Antibiofilm effect of plant derived antimicrobials on Listeria monocytogenes

Antibiofilm Efficacy and Mechanism of the Marine Chlorinated Indole Sesquiterpene Against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) can easily form biofilms on food surfaces, thus leading to cross-contamination, which is difficult to remove. Therefore, there is an urgent need to find alternatives with good antibacterial and antibiofilm effects. In this study, two indole sesquiterpene compounds, xiamycin (1) and chlorinated metabolite chloroxiamycin (2), were isolated from the fermentation liquid of marine Streptomyces sp. NBU3429 for the first time. The chemical structures of the two compounds were characterized by spectroscopic data interpretation, including 1D NMR and HRESIMS analysis. Antimicrobial test showed that chloroxiamycin (2) (minimum inhibitory concentration, MIC = 16 μg/mL) exhibited superior antibacterial activity than xiamycin (1) (MIC = 32 μg/mL) against MRSA ATCC43300. Moreover, compound (2) decreased the biofilm formation rate of MRSA ATCC43300 by 12.7%-84.6% in the concentration range of 32-512 μg/mL, which is relatively stronger than xiamycin (1) (4.1%-49.9%) as well. Antibacterial/antibiofilm mechanism investigation indicated that chloroxiamycin (2) could disrupt the cell wall and membrane of MRSA, inhibiting the production of biofilm extracellular polysaccharides. All these results illustrated that chloroxiamycin (2) is an effective antibacterial/antibiofilm agent, which makes it an attractive candidate for food preservatives.

New insights into the antibiofilm activity and mechanism of Mannosylerythritol Lipid-A against Listeria monocytogenes EGD-e

Listeria monocytogenes is one of the leading causative agents of foodborne disease outbreaks worldwide. Herein, the antibiofilm effect and mechanism of Mannosylerythritol Lipid-A against L. monocytogenes EGD-e is reported for the first time. MEL-A effectively attenuated biofilm formation while reducing the viability and motility of bacteria within the biofilm in the early stage, and influenced bacterial adhesion by affecting the secretion of extracellular polysaccharides and eDNA. RT-qPCR revealed that MEL-A significantly suppressed the expression of genes involved in flagellar movement and virulence. Untargeted LC-MS metabolomics indicated that MEL-A affected the fluidity and permeability of cell membranes by significantly upregulating unsaturated fatty acids, lipids and glycoside metabolites, and affected protein biosynthesis, nucleotide metabolism and DNA synthesis and repair by significantly downregulating amino acid metabolism and nucleic acid metabolism. These pathways may constitute the key targets of biofilm formation inhibition by MEL-A. Furthermore, MEL-A showed good removal effects on mature biofilms under different temperatures, different materials and milk. Our data indicated that MEL-A could be used as a novel antibiofilm agent to improve food safety. Our study provides new insights into the possible inhibitory mechanism of MEL-A and the response of L. monocytogenes EGD-e to MEL-A.

Oleanolic Acid Promotes the Formation of Probiotic Escherichia coli Nissle 1917 (EcN) Biofilm by Inhibiting Bacterial Motility

Probiotic biofilms have been beneficial in the fight against infections, restoring the equilibrium of the host's gut microbiota, and enhancing host health. They are considered a novel strategy for probiotic gut colonization. In this case, we evaluated the effects of various active substances from traditional Chinese medicine on Escherichia coli Nissle 1917 (EcN) to determine if they promote biofilm formation. It was shown that 8-64 μg/mL of oleanolic acid increased the development of EcN biofilm. Additionally, we observed that oleanolic acid can effectively suppress biofilm formation in pathogenic bacteria such as Salmonella and Staphylococcus aureus. Next, we assessed the amount of EcN extracellular polysaccharides, the number of live bacteria, their metabolic activity, the hydrophobicity of their surface, and the shape of their biofilms using laser confocal microscopy. Through transcriptome analysis, a total of 349 differentially expressed genes were identified, comprising 134 upregulated and 215 downregulated genes. GO functional enrichment analysis and KEGG pathway enrichment analysis revealed that oleanolic acid functions are through the regulation of bacterial motility, the iron absorption system, the two-component system, and adhesion pathways. These findings suggest that the main effects of oleanolic acid are to prevent bacterial motility, increase initial adhesion, and encourage the development of EcN biofilms. In addition, oleanolic acid interacts with iron absorption to cooperatively control the production of EcN biofilms within an optimal concentration range. Taking these results together, this study suggests that oleanolic acid may enhance probiotic biofilm formation in the intestines, presenting new avenues for probiotic product development.

Plant-derived bioactive compounds for the inhibition of biofilm formation: a comprehensive review

Biofilm formation is a widespread phenomenon that impacts different fields, including the food industry, agriculture, health care and the environment. Accordingly, there is a serious need for new methods of managing the problem of biofilm formation. Natural products have historically been a rich source of varied compounds with a wide variety of biological functions, including antibiofilm agents. In this review, we critically highlight and discuss the recent progress in understanding the antibiofilm effects of several bioactive compounds isolated from different plants, and in elucidating the underlying mechanisms of action and the factors influencing their adhesion. The literature shows that bioactive compounds have promising antibiofilm potential against both Gram-negative and Gram-positive bacterial and fungal strains, via several mechanisms of action, such as suppressing the formation of the polymer matrix, limiting O2 consumption, inhibiting microbial DNA replication, decreasing hydrophobicity of cell surfaces and blocking the quorum sensing network. This antibiofilm activity is influenced by several environmental factors, such as nutritional cues, pH values, O2 availability and temperature. This review demonstrates that several bioactive compounds could mitigate the problem of biofilm production. However, toxicological assessment and pharmacokinetic investigations of these molecules are strongly required to validate their safety.

Design of a Novel Lysine Isopeptide 1018KI11 with Potent Antimicrobial Activity as a Safe and Stable Food Preservative Candidate

Antimicrobial peptides are potent food additive candidates, but most of them are sensitive to proteases, which limits their application. Therefore, we substituted arginine for lysine and introduced a lysine isopeptide bond to peptide IDR-1018 in order to improve its enzymatic stability. Subsequently, the protease stability and antimicrobial/antibiofilm activity of the novel peptides (1018K2-1018KI11) were investigated. The data revealed that the antienzymatic potential of 1018KI11 to bromelain and papain increased by 2-8 folds and 16 folds, respectively. The minimum inhibitory concentration (MIC) of 1018KI11 against methicillin-resistant Staphylococcus aureus (MRSA) ATCC43300 and Escherichia coli (E. coli) ATCC25922 was reduced 2-fold compared to 1018K11. Mechanism exploration suggested that 1018KI11 was more effective than 1018K11 in disrupting the cell barrier and damaging genomic DNA. Additionally, 1018KI11 at certain concentration conditions (2-64 μg/mL) reduced biofilm development of MRSA ATCC43300 by 4.9-85.9%. These data indicated that novel peptide 1018KI11 is a potential food preservative candidate.

Insights into the preventive actions of natural compounds against Klebsiella pneumoniae infections and drug resistance

Klebsiella pneumoniae is a type of Gram-negative bacteria that causes a variety of infections, including pneumonia, bloodstream infections, wound infections, and meningitis. The treatment of K. pneumoniae infection depends on the type of infection and the severity of the symptoms. Antibiotics are generally used to treat K. pneumoniae infections. However, some strains of K. pneumoniae have become resistant to antibiotics. This comprehensive review examines the potential of natural compounds as effective strategies against K. pneumonia infections. The alarming rise in antibiotic resistance underscores the urgent need for alternative therapies. This article represents current research on the effects of diverse natural compounds, highlighting their anti-microbial and antibiofilm properties against K. pneumonia. Notably, compounds such as andrographolide, artemisinin, baicalin, berberine, curcumin, epigallocatechin gallate, eugenol, mangiferin, piperine, quercetin, resveratrol, and thymol have been extensively investigated. These compounds exhibit multifaceted mechanisms, including disruption of bacterial biofilms, interference with virulence factors, and augmentation of antibiotic effectiveness. Mechanistic insights into their actions include membrane perturbation, oxidative stress induction, and altered gene expression. While promising, challenges such as limited bioavailability and varied efficacy across bacterial strains are addressed. This review further discusses the potential of natural compounds as better alternatives in combating K. pneumonia infection and emphasizes the need for continued research to harness their full therapeutic potential. As antibiotic resistance persists, these natural compounds offer a promising avenue in the fight against K. pneumonia and other multidrug-resistant pathogens.

