Antibacterial activities of naturally occurring compounds against antibiotic-resistant Bacillus cereus vegetative cells and spores, Escherichia coli, and Staphylococcus aureus

Tapping into Palm Sap: Insights into extraction practices, quality profiles, fermentation chemistry, and preservation techniques

The quality profile, extraction yield, and fermentation chemistry of palm sap depend on various factors such as extraction technique, weather conditions, and preservation methods. This review aims to provide a detailed overview of palm sap extraction techniques and the methods for its preservation. The compositional analysis of palm sap, including physical and chemical parameters such as sugar content, acidity, and mineral composition, is discussed thoroughly. The role of microorganisms in fermentation and the effects of various influencing factors are also critically examined. Additionally, this review evaluates different preservation methods, including thermal processes, refrigeration, and electrical techniques, highlighting their effectiveness in extending the shelf life of palm sap. The review further explores the emerging impact of nanotechnology on palm sap preservation, offering insights into the latest industry challenges, developments, and future prospects. By presenting these findings, this review aims to enhance the scientific understanding of palm sap and stimulate additional research and innovation in the field, paving the way for improved production practices and product quality.

Discovery of potential anti- Staphylococcus aureus natural products and their mechanistic studies using machine learning and molecular dynamic simulations

The structure-activity analysis (SAR) and machine learning were used to investigate potential anti-S. aureus agents in a faster method. In this study, 24 oxygenated benzene ring components with S. aureus inhibition capacity were confirmed by literature exploring and in-house experiments, and the SAR analysis suggested that the hydroxyl group position may affect the anti-S. aureus activity. The 2D-MLR-QSAR model with 9 descriptors was further evaluated as the best model among the 21 models. After that, hesperetic acid and 2-HTPA were further explored and evaluated as the potential anti-S. aureus agents screening in the natural product clustering library through the best QSAR model calculation. The antibacterial capacities of hesperetic acid and 2-HTPA had been investigated and proved the similar predictive pMIC value resulting from the QSAR model. Besides, the two novel components were able to inhibit the growth of S. aureus by disrupting the cell membrane through the molecular dynamics simulation (MD), which further evidenced by scanning electron microscopy (SEM) test and PI dye results. Overall, these results are highly suggested that QSAR can be used to predict the antibacterial agents targeting S. aureus, which provides a new paradigm to research the molecular structure-antibacterial capacity relationship.

Repression of Staphylococcus aureus and Escherichia coli by Lactiplantibacillus plantarum Strain AG10 in Drosophila melanogaster In Vivo Model

Probiotic bacteria exhibiting antagonistic activities against pathogenic bacteria are widely considered as potential options for the prevention and treatment of various infectious diseases and represent potential substitutes of antibiotics. Here we show that the L. plantarum AG10 strain represses the growth of Staphylococcus aureus and Escherichia coli in vitro and diminishes their negative effects in vivo in a Drosophila melanogaster model of survival on embryonic (larvae) and pupa stages. In an agar drop diffusion test, L. plantarum AG10 exhibited antagonistic properties against Escherichia coli, Staphylococcus aureus, Serratia marcescens and Pseudomonas aeruginosa, and repressed the growth of E. coli and S. aureus during milk fermentation. In a Drosophila melanogaster model, L. plantarum AG10 alone did not provide any significant effect, either during the embryonic stage or during further development of the flies. Despite this, it was able to restore the viability of groups infected with either E. coli and S. aureus, almost to the level of non-treated control at all stages of development (larvae, pupa and adult). Moreover, in the presence of L. plantarum AG10, pathogens-induced mutation rates and recombination events reduced 1.5-2-fold. The genome of L. plantarum AG10 was sequenced and deposited at NCBI under the accession number PRJNA953814 and consists of annotated genome and raw sequence data. It consists of 109 contigs and is 3,479,919 bp in length with a GC content of 44.5%. The analysis of the genome has revealed considerably few putative virulence factors and three genes responsible for the biosynthesis of putative antimicrobial peptides, with one of them exhibiting a high probability of antimicrobial properties. Taken together, these data allow the suggestion that the L. plantarum AG10 strain is promising for use in both dairy production and probiotics as a preservative from foodborne infections.

