Antibacterial Activity of Ethanolic Extract of Syzygium polyanthum L. (Salam) Leaves against Foodborne Pathogens and Application as Food Sanitizer

Compounds isolation from Syzygium cumini leaf extract against the Vibrio species in shrimp through bioassay-guided fractionation

This study was conducted to isolate and identify the bioactive compounds from the ethanolic extract of Syzygium cumini leaf against Vibrio species through a bioassay-guided fractionation. The ethanol extract was exposed to silica gel chromatography followed by reversed phase HPLC to isolate the most effective fraction against V. parahaemolyticus. Using further UHPLC-orbitrap-ion trap mass spectrometry, five compounds were isolated with broad-spectrum potency against a range of Vibrio species viz. V. parahaemolyticus, V. alginolyticus, V. harveyi, V. vulnificus and V. anguillarum. The IC50 values for the compounds ranged from 8 to 48 µg/mL against the most sensitive species V. vulnificus and 58 to >400 µg/mL against V. alginolyticus. The results of the toxicity tests demonstrated that the compounds were not harmful for shrimp. The study's findings indicate that S. cumini leaf extract may contain bioactive molecules that are able to be substituted for antibiotics to treat vibriosis in shrimp farming.

Phytochemical and antimicrobial properties of different plants and in silico investigation of their bioactive compounds in wound healing and rheumatism

In the current study the assessment of the antimicrobial and phytochemical properties of Cassia fistula, Musa paradisiaca, Ficus religiosa and Murraya koenigii plants extracts was carried out. The antibacterial potential of these plants extracts was tested against S. aureus and E. coli. The Cassia fistula and Ficus religiosa leaves showed the larger zone of inhibition in aqueous and butanolic extract respectively against Escherichia coli. Musa paradisiaca and Murraya koenigii leaves showed larger zone of inhibition in ethanolic extract against S. aureus. Qualitative phytochemical analysis showed the presence of alkaloids, flavonoids, phenols, terpenoids, steroids, glycosides, saponins, carbohydrates, proteins and tannins in all extracts while phylobatannins, emodins, anthocyanins and leucoanthocyanins were not present in these extracts. Quantitative phytochemical analysis showed the highest alkaloid content in the Murraya koenigii leaves. Highest tannin content and flavonoid content was found in Ficus religiosa leaves, while highest phenolic content was found in case of Cassia fistula. In addition to this antioxidant potential of all the extracts was determined. Musa paradisiaca leaves showed highest antioxidant potential as compared to other plant extracts. In silico analysis of bioactive components present in plant extracts was performed by molecular docking. The rutin and Glu from Musa paradisiaca and Murraya koenigii respectively, were docked with Glycogen Synthase Kinase 3 beta (1GSK-3beta) protein. Quercetin and rutin from Cassia fistula and Ficus religiosa respectively, were docked with C- reactive protein (CRP). The tested bioactive compounds showed good binding affinity with significant number of hydrogen bonds and can be used as a good alternative of synthetic drugs to treat rheumatism and wounds.

Rapeseed plant: biostimulation effects of plant growth-promoting Actinobacteria on metabolites and antioxidant defense system under elevated CO2 conditions

BACKGROUND

The present study set out to evaluate the potential of plant growth-promoting Actinobacteria (PGPB) in improving some physiological and molecular parameters of rapeseed (Brassica napus L.) plants under ambient and elevated CO2 conditions by assessing some nitrogen- and sulfur-containing metabolites, antioxidant defense system and antimicrobial activity. With this aim, a pot experiment was conducted where the rapeseed plants were treated with Actinobacterium sp. strain NCO2 (OQ451136) and were grown under two levels of air CO2 concentrations: ambient CO2 (aCO2 , 410 μmol CO2  mol-1 ); and elevated CO2 (eCO2 , 710 μmol CO2  mol-1 ).