Effect of pimenta essential oil against Salmonella Agona and Salmonella Saintpaul in ground turkey meat and nonprocessed turkey breast meat

Salmonella enterica Agona (S. Agona) and Salmonella enterica Saintpaul (S. Saintpaul) are among the emerging drug-resistant Salmonella in turkey production and processing. Rapid solutions to control emerging and uncommon serotypes such as S. Agona and S. Saintpaul are needed. This study tested pimenta essential oil (PEO) as a processing antibacterial against S. Agona and S. Saintpaul in experiments representative of different stages of turkey processing. The compound effectively reduced S. Agona and S. Saintpaul in nutrient broth studies and with mature biofilm assays. PEO was tested against a combination of S. Agona and S. Saintpaul in ground turkey meat and nonprocessed breast meat. In the first experiment with ground turkey, samples were inoculated with a mixture of S. Agona and S. Saintpaul (∼3 log10 CFU/g) and treated with PEO at different concentrations (0% PEO, 0.25% PEO, 0.5% PEO, 1% PEO, 2% PEO, and 2.5% PEO). In the second experiment with turkey breast, samples inoculated with ∼3 log10 CFU/g (SA+SP) were dipped in different concentrations of PEO with chitosan (CN) for 2 min. In both these experiments, samples were stored at 4°C, and Salmonella recovery was carried out at 0, 1, 3, 5, and 7 d. All experiments followed a completely randomized design and were repeated 6 times (n = 6). Statistical analysis was done using the PROC-ANOVA procedure of SAS. In the ground turkey meat, PEO at or above 2% reduced 2 log10 CFU/g of Salmonella by day 1. PEO at 2.5% in ground turkey meat resulted in enrichment-negative samples by 1 min, indicative of the rapid killing effect of the compound at a high concentration of PEO (P ≤ 0.05). A maximum reduction of 1.7 log10 CFU Salmonella/g of turkey breast meat was obtained after 2 min of dip treatment containing CN and 2.5% PEO. Results indicate that PEO could be used as a plant-based processing antibacterial against S. Agona and S. Saintpaul in turkey processing. Upscaling to plant-level studies is necessary before recommending its usage.

Effects of Sub-Minimum Inhibitory Concentrations of Bacteriocin BM173 on Listeria Monocytogenes Biofilm Formation

Listeria monocytogenes is a significant foodborne pathogen that can form biofilms on various food processing surfaces, thereby enhancing resistance to disinfectants and exacerbating harm to human health. Previous studies have indicated that bacteriocin BM173 exhibits antibacterial and antibiofilm activities. In the current study, our aim was to assess the inhibitory mode of action of sub-inhibitory concentrations (SICs, 1/32 × MIC and 1/16 × MIC) of BM173 on the biofilm formation L. monocytogenes. Crystal violet staining assay revealed that SICs of BM173 significantly inhibit L. monocytogenes biofilm formation. Furthermore, the results of swimming motility assay, plate count, ruthenium red staining, and scanning electron microscopy (SEM) revealed that SICs of BM173 could effectively reduce the movement, cell adhesion, and exopolysaccharide (EPS) production of L. monocytogenes, thereby inhibiting biofilm formation. Real-time quantitative PCR analyses further demonstrated that SICs of BM173 down-regulated the expression of biofilm-associated genes, including those encoding adhesion, virulence factors, and quorum sensing. Additionally, SICs of BM173 effectively reduced the biofilm formation of L. monocytogenes on the surfaces of three food-grade materials (glass, stainless steel, and silicone) at 4 and 25 °C. These outcomes suggest that BM173 holds great potential for development as a promising food preservative for application in the food industry.

Antibiofilm potential of luteolin against multidrug-resistant Staphylococcus aureus isolated from dairy goats and farm environments

Staphylococcus aureus (S. aureus) is a prominent pathogen responsible for mastitis in dairy goats, and capable of contaminating farm environments. Luteolin is a naturally derived flavonoid found in many plant types. To our best of knowledge, this study involved the initial investigation into the prevalence of S. aureus and screened the multidrug-resistant (MDR) S. aureus from raw milk samples and farm environments. Furthermore, we explored the antimicrobial and antibiofilm activities of luteolin against MDR S. aureus. Antibiofilm activity was evaluated via crystal violet staining and confocal laser scanning microscopy (CLSM). Bacterial morphology and biofilm microstructure were observed via scanning electron microscopy (SEM), and the antibiofilm mechanisms were further explored based on extracellular polymeric substance (EPS) production, extracellular DNA (eDNA) content, and quantitative reverse transcription PCR (qRT-PCR). In total, 28 and 43 S. aureus isolates were isolated from raw milk and environmental samples, respectively. Raw milk samples had the highest prevalence of S. aureus (58.33%), followed by sewage sludge (35.42%), soil (27.78%), excrement (19.44%), bulk tank (12.50%), milking parlor (11.11%), and feed (7.50%). Among the isolated strains, 40 isolates (56.34%) expressed the MDR phenotype. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of luteolin against MDR S. aureus were 8-32 μg/mL and 16-64 μg/mL, respectively. Compared to that in the untreated control isolate, the number of dead cells increased, while the auto-aggregation and cell surface hydrophobicity decreased. Moreover, the cell membrane dissolved with the increase in luteolin concentration. Luteolin down-regulated the transcription of seven biofilm related genes: icaA, icaD, icab, hld, hla, agrA and RNAIII. These results indicated that S. aureus coexisted in raw milk and goat farm environments, and also suggested the potential of luteolin as a promising antibiofilm agent against MDR S. aureus.

Influences of flavonoids from Sedum aizoon L. on biofilm formation of Pseudomonas fragi

Pseudomonas fragi (P. fragi) is one of the main categories of bacteria responsible for the spoilage of chilled meat. In the processing and preservation of chilled meat, it is easy to form biofilms on the meat, leading to the development of slime on the meat, which becomes a major quality defect. Flavonoids, as one of the critical components of secondary plant metabolites, are receiving increasing attention for their antibacterial activity. Flavonoids in Sedum aizoon L. (FSAL), relying on its prominent antibacterial activity, are of research importance in food preservation and other applications. This article aims to investigate the effect of FSAL on the biofilm formation of P. fragi, to better apply FSAL to the processing and preservation of meat products. The disruption of cellular structure and aggregation properties by FSAL was demonstrated by the observation of the cellular state within the biofilm. The amount of biofilm formation was determined by crystal violet staining, and the content of polysaccharides and proteins in the extracellular wrapped material was determined. It was shown that the experimental concentrations of FSAL (1.0 MIC) was able to inhibit biofilm formation and reduce the main components in the extracellular secretion. The swimming motility assay and the downregulation of flagellin-related genes confirmed that FSAL reduced cell motility and adhesion. The downregulation of cell division genes and the lowering of bacterial metabolic activity suggested that FSAL could hinder bacterial growth and reproduction within P. fragi biofilms. KEY POINTS: • FSAL inhibited the activity of Pseudomonas fragi in the dominant meat strain • The absence of EPS components affected the formation of P. fragi biofilms • P. fragi has reduced adhesion capacity due to impaired flagellin function.

Correlation between Perturbation of Redox Homeostasis and Antibiofilm Capacity of Phytochemicals at Non-Lethal Concentrations

Biofilms are the multicellular lifestyle of microorganisms and are present on potentially every type of biotic or abiotic surface. Detrimental biofilms are generally targeted with antimicrobial compounds. Phytochemicals at sub-lethal concentrations seem to be an exciting alternative strategy to control biofilms, as they are less likely to impose selective pressure leading to resistance. This overview gathers the literature on individual phytocompounds rather than on extracts of which the use is difficult to reproduce. To the best of our knowledge, this is the first review to target only individual phytochemicals below inhibitory concentrations against biofilm formation. We explored whether there is an overall mechanism that can explain the effects of individual phytochemicals at sub-lethal concentrations. Interestingly, in all experiments reported here in which oxidative stress was investigated, a modest increase in intracellular reactive oxygen species was reported in treated cells compared to untreated specimens. At sub-lethal concentrations, polyphenolic substances likely act as pro-oxidants by disturbing the healthy redox cycle and causing an accumulation of reactive oxygen species.