Exploring the binding mechanism of β-resorcylic acid with calf thymus DNA: Insights from multi-spectroscopic, thermodynamic and bioinformatics approaches

β-resorcylic acid (BR) is a phytochemical which is widely used in the food industry as a flavouring agent and preservative. It has also been found to exhibit antibacterial action against several types of food-borne bacteria. DNA is the main molecular target for many small molecules of therapeutic importance. Hence, the interest is rapidly growing among the researchers to elucidate the interaction between small molecules and DNA. Thus, paving the way to design novel DNA-specific drugs. In this study, an attempt was made to examine the mechanism of binding of BR with calf thymus DNA (ctDNA) with the help of various experiments based on spectroscopy and in silico studies. The spectroscopic studies like UV absorption and fluorescence affirmed the complex formation between BR and ctDNA. The observed binding constant was in the order of 10³ M^-1 which is indicative of the groove binding mechanism. These findings were further verified by dye-displacement assay, potassium iodide quenching, urea denaturation assay, the study of the effect of ssDNA, circular dichroism and DNA thermal denaturing studies. Different temperature-based fluorescence and isothermal titration calorimetry (ITC) experiments were employed to evaluate thermodynamic parameters. The analysis of thermodynamic parameters supports the enthalpically driven, exothermic and spontaneous nature of the reaction between BR and ctDNA. The forces involved in the binding process were mainly found to be hydrogen bonding, van der Waals and hydrophobic interactions. The results obtained from the molecular docking and molecular dynamics (MD) simulation were consistent with the in vitro experiments, which support the groove binding mode of BR with ctDNA.

Enteropathogenic Potential of Bacillus thuringiensis Isolates from Soil, Animals, Food and Biopesticides

Despite its benefits as biological insecticide, Bacillus thuringiensis bears enterotoxins, which can be responsible for a diarrhoeal type of food poisoning. Thus, all 24 isolates from foodstuffs, animals, soil and commercially used biopesticides tested in this study showed the genetic prerequisites necessary to provoke the disease. Moreover, though highly strain-specific, various isolates were able to germinate and also to actively move, which are further requirements for the onset of the disease. Most importantly, all isolates could grow under simulated intestinal conditions and produce significant amounts of enterotoxins. Cytotoxicity assays classified 14 isolates as highly, eight as medium and only two as low toxic. Additionally, growth inhibition by essential oils (EOs) was investigated as preventive measure against putatively enteropathogenic B. thuringiensis. Cinnamon Chinese cassia showed the highest antimicrobial activity, followed by citral, oregano and winter savory. In all tests, high strain-specific variations appeared and must be taken into account when evaluating the hazardous potential of B. thuringiensis and using EOs as antimicrobials. Altogether, the present study shows a non-negligible pathogenic potential of B. thuringiensis, independently from the origin of isolation. Generally, biopesticide strains were indistinguishable from other isolates. Thus, the use of these pesticides might indeed increase the risk for consumers’ health. Until complete information about the safety of the applied strains and formulations is available, consumers or manufacturers might benefit from the antimicrobial activity of EOs to reduce the level of contamination.

Synergistic staphylocidal interaction of benzoic acid derivatives (benzoic acid, 4-hydroxybenzoic acid and β-resorcylic acid) and capric acid: mechanism and verification study using artificial skin

Objectives

The present study was designed to investigate a synergistic staphylocidal interaction of antimicrobials.

Methods

The widely used preservative benzoic acid (BzA) and its derivatives [4-hydroxybenzoic acid (HA) and β-resorcylic acid (β-RA)] combined with capric acid (CPA) were investigated.

Results

β-RA was identified as the most effective antimicrobial exhibiting synergistic action with CPA against both Staphylococcus aureus and MRSA. For example, a complete reduction of bacteria (>7.3 log reduction) was obtained within 5 min after treatment with 5.0 mM β-RA (0.079%) plus 0.20 mM CPA (0.004%), while treatment with each material individually showed low bactericidal effects (<1.5 log reduction). Flow cytometry analysis identified membrane disruption related to the synergistic mechanisms, including the following: (i) membrane disruption by CPA (69.2% of cells were damaged by 0.20 mM CPA treatment); (ii) antimicrobial entry through the damaged membrane; and (iii) cytoplasmic ion imbalance resulting in cell death. We verified that the synergistic combination was also effective against MRSA on artificial skin (99.989% elimination after 5 min).

Conclusions

We used only consumer-preferred natural-borne antimicrobials and a very small amount of material was needed based on the synergistic effects. Therefore, these antimicrobials can be widely used as alternative anti-MRSA compounds in healthcare products, cosmetics, pharmaceutical products, foods and for environmental hygiene.

Anti-borreliae efficacy of selected organic oils and fatty acids

BACKGROUND

Borrelia sp. is a causative pathogen of Lyme disease which has become a worldwide health concern. Non-toxic approaches especially directed toward latent persistent forms of this pathogen are desired. Lipids in the form of volatile and non-volatile oils, and fatty acids with proven anti-borreliae efficacy could become an additional support or an alternative for consideration in treatment approaches.

METHODS

In this study we investigated 47 lipids (30 volatile and non-volatile oils, and 17 fatty acids) of plant and animal origin against typical motile, knob/round-shaped persisters, and biofilm-like aggregates of Borrelia burgdorferi s.s. and Borrelia garinii, which are identified as pathogenic factors of Lyme disease in the USA and Europe, using direct microscopic counting and spectrofluorometric measurements.

