial strains producing metabolites with antimicrobial activity. There is a great variety in the antimicrobial activity of honey from different areas of nature. Therefore, the aim of present study was to investigate the antibacterial activity of Iranian honey from different regions and to optimize the culture condition for the highly potent bacterial isolate.

METHODS

Honey samples were collected from ten different regions of Iran and were screened for bacteriocin-producing bacteria. The best bacteriocin-producing strain was characterized and identified by 16S rDNA analysis. One-factor-at-a-time method was used for optimization of culture medium and the yield and time-course of bacteriocin production were compared in both shake flask and bio-reactor.

RESULTS

The Bacillus subtilis SB1 that was isolated from Sabalan honey showed potent antibacterial activity with prominent thermal stability. The optimum medium for the bacteiocin production was a yeast extract-based medium. The optimum incubation temperature for bacteriocin production was 34 °C. Bacteriocin production was higher near neutral pH conditions than that produced at acidic or alkaline environment. The results of cell growth and bacteriocin assays revealed that the exponential phase of growth and antibacterial compounds production was started rapidly in bioreactor than flask.

CONCLUSIONS

Findings of this study supported the folkloric application of honey against some infectious diseases. B.subtilis SB1 that isolated from Sabalan honey was a potential source for bacteriocins-like compounds. Our studies suggested a simple buffered nitrogen-based medium for SB1 growth and bacteriocin activity in both shake flask and bioreactor.

Anti-Proliferative and Anti-Biofilm Potentials of Bacteriocins Produced by Non-Pathogenic Enterococcus sp

The incidence of cancer is increasing worldwide; likewise, the emergence of antibiotic-resistant biofilm-forming pathogens has led to a tremendous increase in morbidity and mortality. This study aimed to evaluate the probiotic properties of bacteriocin-producing Enterococcus sp. with a focus on their anti-biofilm and anticancer activities. Three of 79 Enterococcus isolates (FM43, FM65, FM50) were identified as producers of broad-spectrum bioactive molecules and were molecularly characterized as Enterococcus faecium by 16S rRNA sequencing. Phenotypic and genotypic screening for potential virulence factors revealed no factors known to promote pathogenicity. Treatment with proteinase K resulted in diminished antimicrobial activity; PCR-based screening for bacteriocin genes suggested the presence of both entA and entB genes that encode enterocins A and B, respectively. Maximum antimicrobial activity was detected during the early stationary phase, while activity disappeared after 24 h in culture. Bacteriocins from these isolates were stable at high temperatures and over a wide range of pH. Interestingly, crude supernatants of Ent. faecium FM43 and Ent. faecium FM50 resulted in significant destruction (80% and 48%, respectively; P < 0.05) of Streptococcus mutans ATCC 25175-associated preformed biofilms. Moreover, in vitro cytotoxicity assays revealed that extracts from Ent. faecium isolates FM43, FM65, and FM50 inhibited Caco-2 cell proliferation by 76.9%, 70%, and 85.3%, respectively. Taken together, the multifunctional capabilities of the microbial-derived proteins identified in our study suggest potentially important roles as alternative treatments for biofilm-associated infections and cancer.

Current status and application of lactic acid bacteria in animal production systems with a focus on bacteria from honey bee colonies

Lactic acid bacteria (LAB) are widely distributed in nature and, due to their beneficial effects on the host, are used as probiotics. This review describes the applications of LAB in animal production systems such as beekeeping, poultry, swine and bovine production, particularly as probiotics used to improve health, enhance growth and reproductive performance. Given the importance of honeybees in nature and the beekeeping industry as a producer of healthy food worldwide, the focus of this review is on the coexistence of LAB with honeybees, their food and environment. The main LAB species isolated from the beehive and their potential technological use are described. Evidence is provided that 43 LAB bacteria species have been isolated from beehives, of which 20 showed inhibition against 28 species of human and animal pathogens, some of which are resistant to antibiotics. Additionally, the presence of LAB in the beehive and their relationship with antibacterial properties of honey and pollen is discussed. Finally, we describe the use of lactic bacteria from bee colonies and their antimicrobial effect against foodborne pathogens and human health. This review broadens knowledge by highlighting the importance of honeybee colonies as suppliers of LAB and functional food.