RESULTS

There was an increase in the photosynthetic pigments (+35-80%) and photosynthesis rate (+20-34%) in PGPB-treated plants under eCO2 compared to control plants, resulting in further growth and biomass production (+53-294%). These results were associated with an enhancement in the content of total antioxidant capacity (+15-128%), polyphenols (+21-126%) and α-tocopherols (+20-138%) under both eCO2 and PGPB application (in combination or individual application), while only the combined treatment (eCO2  + PGPB) led to a significantly higher accumulation of antioxidant enzymes (+88-197%), β-tocopherols (+177%) and flavonoids (+155%). Moreover, nitrogen- and sulfur-containing metabolites (glucosinolates and amino acids) were improved by PGPB treatment and/or CO2 levels, in which PGPB increased the amino acid-derived glucosinolate induction by eCO2 with low levels of effective sulforaphane.

CONCLUSIONS

Therefore, the interaction effects of beneficial Actinobacteria and eCO2 are expected to boost the level of antioxidant molecules and to have a helpful role in improving plant biomass and adaptability to complicated climate changes in the future. © 2023 Society of Chemical Industry.

Antibacterial potential of silver nanoparticles (SP-AgNPs) synthesized from Syzygium polyanthum (Wight) Walp. against selected foodborne pathogens

Foodborne diseases continue to pose a significant global health concern, causing a considerable number of deaths worldwide. In response to concerns surrounding bacterial resistance and the limitations of traditional antibiotics, there is a growing interest in exploring natural antibacterial agents as potential alternatives for addressing foodborne pathogens. Nowadays efforts are being made on exploring the potential of natural antibacterial agents against foodborne pathogens. In this study, the antibacterial efficacy of silver nanoparticles synthesized using S. polyanthum leaves extract (SP-AgNPs) against selected Gram-negative and Gram-positive foodborne pathogens was investigated by using multiple assays, including the well diffusion assay (WDA), minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assay. The well diffusion assay demonstrated the inhibitory potential of SP-AgNPs against all tested foodborne pathogens, with inhibition zones ranging from 10.16 + 1.25 to 13.16 + 1.52 mm. Furthermore, the MIC values ranged from 0.008 to 0.125 mg/mL, indicating the potent antibacterial activity of SP-AgNPs across a broad spectrum of foodborne pathogens. The MBC values, ranging from 0.008 to 0.250 mg/mL, further confirming the bactericidal ability of SP-AgNPs against these pathogens. In the time-kill experiment, most foodborne pathogens were entirely killed after 4 h of incubation at 4 × MIC concentration. However, only E. coli, K. pneumoniae, and S. Typhimurium showed a reduction in population to 3 Log10 CFU/mL, indicating a strong bactericidal effect of SP-AgNPs on most tested pathogens. In conclusion, this study provides compelling evidence that SP-AgNPs exhibit potent antibacterial activity against selected foodborne pathogens. The findings suggest that SP-AgNPs synthesized using S. polyanthum leaves extract hold great promise as a novel antibacterial agent for effectively controlling foodborne pathogens. These findings contribute to continuing efforts in developing alternative strategies to prevent foodborne diseases and enhance food safety.

Bithionol Restores Sensitivity of Multidrug-Resistant Gram-Negative Bacteria to Colistin with Antimicrobial and Anti-biofilm Effects

Being among the few last-resort antibiotics, colistin (COL) has been used to treat severe infectious diseases, such as those caused by multidrug-resistant Gram-negative bacteria (MDR GNB). However, the appearance of colistin-resistant (COL-R) GNB has been frequently reported. Therefore, novel antimicrobial strategies need to be urgently sought to address this resistance challenge. In the present study, antimicrobial drug screening conducted revealed that bithionol (BT), approved by the Food and Drug Administration and used as an anthelminthic drug for paragonimiasis, exhibited a synergistic antibacterial effect with COL. Clinically isolated COL-R GNB were used as candidates to evaluate the synergistic antibacterial activity. The results revealed that BT could significantly reverse the sensitivity of COL-R GNB to COL. Furthermore, the combined application of BT and COL can reduce bacterial biofilm formation and have a scavenging effect on the mature biofilm in vitro. The damage caused to the bacterial cell membrane integrity by the BT/COL combination was observed under a fluorescence microscope. The fluorescence intensity of reactive oxygen species also increased in the experimental group. The BT/COL combination also exhibited a synergistic antibacterial effect in vivo. Importantly, BT was confirmed to be safe at the highest concentrations that exerted synergistic effects on all tested strains. In conclusion, our findings demonstrated that BT exerted synergistic antimicrobial and anti-biofilm effects when combined with COL against MDR organisms, especially COL-R GNB, in vitro and in vivo. The findings thus provide a reference for the clinical response to the serious challenge of MDR GNB and the exploitation of the potential antibacterial activities of existing clinical non-antibacterial drugs.