RESULTS

Out of all examined lipids, 5 oils (Bay leaf oil, Birch oil, Cassia oil, Chamomile oil German, and Thyme oil) at or below 0.25%, and 3 fatty acids (13Z,16Z Docosadienoic acid, erucic acid, and petroselinic acid) at or below 0.75 mg/ml, showed bactericidal activity against typical motile spirochetes and knob/round-shaped persisters. Only Bay leaf oil and Cassia oil, including their major constituents, eugenol and cinnamaldehyde, showed to target biofilm-like aggregates of both tested Borrelia spp. at the same concentration, although with 20-30% eradication mark.

CONCLUSION

Based on obtained results, volatile oils were more potent than non-volatile oils, and unsaturated fatty acids were more effective than saturated fatty acids. Among all tested oils, Bay leaf oil and Cassia oil, with their major components eugenol and cinnamaldehyde, seem to have the highest anti-borreliae efficacy.

Synthesis and Evaluation of Antimicrobial and Antibiofilm Properties of A-Type Procyanidin Analogues against Resistant Bacteria in Food

Natural A-type procyanidins have shown very interesting biological activities, such as their proven antiadherence properties against pathogenic bacteria. In order to find the structural features responsible for their activities, we describe herein the design and synthesis of six A-type procyanidin analogues and the evaluation of their antimicrobial and antibiofilm properties against 12 resistant bacteria, both Gram positive and Gram negative, isolated from organic foods. The natural A-type procyanidin A-2, which had known antiadherence activity, was also tested as a reference compound for the comparative studies. Within the series, analogue 4, which had a NO₂ group on ring A, showed the highest antimicrobial activity (MIC of 10 μg/mL) and was one of the best molecules at preventing biofilm formation (up to 40% decreases at 100 μg/mL) and disrupting preformed biofilms (up to 40% reductions at 0.1 μg/mL). Structure-activity relationships are also analyzed.

Enhanced silver loaded antibacterial titanium implant coating with novel hierarchical effect

In this study, we present a novel strategy for hierarchical antibacterial implant coating by controlling structural and componential features as regulators of surface bactericidal property. Anodized titanium dioxide nanotubes and self-polymerized polydopamine were both used as preliminary antibacterial agents with a significant positive effect on surface bioactivity. At the same time, the storage capacity of nanotubes and the in situ reduction activity of polydopamine can introduce large amounts of strong attached silver nanoparticles for enhanced stable antibacterial performance. The surface morphology, chemical composition, and hydrophilicity had been thoroughly characterized. The sustained silver release performances were continuously monitored. The successively in vitro inhibition on Staphylococcus aureus growth of titanium dioxide nanotube, polydopamine layer and silver nanoparticles demonstrated the hierarchical antibacterial property of the final silver nanoparticles-incorporated polydopamine-modified titanium dioxide nanotube coating (silver/polydopamine/nanotube). Moreover, the bioactivity investigation indicated the vital role of polydopamine-modified titanium dioxide nanotube coating on preserving healthy osteoblast activity at the implant interface. The unique hierarchical coating for titanium implant may be a promising method to maximize antibacterial capacity and maintain good cellular activity at the same time.

Mechanisms of Antimicrobial Action of Cinnamon and Oregano Oils, Cinnamaldehyde, Carvacrol, 2,5-Dihydroxybenzaldehyde, and 2-Hydroxy-5-Methoxybenzaldehyde against Mycobacterium avium subsp. paratuberculosis (Map)

The antimicrobial modes of action of six naturally occurring compounds, cinnamon oil, cinnamaldehyde, oregano oil, carvacrol, 2,5-dihydroxybenzaldehyde, and 2-hydroxy-5-methoxybenzaldehyde, previously found to inhibit the growth of Mycobacterium avium subsp. paratuberculosis (Map) reported to infect food animals and humans and to be present in milk, cheese, and meat, were investigated. The incubation of Map cultures in the presence of all six compounds caused phosphate ions to leak into the extracellular environment in a time- and concentration-dependent manner. Cinnamon oil and cinnamaldehyde decreased the intracellular adenosine triphosphate (ATP) concentration of Map cells, whereas oregano oil and carvacrol caused an initial decrease of intracellular ATP concentration that was restored gradually after incubation at 37 °C for 2 h. Neither 2,5-dihydroxybenzaldehyde nor 2-hydroxy-5-methoxybenzaldehyde had a significant effect on intracellular ATP concentration. None of the compounds tested were found to cause leakage of ATP to the extracellular environment. Monolayer studies involving a Langmuir trough apparatus revealed that all anti-Map compounds, especially the essential oil compounds, altered the molecular packing characteristics of phospholipid molecules of model membranes, causing fluidization. The results of the physicochemical model microbial membrane studies suggest that the destruction of the pathogenic bacteria might be associated with the disruption of the bacterial cell membrane.