The Antimicrobial Potential of Bacteria Isolated from Honey Samples Produced in the Apiaries Located in Pomeranian Voivodeship in Northern Poland

The principal objective of this study was to determine whether the honeys produced in apiaries located in Pomeranian Voivodeship (Northern Poland) contain bacteria producing metabolites with growth inhibition potential against important human and animal pathogens. The pathogens included Staphylococcus aurues, Staphyloccocus epidermidis, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, and Candida albicans. From 12 samples of honey, 163 strains of bacteria were isolated. Activity against reference staphylococci: S. aurues ATCC 25923; S. aureus ATCC 29213; S. epidermidis 12228 was observed in 33 (20.3%), 38 (23.3%), and 41 (25.1%) isolates, respectively. High inhibitory activity was also found against Listeria monocytogenes ATCC 7644 in 34 strains (20.9%). Activity against Candida albicans ATCC 10231 and especially Gram-negative bacteria: Pseudomonas aeruginosa ATCC 27857 and Escherichia coli ATCC 25922 was rarely observed. Production of metabolites exhibiting activity against the three pathogens mentioned above was confirmed for 13 (7.8%), 3 (1.8%), and 2 (1.2%) isolates, respectively. Forty-six isolates were selected for further analysis. Within this group, metabolites synthesized by 18 producing strains (39.13%) inhibited growth of only one of the reference strains of pathogenic microorganisms. However, 14 (30.44%), 8 (17.39%), and 6 (13.04%) strains produced agents active against three, two, and four pathogens, respectively. Sequencing of the 16S rRNA gene revealed that 80.4% of these 46 producing strains belong to the genus Bacillus. However, some producing strains belonging to the genus of Peanibacillus, Lysinibacillus, Microbacterium, and Staphylococcus were also identified. Furthermore, the analysis of the sequences of 16S rRNA, as well as RAPD-PCR, exhibited a significant diversity in the strains tested, even in the case of bacteria isolated from the same honey (and classified to the same genus, usually Bacillus spp.). This observation suggests environmental origin (nectar, water, or pollen) of the producing strains. The research carried out confirmed that honey produced in Northern Poland is a promising source of strains of bacteria producing metabolites with antimicrobial activity.

Gram-Positive Bacteria with Probiotic Potential for the Apis mellifera L. Honey Bee: The Experience in the Northwest of Argentina

Apis mellifera L. is one of the most important natural pollinators of significant crops and flowers around the world. It can be affected by different types of illnesses: american foulbrood, nosemosis, varroasis, viruses, among others. Such infections mainly cause a reduction in honey production and in extreme situations, the death of the colony. Argentina is the world's second largest honey exporter and the third largest honey producer, after China and Turkey. Given both the prominence of the honey bee in nature and the economic importance of apiculture in Argentina and the world, it is crucial to develop efficient and sustainable strategies to control honey bee diseases and to improve bee colony health. Gram-positive bacteria, such as lactic acid bacteria, mainly Lactobacillus, and Bacillus spp. are promising options. In the Northwest of Argentina, several Lactobacillus and Bacillus strains from the honey bee gut and honey were isolated by our research group and characterized by using in vitro tests. Two strains were selected because of their potential probiotic properties: Lactobacillus johnsonii CRL1647 and Bacillus subtilis subsp. subtilis Mori2. Under independent trials with both experimental and commercial hives, it was determined that each strain was able to elicit probiotic effects on bee colonies reared in the northwestern region of Argentina. One result was the increase in egg-laying by the queen which therefore produced an increase in bee number and, consequently, a higher honey yield. Moreover, the beneficial bacteria reduced the incidence of two important bee diseases: nosemosis and varroosis. These results are promising and extend the horizon of probiotic bacteria to the insect world, serving beekeepers worldwide as a natural tool that they can administer as is, or combine with other disease-controlling methods.

Inhibition of Bacillus cereus Strains by Antimicrobial Metabolites from Lactobacillus johnsonii CRL1647 and Enterococcus faecium SM21

Bacillus cereus is an endospore-forming, Gram-positive bacterium able to cause foodborne diseases. Lactic acid bacteria (LAB) are known for their ability to synthesize organic acids and bacteriocins, but the potential of these compounds against B. cereus has been scarcely documented in food models. The present study has examined the effect of the metabolites produced by Lactobacillus johnsonii CRL1647 and Enterococcus faecium SM21 on the viability of select B. cereus strains. Furthermore, the effect of E. faecium SM21 metabolites against B. cereus strains has also been investigated on a rice food model. L. johnsonii CRL1647 produced 128 mmol/L of lactic acid, 38 mmol/L of acetic acid and 0.3 mmol/L of phenyl-lactic acid. These organic acids reduced the number of vegetative cells and spores of the B. cereus strains tested. However, the antagonistic effect disappeared at pH 6.5. On the other hand, E. faecium SM21 produced only lactic and acetic acid (24.5 and 12.2 mmol/L, respectively) and was able to inhibit both vegetative cells and spores of the B. cereus strains, at a final fermentation pH of 5.0 and at pH 6.5. This would indicate the action of other metabolites, different from organic acids, present in the cell-free supernatant. On cooked rice grains, the E. faecium SM21 bacteriocin(s) were tested against two B. cereus strains. Both of them were significantly affected within the first 4 h of contact; whereas B. cereus BAC1 cells recovered after 24 h, the effect on B. cereus 1 remained up to the end of the assay. The LAB studied may thus be considered to define future strategies for biological control of B. cereus.