Potential of Syzygnium polyanthum as Natural Food Preservative: A Review

Food preservation is one of the strategies taken to maintain the level of public health. Oxidation activity and microbial contamination are the primary causes of food spoilage. For health reasons, people prefer natural preservatives over synthetic ones. Syzygnium polyanthum is widely spread throughout Asia and is utilized as a spice by the community. S. polyanthum has been found to be rich in phenols, hydroquinones, tannins, and flavonoids, which are potential antioxidants and antimicrobial agents. Consequently, S. polyanthum presents a tremendous opportunity as a natural preservative. This paper reviews recent articles about S. polyanthum dating back to the year 2000. This review summarizes the findings of natural compounds presented in S. polyanthum and their functional properties as antioxidants, antimicrobial agents, and natural preservatives in various types of food.

Meta-Analysis of In Vitro Antimicrobial Capacity of Extracts and Essential Oils of Syzygium aromaticum, Citrus L. and Origanum L.: Contrasting the Results of Different Antimicrobial Susceptibility Methods

Diffusion methods, including agar disk-diffusion and agar well-diffusion, as well as dilution methods such as broth and agar dilution, are frequently employed to evaluate the antimicrobial capacity of extracts and essential oils (EOs) derived from Origanum L., Syzygium aromaticum, and Citrus L. The results are reported as inhibition diameters (IDs) and minimum inhibitory concentrations (MICs), respectively. In order to investigate potential sources of variability in antimicrobial susceptibility testing results and to assess whether a correlation exists between ID and MIC measurements, meta-analytical regression models were built using in vitro data obtained through a systematic literature search. The pooled ID models revealed varied bacterial susceptibilities to the extracts and in some cases, the plant species and methodology utilised impacted the measurements obtained (p < 0.05). Lemon and orange extracts were found to be most effective against E. coli (24.4 ± 1.21 and 16.5 ± 0.84 mm, respectively), while oregano extracts exhibited the highest level of effectiveness against B. cereus (22.3 ± 1.73 mm). Clove extracts were observed to be most effective against B. cereus and demonstrated the general trend that the well-diffusion method tends to produce higher ID (20.5 ± 1.36 mm) than the disk-diffusion method (16.3 ± 1.40 mm). Although the plant species had an impact on MIC, there is no evidence to suggest that the methodology employed had an effect on MIC (p > 0.05). The ID–MIC model revealed an inverse correlation (R2 = 47.7%) and highlighted the fact that the extract dose highly modulated the relationship (p < 0.0001). The findings of this study encourage the use of extracts and EOs derived from Origanum, Syzygium aromaticum, and Citrus to prevent bacterial growth. Additionally, this study underscores several variables that can impact ID and MIC measurements and expose the correlation between the two types of results.

Natural sanitizer potential of Cuminum cyminum and applicable approach for calculation of Kováts retention index of its compounds

The demand for natural agents instead of chemicals in terms of food and health safety is increasing day by day. This study aimed to investigate the potential of the methanolic extract of Cuminum cyminum (C. cyminum) in the fight against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus)and Candida (C. albicans). The chemical composition of the methanolic extract of C. cyminum was analyzed using GS-MS. Also, Kováts retention indices were calculated for the detected compounds using an applicable formula. The most basic substance was cuminic aldehyde (27.86%) and p-(Dimethoxymethyl)-isopropylbenze (18.32%). The Minimum Inhibitory Concentration (MIC) of the extract was 0.1 g/mL for S. aureus and C. albicans while it was > 0.1 for E. coli. Although the methanol extract of C. cyminum acts against all three microorganisms, the most lasting effect was on S. aureus, indicating that it can be recommended as a strong antibacterial disinfectant for S. aureus.