β-Resorcylic Acid, a Phytophenolic Compound, Reduces Campylobacter jejuni in Postharvest Poultry

Human Campylobacter infections, a leading foodborne illness globally, has been linked with the high prevalence of this bacterium on raw retail chicken products. Reduction of Campylobacter counts on poultry products would greatly reduce the risk of subsequent infections in humans. To this end, this study investigated the potential of the phytophenolic compound β-resorcylic acid (BR) to reduce Campylobacter counts on postharvest poultry (chicken skin or meat). Four trials in total, two each on thigh skin or breast meat, were conducted in which chicken skin or meat samples (2 ± 0.1 g; 10 samples per treatment) were inoculated with 50 μL (∼10⁶ CFU per sample) of a cocktail of four wild strains of C. jejuni. After 30 min of attachment, inoculated samples were dipped in a 0, 0.5, 1, or 2% BR solution for 30 s immediately followed by vigorously vortexing the samples in Butterfield's phosphate diluent and plating the supernatant for Campylobacter enumeration. In addition, the effect of BR on the color of skin and meat samples was studied. Moreover, the change in the expression of survival and virulence genes of C. jejuni exposed to BR was evaluated. Data were analyzed by the PROC MIXED procedure of SAS (P < 0.05; SAS Institute Inc., Cary, NC). All BR treatments significantly reduced Campylobacter populations on both chicken or meat samples by 1 to 3 log CFU/g compared with non-BR-treated washed controls. No significant difference in the lightness, redness, and yellowness of skin and meat samples was observed on exposure to BR wash (P > 0.05). Real-time PCR results revealed that BR treatment down-regulated expression of select genes coding for motility (motA, motB) and attachment (cadF, ciaB) in the majority of C. jejuni strains. Stress response genes (sodB, katA) were upregulated in C. jejuni S-8 (P < 0.05). Overall, our results suggest that BR could be effectively used as antimicrobial dip treatment during poultry processing for reducing Campylobacter on chicken carcasses.

Virulence Factors and Antibiotic Susceptibility of Staphylococcus aureus Isolates in Ready-to-Eat Foods: Detection of S. aureus Contamination and a High Prevalence of Virulence Genes

Staphylococcus aureus is one of the leading causes of food poisoning. Its pathogenicity results from the possession of virulence genes that produce different toxins which result in self-limiting to severe illness often requiring hospitalization. In this study of 200 sushi and sashimi samples, S. aureus contamination was confirmed in 26% of the food samples. The S. aureus isolates were further characterized for virulence genes and antibiotic susceptibility. A high incidence of virulence genes was identified in 96.2% of the isolates and 20 different virulence gene profiles were confirmed. DNA amplification showed that 30.8% (16/52) of the S. aureus carried at least one SE gene which causes staphylococcal food poisoning. The most common enterotoxin gene was seg (11.5%) and the egc cluster was detected in 5.8% of the isolates. A combination of hla and hld was the most prevalent coexistence virulence genes and accounted for 59.6% of all isolates. Antibiotic resistance studies showed tetracycline resistance to be the most common at 28.8% while multi-drug resistance was found to be low at 3.8%. In conclusion, the high rate of S. aureus in the sampled sushi and sashimi indicates the need for food safety guidelines.

Antibiotic-resistant bacteria: prevalence in food and inactivation by food-compatible compounds and plant extracts

Foodborne antibiotic-resistant pathogenic bacteria such as Campylobacter jejuni, Bacillus cereus, Clostridium perfringens, Escherichia coli, Salmonella enterica, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahemolyticus can adversely affect animal and human health, but a better understanding of the factors involved in their pathogenesis is needed. To help meet this need, this overview surveys and interprets much of our current knowledge of antibiotic (multidrug)-resistant bacteria in the food chain and the implications for microbial food safety and animal and human health. Topics covered include the origin and prevalence of resistant bacteria in the food chain (dairy, meat, poultry, seafood, and herbal products, produce, and eggs), their inactivation by different classes of compounds and plant extracts and by the use of chlorine and physicochemical methods (heat, UV light, pulsed electric fields, and high pressure), the synergistic antimicrobial effects of combinations of natural antimicrobials with medicinal antibiotics, and mechanisms of antimicrobial activities and resistant effects. Possible areas for future research are suggested. Plant-derived and other safe natural antimicrobial compounds have the potential to control the prevalence of both susceptible and resistant pathogens in various environments. The collated information and suggested research will hopefully contribute to a better understanding of approaches that could be used to minimize the presence of resistant pathogens in animal feed and human food, thus reducing adverse effects, improving microbial food safety, and helping to prevent or treat animal and human infections.