Antibiofilm Effects of Bacteriocin BMP32r on Listeria monocytogenes

Listeria monocytogenes is a well-known foodborne pathogen that usually lives as biofilm to cope with unfavorable surroundings. Bacteriocins have been reported as antimicrobial compounds, and their bactericidal actions have been extensively studied, but their antibiofilm actions have rarely been studied. Previous study indicated that bacteriocin BMP32r has a broad-spectrum antibacterial activity. In this study, the efficacy of BMP32r against the planktonic bacteria, inhibition of forming biofilm, destruction of mature biofilm, and kill persisters of L. monocytogenes ATCC 15,313 was determined. BMP32r exhibited the bactericidal effect on L. monocytogenes planktonic bacteria. Crystal violet staining showed that sub-minimum inhibitory concentrations (SICs) of BMP32r (1/32 × MIC and 1/16 × MIC) significantly (p < 0.001) inhibit the biofilm formation. In addition, the results of CCK-8, plate count, ruthenium red staining, scanning electron microscopy, and real-time quantitative PCR assay showed that SICs of BMP32r reduced cell adhesion, exopolysaccharide production, quorum sensing, and virulence genes expression in biofilm formation. Moreover, higher concentrations of BMP32r (2 × MIC and 4 × MIC) disrupt the mature biofilm by killing the bacteria in the biofilm and kill L. monocytogenes persisters bacteria effectively. Therefore, BMP32r has promising potential as an antibiofilm agent to combat L. monocytogenes.

Potential of Aromatic Plant-Derived Essential Oils for the Control of Foodborne Bacteria and Antibiotic Resistance in Animal Production: A Review

Antibiotic resistance has become a severe public threat to human health worldwide. Supplementing antibiotic growth promoters (AGPs) at subtherapeutic levels has been a commonly applied method to improve the production performance of livestock and poultry, but the misuse of antibiotics in animal production plays a major role in the antibiotic resistance crisis and foodborne disease outbreaks. The addition of AGPs to improve production performance in livestock and poultry has been prohibited in some countries, including Europe, the United States and China. Moreover, cross-resistance could result in the development of multidrug resistant bacteria and limit therapeutic options for human and animal health. Therefore, finding alternatives to antibiotics to maintain the efficiency of livestock production and reduce the risk of foodborne disease outbreaks is beneficial to human health and the sustainable development of animal husbandry. Essential oils (EOs) and their individual compounds derived from aromatic plants are becoming increasingly popular as potential antibiotic alternatives for animal production based on their antibacterial properties. This paper reviews recent studies in the application of EOs in animal production for the control of foodborne pathogens, summarizes their molecular modes of action to increase the susceptibility of antibiotic-resistant bacteria, and provides a promising role for the application of nanoencapsulated EOs in animal production to control bacteria and overcome antibiotic resistance.

Eugenol nanoemulsion inactivates Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 on cantaloupes without affecting rind color

Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 are the major foodborne pathogens that have been implicated in outbreaks related to consumption of contaminated cantaloupes. Current chlorine-based decontamination strategies are not completely effective for inactivating the aforementioned pathogens on cantaloupes, especially in the presence of organic matter. This study investigated the efficacy of eugenol nanoemulsion (EGNE) wash treatments in inactivating L. monocytogenes, Salmonella spp., and E. coli O157:H7 on the surface of cantaloupes. In addition, the efficacy of EGNE in inhibiting the growth of the three pathogens on cantaloupes during refrigerated and room temperature storage of 5 days was investigated. Moreover, the effect of EGNE wash treatment on cantaloupe color was assessed using a Miniscan® XE Plus. The EGNE was prepared with either Tween 80 (TW) or a combination of Gum arabic and Lecithin (GA) as emulsifiers. The cantaloupe rind was washed with EGNE (0.3, 0.6, and 1.25%), in presence or absence of 5% organic load, for 1, 5, or 10 min at 25°C. Enumeration of surviving pathogens on cantaloupe was performed by serial dilution and plating on Oxford, XLD or SMA agar followed by incubation at 37°C for 24–48 h. EGNE-GA and EGNE-TW wash significantly reduced all three pathogens by at least 3.5 log CFU/cm2 as early as 5 min after treatment. EGNE-GA at 1.25% inactivated L. monocytogenes, E. coli O157:H7 and S. Enteritidis on cantaloupes to below the detectable limit within 5 and 10 min of treatment, respectively (~4 log CFU/cm2, P &lt; 0.05). EGNE treatments significantly reduced the survival of L. monocytogenes, S. Enteritidis, and E. coli O157:H7 on cantaloupe by at least 6 log CFU/cm2 at day 5 of storage at 25 and 4°C (P &lt; 0.05). Presence of organic matter did not modulate the antimicrobial efficacy of nanoemulsion treatments (P &gt; 0.05). EGNE treatments did not affect the rind color of cantaloupes (P &gt; 0.05). In conclusion, eugenol nanoemulsions could potentially be used as a natural sanitizer to inactivate foodborne pathogens on cantaloupes. Further investigations in an industry setting are warranted.

Impact of Sub-MIC Eugenol on Klebsiella pneumoniae Biofilm Formation via Upregulation of rcsB

The Rcs phosphorelay system is present in many members of the Enterobacteriaceae. The aim of this study was to illustrate the possible mechanisms of eugenol on ultimate targets of Klebsiella pneumoniae (K. pneumoniae) Rcs phosphorelay, rcsB, and impact on biofilm formation. The minimum inhibitory concentration (MIC) of eugenol against K. pneumoniae KP1 and KP1 ΔrcsB strain was determined using the 2-fold micro-dilution method. Biofilm was measured by crystal violet staining. Transcriptome sequencing was performed to investigate sub-MIC eugenol on K. pneumoniae, and gene expression at mRNA level was analyzed by RT-qPCR. In vitro biofilm formation test and molecular docking were used to evaluate the effect of eugenol and to predict potential interactions with RcsB. MicroScale Thermophoresis (MST) was conducted for further validation. MIC of eugenol against K. pneumoniae KP1 and KP1 ΔrcsB strain was both 200 μg/ml. Transcriptome sequencing and RT-qPCR results indicated that rpmg, degP, rnpA, and dapD were downregulated, while rcsB, rcsD, rcsA, yiaG, and yiaD were upregulated in the eugenol-treated group. ΔrcsB exhibited a weakened biofilm formation capacity. Additional isopropyl-β-d-thiogalactoside (IPTG) hinders biofilm formation, while sub-MIC eugenol could promote biofilm formation greatly. Docking analysis revealed that eugenol forms more hydrophobic bonds than hydrogen bonds. MST assay also showed a weak binding affinity between eugenol and RcsB. These results provide significant evidence that rcsB plays a key role in K. pneumoniae biofilm formation. Sub-MIC eugenol facilitates biofilm formation to a large extent instead of inhibiting it. Our findings reveal the potential risk of natural anti-biofilm ingredients at sub-MIC to treat drug-resistance bacteria.

Cinnamomum: The New Therapeutic Agents for Inhibition of Bacterial and Fungal Biofilm-Associated Infection

Due to the potent antibacterial properties of Cinnamomum and its derivatives, particularly cinnamaldehyde, recent studies have used these compounds to inhibit the growth of the most prevalent bacterial and fungal biofilms. By inhibiting flagella protein synthesis and swarming motility, Cinnamomum could suppress bacterial attachment, colonization, and biofilm formation in an early stage. Furthermore, by downregulation of Cyclic di‐guanosine monophosphate (c‐di‐GMP), biofilm-related genes, and quorum sensing, this compound suppresses intercellular adherence and accumulation of bacterial cells in biofilm and inhibits important bacterial virulence factors. In addition, Cinnamomum could lead to preformed biofilm elimination by enhancing membrane permeability and the disruption of membrane integrity. Moreover, this substance suppresses the Candida species adherence to the oral epithelial cells, leading to the cell wall deformities, damage, and leakages of intracellular material that may contribute to the established Candida’s biofilm elimination. Therefore, by inhibiting biofilm maturation and destroying the external structure of biofilm, Cinnamomum could boost antibiotic treatment success in combination therapy. However, Cinnamomum has several disadvantages, such as poor solubility in aqueous solution, instability, and volatility; thus, the use of different drug-delivery systems may resolve these limitations and should be further considered in future investigations. Overall, Cinnamomum could be a promising agent for inhibiting microbial biofilm-associated infection and could be used as a catheter and other medical materials surface coatings to suppress biofilm formation. Nonetheless, further in vitro toxicology analysis and animal experiments are required to confirm the reported molecular antibiofilm effect of Cinnamomum and its derivative components against microbial biofilm.