Antibacterial activity of medicinal plants in Indonesia on Streptococcus pneumoniae

Streptococcus pneumoniae is a human pathogenic bacterium able to cause invasive pneumococcal diseases. Some studies have reported medicinal plants having antibacterial activity against pathogenic bacteria. However, antibacterial studies of medicinal plants against S. pneumoniae remains limited. Therefore, this study aims to describe the antibacterial activity of medicinal plants in Indonesia against S. pneumoniae. Medicinal plants were extracted by maceration with n-hexane, ethanol, ethyl acetate and water. Antibacterial activity was defined by inhibition zone and minimum inhibitory concentration (MIC). Bactericidal activity was measured by culture and time-killing measurement. Methods used to describe the mechanism of action of the strongest extract were done by absorbance at 595 nm, broth culture combined with 1% crystal violet, qRT-PCR targeting lytA, peZT and peZA, and transmission electron microscope to measure bacterial lysis, antibiofilm, LytA and peZAT gene expression, and ultrastructure changes respectively. Among 13 medicinal plants, L. inermis Linn. ethyl acetate extract showed the strongest antibacterial activity against S. pneumoniae with an MIC value of 0,16 mg/ml. Bactericidal activity was observed at 0,16 mg/ml for 1 hour incubation. Lawsonia inermis extract showed some mechanism of actions including bacterial lysis, antibiofilm, and ultrastructure changes such as cell wall disruption, decreasing cell membrane integrity and morphological disorder. Increasing of lytA and decreasing of peZA and peZT expression were also observed after incubation with the extract. In addition, liquid chromatography mass spectrophotometer showed phenolic compounds as the commonest compound in L. inermis ethyl acetate extract. This study describes the strong antibacterial activity of L. inermis with various mechanism of action including ultrastructure changes.

Toxicity and modulation of silver nanoparticles synthesized using abalone viscera hydrolysates on bacterial community in aquatic environment

Polysaccharide decorated silver nanoparticles (AgNPs) are a new type of antibacterial agent in aquaculture, but their effects on the bacterial community structure in aquaculture water are still unknown. In this study, the primary hydrolysate from abalone (Haliotis discus hannai) viscera (AVH) was used to biosynthesize AVH-AgNPs by in situ reduction, and the crystallinity nature, size, morphology, and chemical composition were analyzed by high-resolution characterization techniques such as Ultraviolet–visible spectroscopy (UV–vis), X-rays diffraction (XRD), Transmission Electron Microscope (TEM), Dynamic light scattering (DLS), Zeta potential, inductively coupled plasma-optical emission spectrometry (ICP-OES) and Turbiscan stability index (TSI) values. Furthermore, the acute toxicity of AVH-AgNPs to zebrafish (Danio rerio) and their effects on bacterial community structure in fish culture water at low concentrations were studied. The results showed that the spherical AVH-AgNPs with an average diameter of 54.57 ± 12.96 nm had good stability, low toxicity, and good in vitro antibacterial activity. Within the experimental concentration range, all AVH-AgNPs treatments had decreased the bacterial diversity in zebrafish culture water to varying degrees. The bacteria with significantly decreased abundances were pathogenic or potential pathogenic, such as Aeromonas veronii, Flavobacterium columnare, and genera Flectobacillus and Bosea. The abundance of Haliscomenobacter sp. JS224, which might cause sludge swelling, also decreased significantly. On the other hand, the relative abundance of some bacterial taxa could remove xenobiotics (e.g., Runella defluvii and Phenylobacterium), control water eutrophication (Sediminibacterium), and reduce toxic algae proliferation (Candidatus Intestinusbacter nucleariae and Candidatus Finniella), increased significantly. Thus, the application of AVH-AgNPs in aquaculture water at low concentrations is relatively safe and has positive significance for improving the aquaculture environment. Also, AVH-AgNPs have good prospects in aquaculture.