Chemistry and multibeneficial bioactivities of carvacrol (4-isopropyl-2-methylphenol), a component of essential oils produced by aromatic plants and spices

Aromatic plants produce organic compounds that may be involved in the defense of plants against phytopathogenic insects, bacteria, fungi, and viruses. One of these compounds, called carvacrol, which is found in high concentrations in essential oils such as oregano, has been reported to exhibit numerous bioactivities in cells and animals. This integrated overview surveys and interprets our present knowledge of the chemistry and analysis of carvacrol and its beneficial bioactivities. These activities include its antioxidative properties in food (e.g., lard, sunflower oil) and in vivo and the inhibition of foodborne and human antibiotic-susceptible and antibiotic-resistant pathogenic bacteria, viruses, pathogenic fungi and parasites, and insects in vitro and in human foods (e.g., apple juice, eggs, leafy greens, meat and poultry products, milk, oysters) and food animal feeds and wastes. Also covered are inhibitions of microbial and fungal toxin production and the anti-inflammatory, analgesic, antiarthritic, antiallergic, anticarcinogenic, antidiabetic, cardioprotective, gastroprotective, hepatoprotective, and neuroprotective properties of carvacrol as well as metabolic, synergistic, and mechanistic aspects. Areas for future research are also suggested. The collated information and suggested research might contribute to a better understanding of agronomical, biosynthetic, chemical, physiological, and cellular mechanisms of the described health-promoting effects of carvacrol, and facilitate and guide further studies needed to optimize the use of carvacrol as a multifunctional food in pure and encapsulated forms, in edible antimicrobial films, and in combination with plant-derived and medical antibiotics to help prevent or treat animal and human diseases.

Effect of structure on the interactions between five natural antimicrobial compounds and phospholipids of bacterial cell membrane on model monolayers

Monolayers composed of bacterial phospholipids were used as model membranes to study interactions of the naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, and the plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol, previously found to be active against both Gram-positive and Gram-negative pathogenic microorganisms. The lipid monolayers consist of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexa- decanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and 1,1',2,2'-tetratetradecanoyl cardiolipin (cardiolipin). Surface pressure–area (π-A) and surface potential–area (Δψ-A) isotherms were measured to monitor changes in the thermodynamic and physical properties of the lipid monolayers. Results of the study indicated that the five compounds modified the three lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial –lipid complexes, reducing the packing effectiveness of the lipids, increasing the membrane fluidity, and altering the total dipole moment in the monolayer membrane model. The interactions of the five antimicrobial compounds with bacterial phospholipids depended on both the structure of the antimicrobials and the composition of the monolayers. The observed experimental results provide insight into the mechanism of the molecular interactions between naturally-occurring antimicrobial compounds and phospholipids of the bacterial cell membrane that govern activities.

Expression, crystallization and preliminary X-ray crystallographic analysis of peptide deformylase from Campylobacter jejuni

Campylobacter jejuni is one of the major foodborne pathogens causing human infection. Peptide deformylase, a metallohydrolase, catalyzes the deformylation of N-formylated methionine in newly synthesized polypeptides in prokaryotes and some eukaryotic organelles. The deformylation process is an essential step in protein synthesis and has attracted much attention as a potential target for the development of novel antibacterial agents. Here, the cloned codon-optimized def gene from C. jejuni was synthesized and the protein was expressed, purified and crystallized. C. jejuni peptide deformylase crystals obtained at pH 7.0 and pH 6.5 diffracted to 2.9 Å resolution and belonged to the trigonal space group R3, with unit-cell parameters a=b=105.7, c=58.0 Å. One monomer existed in the asymmetric unit, with a corresponding VM of 3.1 Å3 Da(-1) and a solvent content of 60.4%.

Use of plant-derived antimicrobials for improving the safety of poultry products

Salmonella Enteritidis and Campylobacter jejuni are the 2 major foodborne pathogens transmitted through poultry products. Chickens are the reservoir hosts of these pathogens, with their intestinal colonization being the most significant factor causing contamination of meat and eggs. Effective preslaughter strategies for reducing the colonization of birds with these pathogens are critical to improve the microbiological safety of poultry products. An antimicrobial treatment that can be applied through feed represents the most practical and economically viable method for adoption on farms. Additionally, a natural and safe antimicrobial will be better accepted by producers without concerns for toxicity. This symposium talk discussed the potential use of plant-derived, GRAS (generally recognized as safe)-status molecules, caprylic acid, trans-cinnamaldehyde, eugenol, carvacrol, and thymol as feed supplements for reducing cecal populations of Salmonella Enteritidis and C. jejuni in chickens. Additionally, the effect of plant molecules on Salmonella virulence genes critical for cecal colonization in chickens was also discussed.