Biosynthesized Silver Nanoparticles from Eruca sativa Miller Leaf Extract Exhibits Antibacterial, Antioxidant, Anti-Quorum-Sensing, Antibiofilm, and Anti-Metastatic Activities

Worldwide, the primary problem today is the proliferation of cancer and secondary bacterial infections caused by biofilms, as they are the principal causes of death due to the lack of effective drugs. A great deal of biological activities of silver nanoparticles (AgNPs) have made them a brilliant choice for the development of new drugs in recent years. The present study was conducted to evaluate the anticancer, antibacterial, anti-QS, and antibiofilm effects of AgNPs synthesized from Eruca sativa (E. sativa) leaf extract. The ultraviolet–visible (UV–Vis) spectra showed a peak of surface plasmon resonance at 424 nm λmax, which corresponded to AgNP formation. The Fourier transform infrared spectroscopy (FT-IR) confirmed that biological moieties are involved for the development of AgNPs. Moreover, transmission electron microscopy (TEM) analyses confirmed the spherical shape and uniform size (8.11 to 15 nm) of the AgNPs. In human lung cancer cells (A549), the anticancer potential of AgNPs was examined by the MTT [3-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, scratch assay, and invasion assay. The results indicated that AgNPs inhibit the migration of A549 cells. The synthesized AgNPs showed MIC values of 12.5 µg/mL against Chromobacterium violaceum (C. violaceum) and 25 µg/mL against Pseudomonas aeruginosa (P. aeruginosa), which demonstrated their antibacterial abilities. Biological compounds that disable the QS system are being investigated as potential strategies for preventing bacterial infections. Thus, we analyzed the potential effectiveness of synthesized AgNPs in inhibiting QS-regulated virulence factors and biofilm formation in both strains of bacteria. In C. violaceum, the synthesized AgNPs significantly inhibited both violacein (85.18% at 1/2 × MIC) and acyl homoserine lactone (78.76% at 1/2 × MIC). QS inhibitory activity was also demonstrated in P. aeruginosa at a sub-MIC concentration (1/2 × MIC) by a reduction in pyocyanin activity (68.83%), total protease (68.50%), LasA activity (63.91%), and LasB activity (56.40%). Additionally, the exopolysaccharide production was significantly reduced in both C. violaceum (65.79% at 1/2 × MIC) and P. aeruginosa (57.65% at 1/2 × MIC). The formation of biofilm was also significantly inhibited at 1/2 × MIC in C. violaceum (76.49%) and in P. aeruginosa (65.31%). Moreover, a GC–MS analysis confirmed the presence of different classes of bioactive phytochemical constituents present in the leaf extract of E. sativa. On the basis of our results, we conclude that biologically synthesized AgNPs showed numerous multifunctional properties and have the potential to be used against human cancer and bacterial biofilm-related infections.

Lactiplantibacillus plantarum-Derived Biosurfactant Attenuates Quorum Sensing-Mediated Virulence and Biofilm Formation in Pseudomonas aeruginosa and Chromobacterium violaceum

Quorum sensing (QS) controls the expression of diverse biological traits in bacteria, including virulence factors. Any natural bioactive compound that disables the QS system is being considered as a potential strategy to prevent bacterial infection. Various biological activities of biosurfactants have been observed, including anti-QS effects. In the present study, we investigated the effectiveness of a biosurfactant derived from Lactiplantibacillus plantarum on QS-regulated virulence factors and biofilm formation in Pseudomonas aeruginosa and Chromobacterium violaceum. The structural analogues of the crude biosurfactant were identified using gas chromatography–mass spectrometry (GC–MS). Moreover, the inhibitory prospects of identified structural analogues were assessed with QS-associated CviR, LasA, and LasI ligands via in silico molecular docking analysis. An L. plantarum-derived biosurfactant showed a promising dose-dependent interference with the production of both violacein and acyl homoserine lactone (AHL) in C. violaceum. In P. aeruginosa, at a sub-MIC concentration (2.5 mg/mL), QS inhibitory activity was also demonstrated by reduction in pyocyanin (66.63%), total protease (60.95%), LasA (56.62%), and LasB elastase (51.33%) activity. The swarming motility and exopolysaccharide production were also significantly reduced in both C. violaceum (61.13%) and P. aeruginosa (53.11%). When compared with control, biofilm formation was also considerably reduced in C. violaceum (68.12%) and P. aeruginosa (59.80%). A GC–MS analysis confirmed that the crude biosurfactant derived from L. plantarum was a glycolipid type. Among all, n-hexadecanoic acid, oleic acid, and 1H-indene,1-hexadecyl-2,3-dihydro had a high affinity for CviR, LasI, and LasA, respectively. Thus, our findings suggest that the crude biosurfactant of L. plantarum can be used as a new anti-QS/antibiofilm agent against biofilm-associated pathogenesis, which warrants further investigation to uncover its therapeutic efficacy.

The combination of thymol and cinnamaldehyde reduces the survival and virulence of Listeria monocytogenes on autoclaved chicken breast

AIMS

To reveal the antibacterial mechanism of the combination of thymol and cinnamaldehyde to Listeria monocytogenes ATCC 19115 on autoclaved chicken breast.

METHODS AND RESULTS

In this study, Listeria monocytogenes ATCC 19115 on autoclaved chicken breast was exposed to the stress of 125 μg/mL thymol and 125 μg/mL cinnamaldehyde, and transcriptome analysis was used to reveal the crucial antibacterial mechanism. According to the results, 1303 significantly differentially expressed genes (DEGs) were identified. Treated by thymol and cinnamaldehyde in combination, pyrimidine and branched-chain amino acids biosynthesis of L. monocytogenes were thwarted which impairs its nucleic acid biosynthesis and intracellular metabolism. The up-regulated DEGs involved in membrane composition and function contributed to membrane repair. Besides, pyruvate catabolism and TCA cycle were restrained which brought about the disturbance of amino acid metabolism. ABC transporters were also perturbed, for instance, the uptake of cysteine, D-methionine and betaine was activated, while the uptake of vitamin, iron and carnitine was repressed. Thus, L. monocytogenes tended to activate PTS, glycolysis, glycerol catabolism, and pentose phosphate pathways to obtain energy to adapt to the hostile condition. Noticeably, DEGs involved in virulence factors were totally down-regulated, including genes devoted to encoding flagella, chemotaxis, biofilm formation, internalin as well as virulence gene clusters.

CONCLUSIONS

The combination of thymol and cinnamaldehyde is effective to reduce the survival and potential virulence of L. monocytogenes on autoclaved chicken breast.

SIGNIFICANCE AND IMPACT OF STUDY

This work contributes to providing theoretical information for the application and optimization of thymol and cinnamaldehyde in ready-to-eat meat products to inhibit L. monocytogenes.

Campylobacter Biofilms: Potential of Natural Compounds to Disrupt Campylobacter jejuni Transmission

Microbial biofilms occur naturally in many environmental niches and can be a significant reservoir of infectious microbes in zoonotically transmitted diseases such as that caused by Campylobacter jejuni, the leading cause of acute human bacterial gastroenteritis world-wide. The greatest challenge in reducing the disease caused by this organism is reducing transmission of C. jejuni to humans from poultry via the food chain. Biofilms enhance the stress tolerance and antimicrobial resistance of the microorganisms they harbor and are considered to play a crucial role for Campylobacter spp. survival and transmission to humans. Unconventional approaches to control biofilms and to improve the efficacy of currently used antibiotics are urgently needed. This review summarizes the use plant- and microorganism-derived antimicrobial and antibiofilm compounds such as essential oils, antimicrobial peptides (AMPs), polyphenolic extracts, algae extracts, probiotic-derived factors, d-amino acids (DAs) and glycolipid biosurfactants with potential to control biofilms formed by Campylobacter, and the suggested mechanisms of their action. Further investigation and use of such natural compounds could improve preventative and remedial strategies aimed to limit the transmission of campylobacters and other human pathogens via the food chain.