Traditional uses, pharmacological activities, and phytochemical constituents of the genus Syzygium: A review

The genus Syzygium comprises 1200-1800 species that belong to the family of Myrtaceae. Moreover, plants that are belonged to this genus are being used in the traditional system of medicine in Asian countries, especially in China, India, and Bangladesh. The aim of this review is to describe the scientific works and to provide organized information on the available traditional uses, phytochemical constituents, and pharmacological activities of mostly available species of the genus Syzygium in Bangladesh. The information related to genus Syzygium was analytically composed from the scientific databases, including PubMed, Google Scholar, Science Direct, Web of Science, Wiley Online Library, Springer, Research Gate link, published books, and conference proceedings. Bioactive compounds such as flavanone derivatives, ellagic acid derivatives and other polyphenolics, and terpenoids are reported from several species of the genus Syzygium. However, many members of the species of the genus Syzygium need further comprehensive studies regarding phytochemical constituents and mechanism-based pharmacological activities.

Green synthesis of walnut shell hydrochar, its antimicrobial activity and mechanism on some pathogens as a natural sanitizer

Hydrochar of waste walnut shells (WSH) was synthesized in the eco-friendly subcritical water medium (SWM) and its potential to fight against Klebsiella pneumoniae (K. pneumoniae), Staphylococcus aureus (S. aureus), Candida albicans (C. albicans) and Candida parapsilosis (C. parapsilosis) was investigated. Minimum Inhibitory Concentration (MIC) values of the WSH were 3.01 g/mL, 2.06 g/mL, 1.95 g/mL, and 3.12 g/mL for K. pneumoniae, S. aureus, C. albicans and C. parapsilosis, respectively. Survival of the pathogens was investigated by 3 min surface disinfection test exposure to WSH. While the highest inhibition was seen for C. parapsilosis (96.67%) on paper surface with 0.3 g/mL of bovine serum albumin (BSA), the lowest inhibition was determined for C. albicans (6.44%) on the plastic glass surface with 3 g/mL of BSA. An increase in protein, DNA, and potassium ion (K⁺) leakage was observed after microorganisms were incubated with WSH. This study provided an experimental basis for the practical application of WSH as a natural sanitizer agent.

Preliminary Insight of Pyrrolylated-Chalcones as New Anti-Methicillin-Resistant Staphylococcus aureus (Anti-MRSA) Agents

Bacterial infections are regarded as one of the leading causes of fatal morbidity and death in patients infected with diseases. The ability of microorganisms, particularly methicillin-resistant Staphylococcus aureus (MRSA), to develop resistance to current drugs has evoked the need for a continuous search for new drugs with better efficacies. Hence, a series of non-PAINS associated pyrrolylated-chalcones (1–15) were synthesized and evaluated for their potency against MRSA. The hydroxyl-containing compounds (8, 9, and 10) showed the most significant anti-MRSA efficiency, with the MIC and MBC values ranging from 0.08 to 0.70 mg/mL and 0.16 to 1.88 mg/mL, respectively. The time-kill curve and SEM analyses exhibited bacterial cell death within four hours after exposure to 9, suggesting its bactericidal properties. Furthermore, the docking simulation between 9 and penicillin-binding protein 2a (PBP2a, PDB ID: 6Q9N) suggests a relatively similar bonding interaction to the standard drug with a binding affinity score of −7.0 kcal/mol. Moreover, the zebrafish model showed no toxic effects in the normal embryonic development, blood vessel formation, and apoptosis when exposed to up to 40 µM of compound 9. The overall results suggest that the pyrrolylated-chalcones may be considered as a potential inhibitor in the design of new anti-MRSA agents.