Bactericidal activities of health-promoting, food-derived powders against the foodborne pathogens Escherichia coli, Listeria monocytogenes, Salmonella enterica, and Staphylococcus aureus

We evaluated the relative bactericidal activities (BA(50) ) of 10 presumed health-promoting food-based powders (nutraceuticals) and, for comparison, selected known components against the following foodborne pathogens: Escherichia coli O157:H7, Salmonella enterica, Listeria monocytogenes, and Staphylococcus aureus. The relative activities were evaluated using quantitative bactericidal activity [(BA(50) value, defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in colony forming units]. The BA(50) values were determined by fitting the data to a sigmoidal curve by regression analysis using concentration-antimicrobial response data. Antimicrobial activity is indicated by a low BA(50) value; meaning less material is needed to kill 50% of the bacteria. Olive pomace, olive juice powder, and oregano leaves were active against all 4 pathogens, suggesting that they behave as broad-spectrum antimicrobials. All powders exhibited strong antimicrobial activity against S. aureus. The following powders showed exceptionally high activity against S. aureus (as indicated by the low BA(50) values shown in parentheses): apple skin extract (0.002%); olive pomace (0.008%); and grape seed extract (0.016%). Listeria bacteria were also highly susceptible to apple skin extract (0.007%). The most active substances provide candidates for the evaluation of antimicrobial effectiveness in human food and animal feed.

PRACTICAL APPLICATION

Plant-derived health-promoting food supplements, high in bioactive compounds, are candidates for use as antimicrobials in food.

The olive compound 4-hydroxytyrosol inactivates Staphylococcus aureus bacteria and Staphylococcal Enterotoxin A (SEA)

The foodborne pathogen Staphylococcus aureus produces the virulent staphylococcal enterotoxin A (SEA), a single chain protein which consists of 233 amino acid residues with a molecular weight of 27078 Da. SEA is a superantigen that is reported to contribute to animal (mastitis) and human (emesis, diarrhea, atopic dermatitis, arthritis, and toxic shock) syndromes. Changes in the native structural integrity may inactivate the toxin by preventing molecular interaction with cell membrane receptor sites of their host cells. In the present study, we evaluated the ability of the pure olive compound 4-hydroxytyrosol and a commercial olive powder called Hidrox-12, prepared by freeze-drying olive juice, to inhibit S. aureus bacteria and SEA's biological activity. Dilutions of both test substances inactivated the pathogens. Two independent cell assays (BrdU incorporation into newly synthesized DNA and glycyl-phenylalanyl-aminofluorocoumarin proteolysis) demonstrated that the olive compound 4-hydroxytyrosol also inactivated the biological activity of SEA at concentrations that were not toxic to the spleen cells. However, efforts to determine inhibition of the toxin by Hidrox-12 were not successful because the olive powder was cytotoxic to the spleen cells at concentrations found to be effective against the bacteria. The results suggest that food-compatible and safe antitoxin olive compounds can be used to inactivate both pathogens and toxins produced by the pathogens. Practical Application:  The results of this study suggest that food-compatible and safe antitoxin olive compounds can be used to reduce both pathogens and toxins produced by the pathogens in foods.

Statistical metamodeling for revealing synergistic antimicrobial interactions

Many bacterial pathogens are becoming drug resistant faster than we can develop new antimicrobials. To address this threat in public health, a metamodel antimicrobial cocktail optimization (MACO) scheme is demonstrated for rapid screening of potent antibiotic cocktails using uropathogenic clinical isolates as model systems. With the MACO scheme, only 18 parallel trials were required to determine a potent antimicrobial cocktail out of hundreds of possible combinations. In particular, trimethoprim and gentamicin were identified to work synergistically for inhibiting the bacterial growth. Sensitivity analysis indicated gentamicin functions as a synergist for trimethoprim, and reduces its minimum inhibitory concentration for 40-fold. Validation study also confirmed that the trimethoprim-gentamicin synergistic cocktail effectively inhibited the growths of multiple strains of uropathogenic clinical isolates. With its effectiveness and simplicity, the MACO scheme possesses the potential to serve as a generic platform for identifying synergistic antimicrobial cocktails toward management of bacterial infection in the future.

Review of antimicrobial and antioxidative activities of chitosans in food

Interest in chitosan, a biodegradable, nontoxic, non-antigenic, and biocompatible biopolymer isolated from shellfish, arises from the fact that chitosans are reported to exhibit numerous health-related beneficial effects, including strong antimicrobial and antioxidative activities in foods. The extraordinary interest in the chemistry and application in agriculture, horticulture, environmental science, industry, microbiology, and medicine is attested by about 17,000 citations on this subject in the Scopus database. A special need exists to develop a better understanding of the role of chitosans in ameliorating foodborne illness. To contribute to this effort, this overview surveys and interprets our present knowledge of the chemistry and antimicrobial activities of chitosan in solution, as powders, and in edible films and coating against foodborne pathogens, spoilage bacteria, and pathogenic viruses and fungi in several food categories. These include produce, fruit juices, eggs and dairy, cereal, meat, and seafood products. Also covered are antimicrobial activities of chemically modified and nanochitosans, therapeutic properties, and possible mechanisms of the antimicrobial, antioxidative, and metal chelating effects. Further research is suggested in each of these categories. The widely scattered data on the multifaceted aspects of chitosan microbiology, summarized in the text and in 10 tables and 8 representative figures, suggest that low-molecular-weight chitosans at a pH below 6.0 presents optimal conditions for achieving desirable antimicrobial and antioxidative-preservative effects in liquid and solid foods. We are very hopeful that the described findings will be a valuable record and resource for further progress to improve microbial food safety and food quality.