Antimicrobial properties of Cnestis ferruginea Vahl ex DC

Scientific research into developing new antimicrobials from plants continues to be an interesting area for many scientists. This is because the resistance of microorganisms to anti-infective agents has affected a wide range of conditions, some of which are life-threatening. This study aimed to investigate the antimicrobial properties of Cnestis ferruginea (CF). Powdered roots of Cnestis ferruginea were extracted with petroleum ether (CFP), ethyl acetate (CFE) and methanol (CFM). The antimicrobial and microbial resistance modifying activity profiles of the extracts were studied against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 4853, Staphylococcus aureus ATCC 25923, clinical strains of Methicillin-Resistant Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumonia, Staphylococcus epidermidis, Proteus mirabilis and Candida albicans. CFP and CFE showed no activity against the test organisms. CFM had mean zones of growth inhibition in the range of 11.0 ± 0.5 to 22.17 ± 0.24 mm against the test organisms. The MIC of CFM was within the range of 0.31 and 5.0 mg/mL, with MBC/MFC range of 2.5-20.0 mg/mL. The time-kill kinetics studies showed CFM is a static agent. At sub-inhibitory concentrations, CFM was able to increase the susceptibility of the test organisms to standard antibiotics from the range of 1-8 folds. CFM reduced the formation of biofilms from 100% to 56.59%, 62.33%, 65.89% and 71.88% against K. pneumonia, S. aureus, E. coli and P. aeruginosa, respectively. The findings of this study show that C. ferruginea possesses antimicrobial activity and therefore gives credence to its folkloric use.

Volatile phenolics: A comprehensive review of the anti-infective properties of an important class of essential oil constituents

Historically, essential oils and their lead molecules have been extensively recognised for their anti-infective properties. In this context, certain volatile phenolics (VPs) have emerged as important antimicrobial compounds with excellent inhibitory activity against pathogenic bacteria and fungi, which further extends to drug-resistant and biofilm-forming micro-organisms. In this review, we aim to collate and discuss a number of published papers on the anti-infective activities of naturally occurring VPs with special emphasis on eugenol, isoeugenol, thymol and carvacrol, using Scopus Web of Science and PubMed databases. The biosynthesis and extraction of these VPs are discussed, while particular attention is given to their broad-spectrum antimicrobial activity and the mechanisms of action. We highlight combinational studies of the VPs with other phytocompounds and with commercially available drugs, which may be a promising and a rewarding future approach to combat antimicrobial resistance. These VPs alone, or concomitantly with other compounds or drugs, have the potential to be incorporated into different formulations for biomedical applications. An in-depth assessment of 2310 articles retrieved from the Scopus database spanning a 35-year period indicated 23.1% increase in global publication growth in VPs anti-infective research, with authors from Italy, Portugal and Austria dominating the research landscape. The dominant areas of investigations are identified as antimicrobial activity, antibacterial mechanism of action, antifungal mechanism of action, extraction methods and phytochemistry, use in the food industry, and for oral and dental anti-infective activity. Specific research areas, which require future attention include; antituberculosis research, nanoparticle formulation of antimicrobial active VP molecules, preclinical and clinical trials. The antimicrobial testing of isoeugenol was found to be the least studied of the VPs and this requires further attention.

Select Phytochemicals Reduce Campylobacter jejuni in Postharvest Poultry and Modulate the Virulence Attributes of C. jejuni

Consumption or handling of poultry and poultry products contaminated with Campylobacter species are a leading cause of foodborne illness in humans. Current strategies employed to reduce Campylobacter in live chickens provide inconsistent results indicating the need for an alternative approach. This study investigated the efficacy of phytochemicals, namely, turmeric, curcumin, allyl sulfide, garlic oil, and ginger oil, to reduce Campylobacter jejuni in postharvest poultry and sought to delineate the underlying mechanisms of action. Two experiments were conducted on the thigh skin of the chicken, and each experiment was repeated twice. Samples were inoculated with 50 μl (∼10⁷ CFU/sample) of C. jejuni strain S-8 and allowed to adhere for 30 min. Skin samples were dipped into their respective prechilled treatment solutions (0.25 and 0.5% in experiments 1 and 2, respectively) at 4°C for an hour to simulate chilling tank treatment, followed by plating to enumerate C. jejuni (n = 3 samples/treatment/trial). The mechanisms of action(s) were investigated using subinhibitory concentration (SIC) in adhesion, quorum sensing, and gene expression analyses. Adhesion assay was conducted on the monolayers of ATCC CRL-1590 chicken embryo cells challenged with C. jejuni and incubated in the presence or absence of phytochemicals for 1.5 h, followed by plating to enumerate adhered C. jejuni. The effects of phytochemicals on quorum sensing and cell viability were investigated using Vibrio harveyi bioluminescence and LIVE/Dead BacLight^TM bacterial viability assays, respectively. In addition, droplet digital PCR determined the gene expression analyses of C. jejuni exposed to phytochemicals. Data were analyzed by GraphPad Prism version 9. C. jejuni counts were reduced by 1.0–1.5 Log CFU/sample with garlic oil or ginger oil at 0.25 and 0.5% (p < 0.05). The selected phytochemicals (except curcumin) reduced the adhesion of C. jejuni to chicken embryo cells (p < 0.05). In addition, all the phytochemicals at SIC reduced quorum sensing of C. jejuni (p < 0.05). The cell viability test revealed that cells treated with 0.25% of phytochemicals had compromised cell membranes indicating this as a mechanism that phytochemicals use to damage/kill C. jejuni. This study supports that the application of phytochemicals in postharvest poultry would significantly reduce C. jejuni in poultry meat.

Strategies to combat antimicrobial resistance in Indian scenario

Antimicrobial resistance (AMR) is one of the major public health crisis recognised globally. Microbial infections cause significant productivity losses in animals and humans. In livestock, these microbial infections reduce the growth rates and fertility, diminish production of meat and milk, and occasionally lead to mortality, and are therefore, a major concern for animal welfare. In the dearth of alternative prophylactic measures, antibiotics remain the principal tool for their management. Once an antibiotic is used rampantly, resistance against it is inevidently seen in the microbe population and the hunt for a new drug grows. Discovery and development of a new antimicrobial drug is a time taking and expensive procedure with limited assurance of success. As a result, the past few decades have witnessed only a very few new classes of antibiotics. If the AMR can be restricted or reverted, the success rate of antimicrobial therapy can be boosted and many public health issues be avoided. All these ask for a comprehensive plan to prevent or reduce the antimicrobial resistance and economic losses to the animal husbandry sector. The present review provides an overview of AMR in India, mechanism of its occurrence and the possible roadmap to combat the emerging threat of AMR in Indian scenario.

Trans-Cinnamaldehyde Attenuates Enterococcus faecalis Virulence and Inhibits Biofilm Formation

Enterococcus faecalis as an important nosocomial pathogen is critically implicated in the pathogenesis of endocarditis, urinary tract, and persistent root canal infections. Its major virulence attributes (biofilm formation, production of proteases, and hemolytic toxins) enable it to cause extensive host tissue damage. With the alarming increase in enterococcal resistance to antibiotics, novel therapeutics are required to inhibit E. faecalis biofilm formation and virulence. Trans-cinnamaldehyde (TC), the main phytochemical in cinnamon essential oils, has demonstrated promising activity against a wide range of pathogens. Here, we comprehensively investigated the effect of TC on planktonic growth, biofilm formation, proteolytic and hemolytic activities, as well as gene regulation in E. faecalis. Our findings revealed that sub-inhibitory concentrations of TC reduced biofilm formation, biofilm exopolysaccharides, as well as its proteolytic and hemolytic activities. Mechanistic studies revealed significant downregulation of the quorum sensing fsr locus and downstream gelE, which are major virulence regulators in E. faecalis. Taken together, our study highlights the potential of TC to inhibit E. faecalis biofilm formation and its virulence.

Potential of Carvacrol and Thymol in Reducing Biofilm Formation on Technical Surfaces

Polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), and stainless steel (SS) are commonly used in medicine and food production technologies. During contact with microorganisms on the surface of these materials, a microbial biofilm is formed. The biofilm structure is difficult to remove and promotes the development of pathogenic bacteria. For this reason, the inhibition of biofilm formation in medical and food production environments is very important. For this purpose, five naturally occurring compounds were used for antimicrobial screening tests. The two with the best antimicrobial properties were chosen to inhibit the biofilm formation of Staphylococcus aureus and Pseudomonas aeruginosa. After 3 days of exposure, thymol reduced the amount of biofilm of Pseudomonas aeruginosa within the range of 70–77% and 52–75% for Staphylococcus aureus. Carvacrol inhibited the formation of biofilms by up to 74–88% for Pseudomonas aeruginosa and up to 86–100% for Staphylococcus aureus. Those phenols decreased the enzyme activity of the biofilm by up to 40–100%. After 10 days of exposure to thymol, biofilm formation was reduced by 80–100% for Pseudomonas aeruginosa and by about 79–100% for Staphylococcus aureus. Carvacrol reduced the amount of biofilm by up to 91–100% for Pseudomonas aeruginosa and up to 95–100% for Staphylococcus aureus.