Antibacterial and anti-biofilm activities of paeonol against Klebsiella pneumoniae and Enterobacter cloacae

Paeonol, the active ingredient of Paeonia lactiflora root bark, is widely used in traditional Chinese medicine. Few studies have reported the antibacterial activity of paeonol against bacterial pathogens. In this study, the antibacterial and anti-biofilm performance of paeonol against Klebsiella pneumoniae and Enterobacter cloacae was investigated as well as its mechanisms of action. Paeonol effectively inhibited the growth of K. pneumoniae and E. cloacae with a minimum inhibitory concentration of 64 μg ml^-1 and it was shown to disrupt the integrity of bacterial cell membranes, and alter cell morphology. Moreover, paeonol exhibited a potent inhibitory effect against adhesion and biofilm formation by K. pneumoniae and E. cloacae. In particular, paeonol efficiently compromised cells within biofilms, and dispersed mature biofilms. Therefore, the present study suggests that paeonol is a promising alternative antibacterial and anti-biofilm agent for combating infections caused by planktonic and biofilm cells of K. pneumoniae and E. cloacae.

Disrupting Irreversible Bacterial Adhesion and Biofilm Formation with an Engineered Enzyme

Biofilm formation is often attributed to postharvest bacterial persistence on fresh produce and food handling surfaces. In this study, a predicted glycosyl hydrolase enzyme was expressed, purified, and validated for the removal of microbial biofilms from biotic and abiotic surfaces under conditions used for chemical cleaning agents. Crystal violet biofilm staining assays revealed that 0.1 mg/ml of enzyme inhibited up to 41% of biofilm formation by Escherichia coli O157:H7, E. coli 25922, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes. Furthermore, the enzyme was effective at removing mature biofilms, providing a 35% improvement over rinsing with a saline solution alone. Additionally, a parallel-plate flow cell was used to directly observe and quantify the impact of enzyme rinses on E. coli O157:H7 cells adhering to spinach leaf surfaces. The presence of 1 mg/liter enzyme resulted in nearly 6-times-higher detachment rate coefficients than a deionized (DI) water rinse, while the total cells removed from the surface increased from 10% to 25% over the 30-min rinse time, reversing the initial phases of biofilm formation. Enzyme treatment of all 4 cell types resulted in significantly reduced cell surface hydrophobicity and collapse of negatively stained E. coli 25922 cells imaged by electron microscopy, suggesting potential polysaccharide surface modification of enzyme-treated bacteria. Collectively, these results point to the broad substrate specificity and robustness of the enzyme for different types of biofilm stages, solution conditions, and pathogen biofilm types and may be useful as a method for the removal or inhibition of bacterial biofilm formation. IMPORTANCE In this study, the ability of an engineered enzyme to reduce bacterial adhesion and biofilm formation of several foodborne pathogens was demonstrated, representing a promising option for enhancing or replacing chlorine and other chemical sanitizers in food processing applications. Specifically, significant reductions of biofilms of the pathogens Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes are observed, as are reductions in initial adhesion. Enzymes have the added benefits of being green, sustainable alternatives to chemical sanitizers, as well as having a minimal impact on food properties, in contrast to many alternative antimicrobial options such as bleach that aim to minimize food safety risks.

Antibacterial Activity of Arbutus pavarii Pamp against Methicillin-Resistant Staphylococcus aureus (MRSA) and UHPLC-MS/MS Profile of the Bioactive Fraction

Arbutus pavarii Pamp is a medicinal plant commonly used by local tribes in East Libya for the treatment of many diseases, such as gastritis, renal infections, cancer and kidney diseases. In this study, the antibacterial activity of the leaf and stem bark extracts of the plant against methicillin-resistant Staphylococcus aureus (MRSA), as well as the metabolite profiles of the bioactive fractions, was investigated. The antibacterial activity was determined by disc diffusion method, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), while the microbial reduction by the bioactive fraction was evaluated using time-kill test. The bioactive fraction was further subjected to ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-ESI-MS/MS) analysis to putatively identify the chemical constituents contained therein. All the extracts and fractions showed different levels of antibacterial activity on the tested MRSA strains. The highest total antibacterial activity, i.e., 4007.6 mL/g, was exhibited by the crude leaf methanolic extract. However, the ethyl acetate fraction of the leaf showed moderate to significant antibacterial activity against MRSA at low MIC (0.08-1.25 mg/mL). Metabolite profiling of this fraction using UHPLC-ESI-MS/MS resulted in the putative identification of 28 compounds, which included phenolic acids, flavan-3-ols and flavonols. The results of this study showed that the ethyl acetate fraction of Arbutus pavarii leaf possessed potential antibacterial activity against MRSA and hence can be further explored for pharmaceutical applications as a natural antibacterial agent.