Inhibition of biological activity of staphylococcal enterotoxin A (SEA) by apple juice and apple polyphenols

The foodborne pathogen Staphylococcus aureus produces the virulent staphylococcal enterotoxin A (SEA), a single-chain protein that consists of 233 amino acid residues with a molecular weight of 27 078 Da. SEA is a superantigen that is reported to contribute to animal (mastitis) and human (emesis, diarrhea, atopic dermatitis, arthritis, and toxic shock) syndromes. Changes of the native structural integrity may inactivate the toxin by preventing molecular interaction with cell membrane receptor sites of their host cells. In the present study, we evaluated the ability of one commercial and two freshly prepared apple juices and a commercial apple polyphenol preparation (Apple Poly) to inhibit the biological activity of SEA. Dilutions of freshly prepared apple juices and Apple Poly inhibited the biological activity of SEA without any significant cytotoxic effect on the spleen cells. Additional studies with antibody-coated immunomagnetic beads bearing specific antibodies against the toxin revealed that SEA added to apple juice appears to be largely irreversibly bound to the juice constituents. The results suggest that food-compatible and safe anti-toxin phenolic compounds can be used to inactivate SEA in vitro and possibly also in vivo, even after induction of T-cell proliferation by long-term exposure to SEA. The significance of the results for microbial food safety and human health is discussed.

Carvacrol and cinnamaldehyde inactivate antibiotic-resistant Salmonella enterica in buffer and on celery and oysters

The emergence of antibiotic-resistant Salmonella is of concern to food processors. The objective of this research was to identify antimicrobial activities of cinnamaldehyde and carvacrol against antibiotic-resistant Salmonella enterica in phosphate-buffered saline (PBS) and on celery and oysters. Twenty-three isolates were screened for resistance to seven antibiotics. Two resistant and two susceptible strains were chosen for the study. S. enterica cultures (10(5) CFU/ml) were added to different concentrations of cinnamaldehyde and carvacrol (0.1, 0.2, 0.3, and 0.4% [vol/vol]) in PBS, mixed, and incubated at 37 degrees C. Samples were taken at 0, 1, 5, and 24 h for enumeration. Celery and oysters were inoculated with S. enterica (10(6-7) CFU/ml), treated with 1% cinnamaldehyde or 1% carvacrol, incubated at 4 degrees C, and then sampled for enumeration on days 0 and 3. Both antimicrobials induced complete inactivation of S. enterica in PBS at 0.3 and 0.4% on exposure, and on 0.2% in 1 h. Exposure to cinnamaldehyde at 0.1% inactivated all pathogens at 1 h, and survivors were observed only for Salmonella Newport with 0.1% carvacrol at 1 h. In celery, 1% carvacrol reduced S. enterica populations to below detection on day 0, while 1% cinnamaldehyde reduced populations by 1 and 2.3 log on day 0 and day 3, respectively. In oysters, both antimicrobials caused about 5-log reductions on day 3. These results show the potential antimicrobial effects of carvacrol and cinnamaldehyde against antibiotic-resistant S. enterica in vitro and in foods.

Antibacterial activities of naturally occurring compounds against Mycobacterium avium subsp. paratuberculosis

The antibacterial activities of 18 naturally occurring compounds (including essential oils and some of their isolated constituents, apple and green tea polyphenols, and other plant extracts) against three strains of Mycobacterium avium subsp. paratuberculosis (a bovine isolate [NCTC 8578], a raw-milk isolate [806R], and a human isolate [ATCC 43015]) were evaluated using a macrobroth susceptibility testing method. M. avium subsp. paratuberculosis was grown in 4 ml Middlebrook 7H9 broth containing 10% oleic acid-albumin-dextrose-catalase, 0.05% Tween 80 (or 0.2% glycerol), and 2 microg/ml mycobactin J supplemented with five concentrations of each test compound. The changes in the optical densities of the cultures at 600 nm as a measure of CFU were recorded at intervals over an incubation period of 42 days at 37 degrees C. Six of the compounds were found to inhibit the growth of M. avium subsp. paratuberculosis. The most effective compound was trans-cinnamaldehyde, with a MIC of 25.9 microg/ml, followed by cinnamon oil (26.2 microg/ml), oregano oil (68.2 microg/ml), carvacrol (72.2 microg/ml), 2,5-dihydroxybenzaldehyde (74 microg/ml), and 2-hydroxy-5-methoxybenzaldehyde (90.4 microg/ml). With the exception of carvacrol, a phenolic compound, three of the four most active compounds are aldehydes, suggesting that the structure of the phenolic group or the aldehyde group may be important to the antibacterial activity. No difference in compound activity was observed between the three M. avium subsp. paratuberculosis strains studied. Possible mechanisms of the antimicrobial effects are discussed.