Lactobacillus kunkeei YB38 from honeybee products enhances IgA production in healthy adults

AIMS

To identify lactic acid bacterial isolates, which promote immunoglobulin A (IgA) production in honeybee products and honeybees (Apis mellifera).

METHODS AND RESULTS

Pyrosequencing analysis of the microbiota of honeybee products and honeybees revealed the predominance of Lactobacillus kunkeei in honey, bee pollen, bee bread and royal jelly. Lactobacillus kunkeei was isolated from bee pollen, bee bread and honey stomach, and its effect on IgA production was evaluated in vitro. Heat-killed YB38 and YB83 isolates from bee pollen promoted IgA production in mouse Peyer's Patch cells and had little mitogenic activity or effect on IL-2 production in mouse spleen cells in comparison with Listeria monocytogenes, which does exhibit mitogen activity. A pilot study in 11 healthy adults showed that 4-week intake of 1000 mg day(-1) heat-killed YB38 increased secretory IgA (SIgA) concentrations and secretion in saliva with no adverse effects.

CONCLUSION

Heat-killed Lact. kunkeei YB38 from bee pollen increases IgA production and may safely improve immune responsiveness.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of microbiota analysis of royal jelly and the immune efficacy of Lact. kunkeei from honeybee products in humans.

Selection of potential probiotic Enterococcus faecium isolated from Portuguese fermented food

Four Enterococcus faecium strains isolated from fermented products were evaluated for potential use as probiotic strains. In addition to efaAfm gene, commonly found in E. faecium food isolates, none of the isolates possessed virulence genes and none had positive reactions for the production of tyramine, histamine, putrescine and cadaverine in the screening medium used. All of these four isolates proved to be resistant to 65 °C. E. faecium 119 did not show antimicrobial activity against any of the target bacteria investigated. E. faecium 85 and 101 inhibited Listeria innocua and E. faecium DSMZ 13590. The strain E. faecium 120 inhibited seven target bacteria (Listeria monocytogenes 7946, L. monocytogenes 7947, L. innocua 2030c, L. innocua NCTC 11286, E. faecium DSMZ 13590, Enterococcus faecalis ATCC 29212 and Staphylococcus aureus ATCC 29213) and was chosen as the representative to assess the ability to survive gastrointestinal tract passage simulation, as well as the protective role of two food matrices (skim milk and Alheira) during its passage. For both matrices used, no significant differences (p<0.05) were obtained between the types of digestion - quick and slow passage simulation. In the skim milk matrix the isolate was reduced to values below the detection limit of the enumeration technique by the end of the two digestions, in contrast to the Alheira matrix, for which isolate 120 showed a reduction of only ca. 1 log CFU/ml. The E. faecium strain 120 was shown to be a potential candidate for further investigations as a potential probiotic culture.

Effect of Complex Food Environment on Production of Enteriocin IN 3531 with Enterococcus faecium IN3531 as a Starter in Chinese Fermentation Paocai Making

Enterococcus faeciumIN3531 has beensuccessfully confirmed to have no disease-causing factors and antibioticresistance and it had been confirmed that the ability to produce bacteiocins inMRS. In this study, the effects of the complex food environment in Chinese fermentationpaocai making on Enteriocin IN3531 production were studied. It was concludedthat the complex food environment didn’t thoroughly interferes with bacteriocinproduction levels. Results obtained showed that the suitable fermentationconditions for enterocin IN3531 production in Chinese fermentation paocai makingusingEnterococcus faeciumIN3531 asa starter were the initial salt concentration of 2%, the inoculum size of 3%,the fermentation temperature of 35 °C, the ratio of material to liquid of 30%, fermentationtime of 108 hours.