Chemical Composition and Bioactivities of Essential Oil from Leaves of Syzygium cumini (L.) Skeels Native to Punjab, Pakistan

Herbal medicines are widely used for the treatment of different types of diseases like skin and throat infections and other diseases in developing countries. Syzygium cumini (L.) Skeels fruit, leaves and bark were used for the remedies of different diseases anciently. The aim of the present study was to evaluate the chemical profile of Syzygium cumini leaves essential oil (EO) from Punjab, Pakistan. The essential oil was isolated using hydrodistillation technique and analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). Free radical scavenging capacity and antioxidant activity were assessed by using DPPH radical scavenging ability, inhibition of linoleic acid peroxidation, bleaching of β-carotene in linoleic acid system and reducing power assays. Antimicrobial potential was assessed by disc diffusion assay and measurement of minimum inhibitory concentration (MIC) using resazurin microtiter-plate assay. The anti-heme biocrystallization activity of EO was also assessed. The major components (>3%) found in Syzygium cumini leaves EO were β-farnesene (3.42 %), caryophyllenol (3.46 %), terpinen-4-ol (3.61 %), β-myrcene (3.90 %), γ-cadinene (4.09 %), fenchol (4.22 %), cis-β-ocimene (4.40 %) and 5-methyl-1,3,6-heptatriene (4.90 %). Excellent antioxidant, antimicrobial and weak antimalarial potential was observed. It can be concluded that Syzygium cumini leaves EO has potential application for food and pharmaceutical industries.

Susceptibility Assessment of Multidrug Resistant Bacteria to Natural Products

Objective:

The aim of this study was to examine the effect of some natural compounds against multidrug-resistant bacteria.

Methods:

Forty-three bacterial strains were collected. Disc diffusion and minimum inhibitory concentration (MIC) tests were carried out for natural compounds including quercetin, Acacia nilotica, Syzygium aromaticum, and Holothuria atra. Scanning electron microscope analysis and bacterial DNA apoptosis assays were performed.

Results:

Staphylococcus aureus strains were resistant to imipenim, ampicillin, and penicillin. Most Escherichia coli strains were resistant to amoxicillin, clavulanat, and ampicillin. Finally, tigecycline was effective with Klebsiella pneumoniae and was resistant to all antibiotics. Only S aromaticum had an antibacterial effect on K pneumoniae. Most S aureus strains were sensitive to S aromaticum, A nilotica, and quercetin. All examined natural extracts had no effect on E coli. Holothuria atra had no effect on any of the strains tested. Minimum inhibitory concentration and minimum bactericidal concentration values for examined plants against S aureus were 6.25 to 12, 1.6 to 3.2, and 9.12 to 18.24 mg/mL, respectively. Syzygium aromaticum was active against K pneumoniae with an MIC of 12.5 mg/mL. Scanning electron microscope analysis performed after 24 and 48 hours of incubation showed bacterial strains with distorted shapes and severe cell wall damage. Syzygium aromaticum, quercetin, and A nilotica showed clear fragmentations of S aureus DNA.

Conclusions:

Current findings confirmed the beneficial effect of using natural products such as clove (S aromaticum), quercetin, and A nilotica as a promising therapy to overcome multidrug resistant bacteria.