Plant active products and emerging interventions in water potabilisation: disinfection and multi-drug resistant pathogen treatment

Background

This review aims at establishing the emerging applications of phytobiotics in water treatment and disinfection.

Results

Statistical analysis of data obtained revealed that the use of plant product in water treatment needs more research attention. A major observation is that plants possess multifaceted components and can be sustainably developed into products for water treatment. The seed (24.53%), flower (20.75), leaf (16.98%) and fruit (11.32%) biomasses are preferred against bulb (3.77%), resin (1.89%), bark (1.89%) and tuber (1.89%). The observation suggests that novel applications of plant in water treatment need further exploration since vast and broader antimicrobial activities (63.63%) is reported than water treatment application (36.37%).

Conclusions

This review has revealed the existing knowledge gaps in exploration of plant resources for water treatment and product development. Chemical complexity of some plant extracts, lack of standardisation, slow working rate, poor water solubility, extraction and purification complexities are limitations that need to be overcome for industrial adoption of phytochemicals in water treatment. The field of phytobiotics should engage modern methodologies such as proteomics, genomics, and metabolomics to minimise challenges confronting phytobiotic standardisation. The knowledge disseminated awaits novel application for plant product development in water treatment.

Effect of lemongrass essential oil against multidrug-resistant Salmonella Heidelberg and its attachment to chicken skin and meat

Salmonella Heidelberg (S. Heidelberg) is a major pathogen implicated in foodborne outbreaks for which poultry products can serve as an epidemiological source. This study determined the efficacy of GRAS-status lemongrass essential oil (LGEO) against S. Heidelberg in vitro and on the pathogen's attachment to skin and meat. At first, employing in vitro assays, the effect of LGEO on multidrug-resistant S. Heidelberg multiplication and motility was examined. Biofilm inhibition and inactivation assays were also performed. The quorum-sensing modulating effect of LGEO was determined. In follow-up experiments, chicken skin or meat samples inoculated with S. Heidelberg were treated with various concentrations of LGEO at different time points at simulated scalding (54°C) and chilling (4°C) temperatures. The samples were incubated, and the surviving populations of S. Heidelberg were enumerated to determine if LGEO could be a potential processing aid in poultry operations. Duplicate samples were included in each treatment, and the experiments were repeated at least 3 times. Significant reductions of S. Heidelberg of at least 4.0 log₁₀ CFU/mL after 24 h in nutrient broth and poultry cecal contents was observed with 0.5% LGEO. Complete inhibition of motility, biofilm formation, and inactivation of pre-formed biofilms was observed with 0.15% LGEO (P ≤ 0.05). Concentrations of LGEO at 0.5% and 1% affected violacein production (P ≤ 0.05). On skin samples, all concentrations significantly reduced S. Heidelberg by 1.2 to 3.9 log₁₀ CFU/sample after 2 min at 54°C. We obtained a significant reduction of the pathogen in meat samples at 54°C and skin samples at 4°C with 2% LGEO. All concentrations significantly reduced S. Heidelberg from the treatment water kept at 4°C and 54°C (P ≤ 0.05). In conclusion, LGEO could potentially serve as a natural antimicrobial strategy in scalding and chilling waters to reduce S. Heidelberg during processing. However, additional studies are warranted before recommending its commercial use.

Advanced Killing Potential of Thymol against a Time and Temperature Optimized Attached Listeria monocytogenes Population in Lettuce Broth

Fresh vegetables and salads are increasingly implicated in outbreaks of foodborne infections, such as those caused by Listeria monocytogenes, a dangerous pathogen that can attach to the surfaces of the equipment creating robust biofilms withstanding the killing action of disinfectants. In this study, the antimicrobial efficiency of a natural plant terpenoid (thymol) was evaluated against a sessile population of a multi-strain L. monocytogenes cocktail developed on stainless steel surfaces incubated in lettuce broth, under optimized time and temperature conditions (54 h at 30.6 °C) as those were determined following response surface modeling, and in comparison, to that of an industrial disinfectant (benzalkonium chloride). Prior to disinfection, the minimum bactericidal concentrations (MBCs) of each compound were determined against the planktonic cells of each strain. The results revealed the advanced killing potential of thymol, with a concentration of 625 ppm (= 4 × MBC) leading to almost undetectable viable bacteria (more than 4 logs reduction following a 15-min exposure). For the same degree of killing, benzalkonium chloride needed to be used at a concentration of at least 20 times more than its MBC (70 ppm). Discriminative repetitive sequence-based polymerase chain reaction (rep-PCR) also highlighted the strain variability in both biofilm formation and resistance. In sum, thymol was found to present an effective anti-listeria action under environmental conditions mimicking those encountered in the salad industry and deserves to be further explored to improve the safety of fresh produce.

Antimicrobial and anti-biofilm effects of probiotic Lactobacillus plantarum KU200656 isolated from kimchi

The probiotic properties and anti-pathogenic effects of Lactobacillus plantarum KU200656 (KU200656) isolated from Korean fermented kimchi against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium were investigated. KU200656 showed high tolerance to artificial gastric acid (99.48%) and bile salts (102.40%) and this strain was safe according to antibiotic sensitivity test; it could not produce harmful enzymes, including β-glucuronidase. KU200656 exhibited high adhesion (4.45%) to intestinal cells, HT-29 cells, with high cell surface hydrophobicity (87.31% for xylene and 81.11% for toluene). Moreover, KU200656 co-aggregated with pathogenic bacteria and exhibited antibacterial activity and anti-adhesion properties against pathogens. The cell-free supernatant (CFS) of KU200656 inhibited biofilm formation by pathogenic bacteria. In addition, half of the minimum inhibitory concentration of the KU200656 CFS downregulated the expression of biofilm-related genes, as determined by quantitative real-time PCR. Therefore, KU200656 was demonstrated to possess anti-pathogenic effects and have potential for use as probiotics in the food industry.

The Interactions between Polyphenols and Microorganisms, Especially Gut Microbiota

This review presents the comprehensive knowledge about the bidirectional relationship between polyphenols and the gut microbiome. The first part is related to polyphenols' impacts on various microorganisms, especially bacteria, and their influence on intestinal pathogens. The research data on the mechanisms of polyphenol action were collected together and organized. The impact of various polyphenols groups on intestinal bacteria both on the whole "microbiota" and on particular species, including probiotics, are presented. Moreover, the impact of polyphenols present in food (bound to the matrix) was compared with the purified polyphenols (such as in dietary supplements) as well as polyphenols in the form of derivatives (such as glycosides) with those in the form of aglycones. The second part of the paper discusses in detail the mechanisms (pathways) and the role of bacterial biotransformation of the most important groups of polyphenols, including the production of bioactive metabolites with a significant impact on the human organism (both positive and negative).

Inhibition of Biofilm Formation and Related Gene Expression of Listeria monocytogenes in Response to Four Natural Antimicrobial Compounds and Sodium Hypochlorite

The aim of this study was to assess the efficacy of four natural antimicrobial compounds (cinnamaldehyde, eugenol, resveratrol and thymoquinone) plus a control chemical disinfectant (sodium hypochlorite) in inhibiting biofilm formation by Listeria monocytogenes CMCC54004 (Lm 54004) at a minimum inhibitory concentration (MIC) and sub-MICs. Crystal violet staining assay and microscopic examination were employed to investigate anti-biofilm effects of the evaluated compounds, and a real-time PCR assay was used to investigate the expression of critical genes by Lm 54004 biofilm. The results showed that five antimicrobial compounds inhibited Lm 54004 biofilm formation in a dose dependent way. Specifically, cinnamaldehyde and resveratrol showed better anti-biofilm effects at 1/4 × MIC, while sodium hypochlorite exhibited the lowest inhibitory rates. A swimming assay confirmed that natural compounds at sub-MICs suppressed Lm 54004 motility to a low degree. Supporting these findings, expression analysis showed that all four natural compounds at 1/4 × MIC significantly down-regulated quorum sensing genes (agrA, agrC, and agrD) rather than suppressing the motility- and flagella-associated genes (degU, motB, and flaA). This study revealed that sub-MICs of natural antimicrobial compounds reduced biofilm formation by suppressing the quorum sensing system rather than by inhibiting flagella formation.