Reduction of tyramine by addition of Schizandra chinensis baillon in Cheonggukjang

This study was performed to examine the microorganisms responsible for the high tyramine content of Cheonggukjang, a traditional Korean fermented soy food, and to establish a technology for controlling the growth of these microorganisms. The tyramine content in 13 collected Cheonggukjang samples averaged 604.9 mg/kg. Since the tyramine content measured from most samples was sufficient to cause harm to the human body, it is necessary to control its production in food. Enterococci were confirmed to be the bacterial species producing most of the tyramine through the microbial examination and were present in high numbers from not detected (<10(1)) to 7.0 × 10(10) colony-forming units (CFU)/g. To control the growth of enterococci, various plant extracts with antimicrobial activity, common salts, and variable temperature conditions were tested. It was found that 4 samples among the 159 plant extracts had a strong antimicrobial activity in Cheonggukjang, especially against Enterococcus faecium, showing viable cell counts of <10(1)-10(3) CFU/g after 24 h of ripening, which were significantly lower values compared to the control (10(9)-10(11) CFU/g). The Cheonggukjang with the addition of the four plant extracts showed ∼83%-95% lower concentrations of tyramine compared to the control. Cheonggukjang prepared with the Schizandra chinensis Baillon extract had the lowest tyramine content without sacrificing the sensory quality. Not only was the bacterial species of E. faecium reduced more remarkably, by up to 10(3) CFU/g compared to the 10(9)-10(11) CFU/g shown in the control, but it also decreased the tyramine content by up to 91%.

Antibacterial activity of naringin derivatives against pathogenic strains

AIMS

To study the antimicrobial activity of naringin (NAR), a flavonoid extracted from citrus industry waste, and NAR derivatives [naringenin (NGE), prunin and alkyl prunin esters] against pathogenic bacteria such as L. monocytogenes, E. coli O157:H7 and S. aureus. The relationship between the structure of the chemical compounds and their antagonistic effect was also analysed.

METHODS AND RESULTS

The agar dilution technique and direct contact assaying were applied. NGE, prunin and NAR showed no antimicrobial activity at a concentration of 0.25 mmol l(-1). Similarly, fatty acids with a chain length between C2 and C18 showed no antimicrobial activity at the same concentration. However, prunin-6″-O-acyl esters presented high antibacterial activity, mainly against Gram-positive strains. This activity increased with increasing chain length (up to 10-12 carbon atoms). Alkyl prunin esters with 10-12 carbon atoms diminished viability of L. monocytogenes by about 3 log orders and S. aureus by 6 log orders after 2 h of contact at 37°C and at a concentration of 0.25 mmol l(-1). The compounds examined were not effective against any of the Gram-negative strains assayed, even at the highest concentration.

CONCLUSIONS

Addition of sugars to the aglycone did not enhance its antimicrobial activity. Attachment of a saturated aliphatic chain with 10-12 carbon atoms to the A ring of the flavonoid (or to sugars attached to this ring), seems to be the most promising modification. In conclusion, alkyl prunin esters with a chain length of C10-C12 have promising features as antimicrobial agents because of their high antilisterial and antistaphylococcal activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that it is possible to obtain NAR derivatives with important antimicrobial activity, especially against Gram-positive pathogenic bacteria. It also provides guidelines on the structural modifications in similar molecules to enhance the antimicrobial activity.

Antimicrobial properties of prunin, a citric flavanone glucoside, and its prunin 6″-O-lauroyl ester

AIMS

To determine the antimicrobial potential of prunin (P), a flavanone glucoside resulting from the hydrolysis of naringin present in grapefruit, and of its prunin 6″-O-lauroyl ester (PL), synthesized by enzymatic catalysis.

METHODS AND RESULTS

P and its lauroyl ester were tested against Gram-negative and Gram-positive bacteria, yeasts and moulds. P showed no inhibitory effect against the micro-organisms assayed, but stimulated growth of Pseudomonas aeruginosa and different Bacilllus sp. However, 150 μg ml(-1) of PL inhibited Escherichia coli, Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, many Bacillus sp., Staphylococcus aureus ATCC29213, Enterococcus avium DSMZ17511, and different Listeria monocytogenes strains. In the last case, L. monocytogenes, sensitive or bacteriocin-resistant cells, lost nearly 4-log reductions after 30 min of contact. A bactericidal mode of action was determined using both scanning and transmission electronic microscopies.

CONCLUSIONS

PL could be used as a food additive, because at low concentration (150 μg ml(-1)) it exhibited antimicrobial activity against important food-borne pathogens. A bactericidal effect was also determined on L. monocytogenes sensitive and bacteriocin-resistant mutant strains. P did not show any antimicrobial property at all.

SIGNIFICANCE AND IMPACT OF THE STUDY

PL is a potential antimicrobial compound with a high anti-Listeria property.