Plant Phenolics and Phenolic-Enriched Extracts as Antimicrobial Agents against Food-Contaminating Microorganisms

Phenolic compounds and extracts with bioactive properties can be obtained from many kinds of plant materials. These natural substances have gained attention in the food research as possible growth inhibitors of foodborne pathogenic and spoilage bacteria. Many phenolic-enriched plant extracts and individual phenolics have promising anti-quorum sensing potential as well and can suppress the biofilm formation and toxin production of food-related pathogens. Various studies have shown that plant phenolics can substitute or support the activity of synthetic food preservatives and disinfectants, which, by the way, can provoke serious concerns in consumers. In this review, we will provide a brief insight into the bioactive properties, i.e., the antimicrobial, anti-quorum sensing, anti-biofilm and anti-enterotoxin activities, of plant phenolic extracts and compounds, with special attention to pathogen microorganisms that have food relation. Carbohydrase aided applications to improve the antimicrobial properties of phenolic extracts are also discussed.

Roles of three TonB systems in the iron utilization and virulence of the Aeromonas hydrophila Chinese epidemic strain NJ-35

The TonB system functions in iron transport and has been identified in certain Gram-negative bacteria. Recently, we reported three TonB systems in the Aeromonas hydrophila Chinese epidemic strain NJ-35, but the functions of these systems have not been thoroughly elucidated to date. In this study, we investigated the role of these TonB systems in A. hydrophila iron utilization and virulence. We found that tonB1 and tonB2 were preferentially transcribed in iron-chelated conditions, where gene expression levels were approximately 8- and 68-fold higher compared with iron-rich conditions, respectively; tonB3 was consistently transcribed at a low level under iron-repleted and iron-depleted conditions. Only the TonB2 system was required to utilize iron-binding proteins. The tonB123 mutant showed increased susceptibility to erythromycin and roxithromycin. In addition, all three tonB genes were involved in A. hydrophila virulence in zebrafish, and various phenotypes associated with environmental survival were changed with varying degrees in each tonB mutant. TonB2 plays a relatively major role in adhesion, motility, and biofilm formation, while TonB3 is more involved in the anti-phagocytosis of A. hydrophila. In each observed phenotype, no significant difference was found between the single- and double-deletion mutants, whereas the triple-deletion mutant exhibited the most serious defects, indicating that all three TonB systems of A. hydrophila coordinately complement one another. In conclusion, this study elucidates the importance of TonB in iron acquisition and virulence of A. hydrophila, which lays the foundation for future studies regarding the survival mechanisms of this bacterium in iron-restricted environments.

Antibacterial and cytotoxic activities of the Syzygium polyanthum leaf extract from Malaysia

Background and Aim:

The increasing prevalence of drug resistance eventually leads scientist to discover new drugs that could solve the problem. Since ancient immemorial times, medicinal plants generally known as herbs were widely used in every culture throughout the world. In fact, currently up to 70,000 plant species have been screened for biological activities and about 70% ends up for commercialization. Therefore, this study was aimed to evaluate the potential cytotoxic and antibacterial effect of Syzygium polyanthum leaves which are local Malaysia plants, against 4T1 and MCF-7 mammary carcinoma cells, respectively, and also against bacteria causing mastitis in cows.

Materials and Methods:

The cytotoxic effect of hydromethanolic extract of S. polyanthum against 4T1 and MCF-7 mammary carcinoma cells was evaluated using 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The cells were treated with the concentration of extracts ranging from 15.63 µg/mL to 1000 µg/ml for 72 h, and the percentage of cell survivability was determined based on minimum concentration that was able to allow at least 50% growth of cancer cells (IC₅₀) after 72 h. The antibacterial activity was tested against common bacteria causing mastitis in cow. The bacteria were isolated from milk samples. The antibacterial activity of the extract was determined by disk diffusion method and susceptibility test based on minimum inhibitory concentration (MIC).

Results:

Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcus intermedius were isolated from the milk samples that positive for mastitis. The MIC values range from 7.12 mm to 13.5 mm. The extract exhibits the widest zone of inhibition (13.5±0.20 mm) at 1000 mg/ml of concentrations. The extract relatively has low cytotoxicity effect against 4T1 and MCF-7 cells with IC₅₀ values ranging from 672.57±59.42 and 126.05±50.89 µg/ml, respectively.

Conclusion:

S. polyanthum exerts weak antibacterial activity and cytotoxic effect to mammary carcinoma cells. The extract does not toxic to cells. However, further study is recommended, especially, this plant should be tested for in vivo.