Inhibition of Bacterial Biofilm Formation by Phytotherapeutics with Focus on Overcoming Antimicrobial Resistance

Bacteria within biofilms are more resistant to antibiotics and chemical agents than planktonic bacteria in suspension. Treatment of biofilm-associated infections inevitably involves high dosages and prolonged courses of antimicrobial agents; therefore, there is a potential risk of the development of antimicrobial resistance (AMR). Due to the high prevalence of AMR and its association with biofilm formation, investigation of more effective anti-biofilm agents is required. From ancient times, herbs and spices have been used to preserve foods, and their antimicrobial, anti-biofilm and anti-quorum sensing properties are well known. Moreover, phytochemicals exert their anti-biofilm properties at sub-inhibitory concentrations without providing the opportunity for the emergence of resistant bacteria or harming the host microbiota. With increasing scientific attention to natural phytotherapeutic agents, numerous experimental investigations have been conducted in recent years. The present paper aims to review the articles published in the last decade in order to summarize a) our current understanding of AMR in correlation with biofilm formation and b) the evidence of phytotherapeutic agents against bacterial biofilms and their mechanisms of action. The main focus has been put on herbal anti-biofilm compounds tested to date in association with Staphylococcus aureus, Pseudomonas aeruginosa and food-borne pathogens (Salmonella spp., Campylobacter spp., Listeria monocytogenes and Escherichia coli).

Natural Plant-Derived Chemical Compounds as Listeria monocytogenes Inhibitors In Vitro and in Food Model Systems

Listeria monocytogenes is a foodborne pathogen, sporadically present in various food product groups. An illness caused by the pathogen, named listeriosis, has high fatality rates. Even though L. monocytogenes is resistant to many environmental factors, e.g., low temperatures, low pH and high salinity, it is susceptible to various natural plant-derived antimicrobials (NPDA), including thymol, carvacrol, eugenol, trans-cinnamaldehyde, carvone S, linalool, citral, (E)-2-hexenal and many others. This review focuses on identifying NPDAs active against L. monocytogenes and their mechanisms of action against the pathogen, as well as on studies that showed antimicrobial action of the compounds against the pathogen in food model systems. Synergistic action of NDPA with other factors, biofilm inhibition and alternative delivery systems (encapsulation and active films) of the compounds tested against L. monocytogenes are also summarized briefly.

Decreased biofilm formation by planktonic cells of Listeria monocytogenes in the presence of sodium hypochlorite

The objective of this study was to determine if the adaptation at planktonic stage to subinhibitory concentrations (SIC) of sodium hypochlorite (NaOCl) could modulate the biofilm forming ability of five Listeria monocytogenes strains V7, Scott A, FSL-N1-227, FSL F6-154 and ATCC 19116 representing serotypes 1/2a, 4b and 4c. Biofilm formation by NaOCl nonadapted and adapted L. monocytogenes planktonic cells was measured in the presence or absence of SIC of NaOCl. The biofilm formation ability of NaOCl nonadapted and adapted L. monocyotgenes planktonic cells was reduced only in the presence of NaOCl (P < 0.05). Scanning electron microscopy revealed that the continuous exposure of NaOCl induced morphological changes in the L. monocytogenes biofilm structure and reduced its attachment to polystyrene surface. The qRT-PCR results also showed that the subinhibitory NaOCl reduced biofilm formation related gene expression such as motility and quorum sensing signals (P < 0.05). These findings indicate that subinhibitory NaOCl can reduce the ability of L. monocytogenes planktonic cells to form biofilms on polystyrene surface.

Application of bioactive glycolipids to control Listeria monocytogenes biofilms and as post-lethality contaminants in milk and cheese

Listeria monocytogenes can form persistent biofilms on food processing surfaces, resulting in cross-contamination of food products, including milk and milk products. Natural glycolipids are a promising intervention to control undesirable microbes due to their antimicrobial activity and low toxicity. This study aimed to determine the antimicrobial activity of glycolipids to control L. monocytogenes biofilms as well as in milk and on Queso Fresco. Application of a natural glycolipid product significantly reduced biofilm-associated L. monocytogenes on both polystyrene and stainless steel at concentrations as low as 45 mg/L. When added to UHT skim milk, a concentration of 1000 mg/L inhibited L. monocytogenes growth through 7 days of storage at 7 °C, and application of 1300 and 1500 mg/L reduced counts to levels below the limit of enumeration at day 21. In contrast, 2000 mg/L were necessary to inhibit growth through 7 days in whole milk. Glycolipid solutions at concentrations ≥10% reduced L. monocytogenes counts on Queso Fresco through 7 days when applied as a dip. Overall, natural glycolipids have potential as a natural alternative for the removal of biofilms and as an antimicrobial to control L. monocytogenes in milk and milk products with short shelf lives.

Synergistic interactions of plant essential oils with antimicrobial agents: a new antimicrobial therapy

The problem of drug resistance of food borne pathogens is becoming more and more serious. Although traditional antimicrobial agents have good therapeutic effects on a variety of food borne pathogens, more effective antimicrobial agents are still needed to combat the development of drug-resistant food borne pathogens. Plant-based natural essential oils (EOs) are widely used because of their remarkable antimicrobial activity. A potential strategy to address food borne pathogens drug resistance is to use a combination of EOs and antimicrobial agents. Because EOs have multi-target inhibitory effects on microorganisms, combining them with drugs can enhance the activity of the drugs and avoid the emergence of food borne pathogens drug resistance. This paper introduces the main factors affecting the antibacterial activity of EOs and describes methods for evaluating their synergistic antibacterial effects. The possible mechanisms of action of EOs and the synergistic inhibitory effects on pathogens of EOs in combination with antimicrobial agents is described. In summary, the combined use of EOs and existing antimicrobial agents is a promising potential new antibacterial therapy.

Bacterial Resistance: Antibiotics of Last Generation used in Clinical Practice and the Arise of Natural Products as New Therapeutic Alternatives

Bacterial resistance to therapeutical drugs has been a serious issue over the last decades. In fact, the quick development of resistance mechanisms by the microorganisms has been fatal for millions of people around the world, turning into a public health issue. The major cause of the resistance mechanisms is the overuse of antimicrobials. European countries try to implement mechanisms to overcome antimicrobial resistance in the community through the rational use of antimicrobials. The scientific community has been exhaustively dedicated to the discovering of new, safer and efficient drugs, being the exploitation of natural resources, mainly plants and fungi, considered as a hot topic in the field of antimicrobial agents. Innumerous reports have already shown the promising capacity of natural products or molecules extracted from these natural resources, to act as bacteriostatic and bactericidal agents. More importantly, these natural agents present significantly lower harmful effects. Bearing that in mind, this review aims at giving a contribution to the knowledge about the synthetic antibiotics of the last generation. Moreover, it is intended to provide information about the last advances regarding the discovery of new antimicrobial agents. Thus, a compilation of the chemical characteristics, efficiency, harmful outcomes and resistance mechanisms developed by the microorganisms can be consulted in the following sections together with a critical discussion, in line with the recent approaches. Furthermore, modern strategies for the prospection of novel anti-infective compounds for tackling resistant bacteria have been considered as also a current synopsis of plants and mushrooms with relevant antimicrobial potentials.