Carvacrol and cinnamaldehyde facilitate thermal destruction of Escherichia coli O157:H7 in raw ground beef

The heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of the antimicrobials carvacrol and cinnamaldehyde was tested at temperatures ranging from 55 to 62.5 degrees C. Inoculated meat packaged in bags was completely immersed in a circulating water bath, cooked for 1 h to an internal temperature of 55, 58, 60, or 62.5 degrees C, and then held for predetermined lengths of time ranging from 210 min at 55 degrees C to 5 min at 62.5 degrees C. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with sorbitol MacConkey agar. Inactivation kinetics of the pathogens deviated from first-order kinetics. D-values (time for the bacteria to decrease by 90%) in the control beef ranged from 63.90 min at 55 degrees C to 1.79 min at 62.5 degrees C. D-values determined by a logistic model ranged from 43.18 min (D1, the D-value of a major population of surviving cells) and 89.84 min (D2, the D-value of a minor subpopulation) at 55 degrees C to 1.77 (D1) and 0.78 min (D2) at 62.5 degrees C. The thermal death times suggested that to achieve a 4-D reduction, contaminated processed ground beef should be heated to an internal temperature of 60 degrees C for at least 30.32 min. Significantly increased sensitivity to heat (P < 0.05) was observed with the addition and/or increasing levels of carvacrol or cinnamaldehyde from 0.5 to 1.0%. The observed thermal death times may facilitate the design of acceptance limits at critical control points for ground beef at lower times and temperatures of heating.

Plant-derived compounds inactivate antibiotic-resistant Campylobacter jejuni strains

Sixty-three Campylobacter jejuni isolates were screened for their resistance to the antibiotics ampicillin, cefaclor, ciprofloxacin, erythromycin, gentamycin, tetracycline, and trimethoprim-sulfamethoxazole. Based on this screen, the resistant strains D28a and H2a and the nonresistant strain A24a were selected for evaluation of their resistance and susceptibility to inactivation by cinnamaldehyde and carvacrol, the main constituents of plant-derived cinnamon and oregano oils, respectively. Different concentrations (0.05, 0.1, and 0.2% [vol/vol] in sterile phosphate-buffered saline) of cinnamaldehyde and carvacrol were added to C. jejuni cultures with initial populations of 10(4) CFU/ml. The samples were then mixed thoroughly and incubated at 37 degrees C. Viable bacterial populations were enumerated at incubation periods of 0, 30, 60, and 120 min. The results indicate that the extent of inhibition of microbial survival was related to both the nature and concentration of antimicrobials and the incubation time. Both cinnamaldehyde and carvacrol exhibited rapid antimicrobial activity against both antibiotic-resistant and non-resistant C. jejuni strains, at concentrations of approximately 0.1% and higher. The antimicrobial efficacy of cinnamaldehyde was greater than that of carvacrol. The possible significance of the results for microbiological food safety is discussed.

Overview of antibacterial, antitoxin, antiviral, and antifungal activities of tea flavonoids and teas

Tea leaves produce organic compounds that may be involved in the defense of the plants against invading pathogens including insects, bacteria, fungi, and viruses. These metabolites include polyphenolic compounds, the six so-called catechins, and the methyl-xanthine alkaloids caffeine, theobromine, and theophylline. Postharvest inactivation of phenol oxidases in green tea leaves prevents oxidation of the catechins, whereas postharvest enzyme-catalyzed oxidation (fermentation) of catechins in tea leaves results in the formation of four theaflavins as well as polymeric thearubigins. These substances impart the black color to black teas. Black and partly fermented oolong teas contain both classes of phenolic compounds. A need exists to develop a better understanding of the roles of polyphenolic tea compounds in food and medical microbiology. This overview surveys and interprets our present knowledge of activities of tea flavonoids and teas against foodborne and other pathogenic bacteria, virulent protein toxins produced by some of the bacteria, virulent bacteriophages, pathogenic viruses and fungi. Also covered are synergistic, mechanistic, and bioavailability aspects of the antimicrobial effects. Further research is suggested for each of these categories. The herein described findings are not only of fundamental interest, but also have practical implications for nutrition, food safety, and animal and human health.