The Potential of Plant-Based Bioactive Compounds on Inhibition of Aflatoxin B1 Biosynthesis and Down-regulation of aflR, aflM and aflP Genes

The use of plant extracts in pre- and post-harvest disease management of agricultural crops to cope with aflatoxin B1 contamination has shown great promise due to their capability in managing toxins and safe-keeping the quality. We investigated the anti-aflatoxigenic effect of multiple doses of eight plant extracts (Heracleum persicum, Peganum harmala, Crocus sativus, Trachyspermum ammi, Rosmarinus officinalis, Anethum graveolens, Berberis vulgaris, Berberis thunbergii) on Aspergillus flavus via LC-MS and the down-regulatory effect of them on aflR, aflM and aflP genes involved in the aflatoxin B1 biosynthesis pathway using RT-qPCR analyses. Our results showed that H. persicum (4 mg/mL), P. harmala (6 mg/mL) and T. ammi (2 mg/mL) completely stopped the production of aflatoxin B1, without inducing significant changes in A. flavus growth. Furthermore, our findings showed a highly significant correlation between the gene expression and the aflatoxin B1 biosynthesis, such that certain doses of the extracts reduced or blocked the expression of the aflR, aflM and aflP and consequently reduced the synthesis of aflatoxin B1. Interestingly, compared to the regulatory gene (aflR), the down-regulation of expression in the structural genes (aflM and aflP) was more consistent and correlated with the inhibition of aflatoxin B1 production. Overall, this study reveals the anti-aflatoxigenic mechanisms of the selected plant extracts at the gene expression level and provides evidence for their use in plant and crop protection.

(-)-Tetrahydroberberrubine∙acetate accelerates antioxidant potential and inhibits food associated Bacillus cereus in rice

A protoberberine alkaloid, (-)-tetrahydroberberrubine∙acetate (THBA) was assessed for its antioxidant potential and ability to inhibit the growth of a food hazard bacterium Bacillus cereus in vitro and in situ. THBA displayed significant and dose-dependent cellular antioxidant potential against hydrogen peroxide-induced oxidative stress in NIH 3T3 fibroblast cells and decreased the ROS levels as well as increased the expression levels of SOD1 and SOD2 enzymes. The inhibitory spectrum of THBA confirmed its mechanistic role in the disruption of the membrane integrity of B. cereus as evidenced by the results of time-inactivation, cell membrane integrity, NPN membrane uptake, membrane potential, and electron microscopy analyses. Moreover, THBA inhibited biofilm formation by B. cereus and disrupted pre-established biofilms on a glass surface. Furthermore, THBA was also able to inhibit B. cereus in raw rice with a significant amount of reduction in CFU counts, suggesting its potential role as a natural antioxidant and antimicrobial agent.

Plant-Based Phytochemicals as Possible Alternative to Antibiotics in Combating Bacterial Drug Resistance

The unprecedented use of antibiotics that led to development of resistance affect human health worldwide. Prescription of antibiotics imprudently and irrationally in different diseases progressed with the acquisition and as such development of antibiotic resistant microbes that led to the resurgence of pathogenic strains harboring enhanced armors against existing therapeutics. Compromised the treatment regime of a broad range of antibiotics, rise in resistance has threatened human health and increased the treatment cost of diseases. Diverse on metabolic, genetic and physiological fronts, rapid progression of resistant microbes and the lack of a strategic management plan have led researchers to consider plant-derived substances (PDS) as alternative or in complementing antibiotics against the diseases. Considering the quantitative characteristics of plant constituents that attribute health beneficial effects, analytical procedures for their isolation, characterization and phytochemical testing for elucidating ethnopharmacological effects has being worked out for employment in the treatment of different diseases. With an immense potential to combat bacterial infections, PDSs such as polyphenols, alkaloids and tannins, present a great potential for use, either as antimicrobials or as antibiotic resistance modifiers. The present study focuses on the mechanisms by which PDSs help overcome the surge in resistance, approaches for screening different phytochemicals, methods employed in the identification of bioactive components and their testing and strategies that could be adopted for counteracting the lethal consequences of multidrug resistance.

Common Plant-Derived Terpenoids Present Increased Anti-Biofilm Potential against Staphylococcus Bacteria Compared to a Quaternary Ammonium Biocide

The antimicrobial actions of three common plant-derived terpenoids (i.e., carvacrol, thymol and eugenol) were compared to those of a typical quaternary ammonium biocide (i.e., benzalkonium chloride; BAC), against both planktonic and biofilm cells of two widespread Staphylococcus species (i.e., S. aureus and S. epidermidis). The minimum inhibitory and bactericidal concentrations (MICs, MBCs) of each compound against the planktonic cells of each species were initially determined, together with their minimum biofilm eradication concentrations (MBECs). Various concentrations of each compound were subsequently applied, for 6 min, against each type of cell, and survivors were enumerated by agar plating to calculate log reductions and determine the resistance coefficients (Rc) for each compound, as anti-biofilm effectiveness indicators. Sessile communities were always more resistant than planktonic ones, depending on the biocide and species. Although lower BAC concentrations were always needed to kill a specified population of either cell type compared to the terpenoids, for the latter, the required increases in their concentrations, to be equally effective against the biofilm cells with respect to the planktonic ones, were not as intense as those observed in the case of BAC, presenting thus significantly lower Rc. This indicates their significant anti-biofilm potential and advocate for their further promising use as anti-biofilm agents.

Essential Oils of Aromatic Plants with Antibacterial, Anti-Biofilm and Anti-Quorum Sensing Activities against Pathogenic Bacteria

Both the ability of bacteria to form biofilms and communicate through quorum sensing allows them to develop different survival or virulence traits that lead to increased bacterial resistance against conventional antibiotic therapy. Here, seventeen essential oils (EOs) were investigated for the antimicrobial, antibiofilm, and anti-quorum sensing activities on Escherichia. coli O157:H7, Escherichia coli O33, and Staphylococcus epidermidis ATCC 12228. All essential oils were isolated from plant material by using hydrodistillation and analyzed by GC-MS. The antimicrobial activity was performed by using the microdilution technique. Subinhibitory concentrations of each EO were assayed for biofilm inhibition in both bacterial strains. Quantification of violacein in Chromobacterium violaceum CV026 was performed for the anti-quorum sensing activity. The cytotoxicity activity of the EOs was evaluated on Vero cell line by using MTT method. Thymol-carvacrol-chemotype (I and II) oils from Lippia origanoides and Thymus vulgaris oil exhibited the higher antimicrobial activity with MIC values of 0.37-0.75 mg/mL. In addition, these EOs strongly inhibited the biofilm formation and violacein (QS) production in a concentration-dependent manner, highlighting thymol-carvacrol-chemotype (II) oil as the best candidate for further studies in antibiotic design and development against bacterial resistance.

Rugose Morphotype in Salmonella Typhimurium and Salmonella Heidelberg Induced by Sequential Exposure to Subinhibitory Sodium Hypochlorite Aids in Biofilm Tolerance to Lethal Sodium Hypochlorite on Polystyrene and Stainless Steel Surfaces

Salmonella biofilms act as a continuous source for cross-contamination in the food processing environments. In this study, a stable rugose morphotype of Salmonella was first induced by sequential exposure to subinhibitory concentrations (SICs) of sodium hypochlorite (NaOCl) (ranging from 50 to 300 ppm over 18-day period) in tryptic soy broth. Then, rugose and smooth morphotypes of Salmonella Typhimurium ATCC 14028 and Salmonella Heidelberg ATCC 8326 were characterized for biofilm forming abilities on polystyrene and stainless steel surfaces. Rugose morphotype of both ATCC 14028 and ATCC 8326 exhibited higher Exopolysaccharide (EPS) formation than smooth morphotype (p ≤ 0.05). Also, the SICs of NaOCl (200 or 300 ppm in broth model) increased the biofilm formation ability of rugose morphotype of ATCC 8326 (p ≤ 0.05) but decreased that of ATCC 14028. The 2-day-old Salmonella biofilms were treated with biocidal concentrations of 50, 100, or 200 ppm NaOCl (pH 6.15) in water for 5, 10, or 20 min at room temperature. The biofilm reduction in CFU/cm2 for the rugose was lower than the smooth morphotype on both surfaces (p ≤ 0.05) by lethal NaOCl in water. Scanning electron micrographs on both polystyrene and stainless steel surfaces demonstrated that the rugose morphotype produced a denser biofilm than the smooth morphotype. Transmission electron micrographs revealed the cell wall roughness in rugose morphotype, which may help in tolerance to NaOCl. The gene expression data indicate that the expression of biofilm regulator (csgD), curli (csgA, csgB, and csgC), and cellulose (bcsE) was significantly increased in rugose morphotype when induced by sequential exposure of NaOCl SICs. These findings reveal that the rugose morphotype of S. Typhimurium and S. Heidelberg produced significantly denser biofilm on food contact surfaces, which also increased with sequential exposure to SICs of NaOCl in the case of S. Heidelberg, and these biofilms were more tolerant to biocidal NaOCl concentrations commonly used in the food processing plants.