Gram-negative Foodborne Pathogens Research Articles

Comparative analysis of the application efficiency of gold nanoparticles-based SERS in four foodborne pathogenic microbes

It has been widely reported that SERS can detect foodborne pathogenic bacteria, but SERS has only been limited to the detection of purified single bacteria. However, there’s few single bacterial infections in the natural state were found at the most time, and rare comparative investigations of different Gram-negative and Gram-positive bacteria by SERS exist. At the present study, we are aiming at the comparative analysis of the detection efficiency toward different foodborne pathogenic microbes by a conventional citrate-reduced gold colloid, including Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Listeria monocytogenes. The SERS spectra of samples were collected with sterile 0.5% NaCl solution as aggregating compound. First, the stability of each bacterial were detected with gold nanoparticles. Afterward, SERS signals of the four bacteria were compared at different concentrations, and it was found that Gram-positive and Gram-negative bacteria have different minimum sensitivity and detection stability. Next, the mixed bacterial SERS detection was applied to classify and identify the similar Raman spectra. Spectral data were analyzed using multivariate data analysis methods, including principal component analysis (PCA) and hierarchical cluster analysis (HCA). The SERS procedure we proposed, which utilized gold nanoparticles adsorbing on bacteria and multivariate analysis, allowed differentiation of species. The results of this pilot study demonstrate the potential of SERS to rapidly identify Gram-negative and Gram-positive foodborne pathogens.

D-tryptophan, an eco-friendly natural, safe, and healthy compound with antimicrobial activity against food-borne pathogens: A systematic review.

Recently, the use of D-amino acids as food preservatives has attracted considerable attention because these natural compounds do not have adverse effects on human health. In addition, D-amino acids such as D-tryptophan can reduce the harmful effects of other treatments. For instance, the use of D-tryptophan in food reduces the requirement for high temperatures and their damaging effects on nutrients such as proteins and vitamins. The purpose of this systematic review was to investigate the antimicrobial effect of D-tryptophan on food-borne pathogens invitro and in food models. To identify related studies, scientific digital databases such as PubMed, Science Direct, and Google Scholar were searched from January 2000 to February 2023. The results of the studies showed that when D-tryptophan was used with other stresses such as using different salt concentrations, refrigeration, or high temperatures, it showed significant antimicrobial effects on Gram-positive and Gram-negative food-borne pathogens, and antibiofilm impacts were also observed with D-tryptophan. Since studies have shown that the antimicrobial activity of D-tryptophan depends on several factors, including the pathogen strain, the type of stress, and the concentration of D-tryptophan, and every article has focused on one of these factors, there is a need for a systematic review that summarizes and concludes the effect of all these factors on the antimicrobial activity of D-tryptophan against food-borne pathogens.

Inhibition of Food-Borne Pathogen Growth and Biogenic Amine Synthesis by Spice Extracts

Food-borne pathogens and their toxins cause significant health problems in humans. Formation of biogenic amines (BAs) produced by microbial decarboxylation of amino acids in food is undesirable because it can induce toxic effects in consumers. Therefore, it is crucial to investigate the effects of natural additives with high bioactivity like spice extracts to inhibit the growth of these bacteria and the formation of BAs in food. In the present study, the antibacterial effects of diethyl ether spice (sumac, cumin, black pepper, and red pepper) extracts at doses of 1% (w/v) on Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Klebsiella pneumoniae, Pseudomonas aeruginosa, Campylobacter jejuni, Aeromonas hydrophila, Salmonella Paratyphi A, and Yersinia enterocolitica) food-borne pathogen bacterial strains (FBP) were established. In addition, the accumulation of ammonia (AMN), trimethylamine (TMA), and biogenic amines (BAs) in tyrosine decarboxylase broth (TDB) was investigated by using high performance liquid chromatography (HPLC). Sumac extract exhibited the highest antibacterial potential against all FBPs, followed by cumin and peppers. AMN (570.71 mg/L) and TMA (53.66 mg/L) production were strongly inhibited by sumac extract in the levels of 55.10 mg/L for Y. enterocolitica and 2.76 mg/L for A. hydrophila, respectively. With the exception of S. aureus, black pepper dramatically reduced the synthesis of putrescine, serotonin, dopamine, and agmatine by FBP especially for Gram-negative ones. Furthermore, sumac extracts inhibited histamine and tyramine production by the majority of FBP. This research suggests the application of sumac extracts as natural preservatives for inhibiting the growth of FBPs and limiting the production of AMN, TMA, and BAs.

Effects and molecular mechanism of sugar transporter ESA_RS15745 on desiccation resistance, motility, and biofilm formation of Cronobacter sakazakii.

Cronobacter sakazakii, an important Gram-negative foodborne pathogen, can cause neonatal meningitis and sepsis with high rates of infection and death. Gene ESA_RS15745 encodes a sugar transporter protein, which is not only essential for osmotic pressure maintenance during bacterial growth and reproduction but also associated with their desiccation tolerance, motility, and biofilm formation. Here, a mutant strain of ESA_RS15745 (ΔESA_RS15745) and the complementation strain (cpESA_RS15745) were constructed using a suicide vector knockout and gene complementation. ΔESA_RS15745 was found to have a decrease in its ability to transport maltose and trehalose and resist desiccation, whereas an increase in the ability of motility and biofilm formation, implying that ESA_RS15745 may positively regulate sugar transport and desiccation tolerance and negatively regulate motility and biofilm formation. To further investigate the molecular mechanisms underlying the function of related genes, RNA-seq was performed to explore the differentially expressed genes in the mutants. RNA-seq results showed the upregulation of 114 genes (mainly including those regulating chemotaxis and flagellar motility) and the downregulation of 22 genes (mainly including those regulating sugar transport). qRT-PCR analysis supported the RNA-seq results and showed that ESA_RS15745 may influence the dehydration tolerance though decreasing the intracellular trehalose content and negatively regulate the motility though the chemotactic signaling pathway. In addition, the biofilm formation of C. sakazakii should also be speculated to negatively regulate by ESA_RS15745 by consuming the extracellular carbohydrates concentration and then downregulating the intracellular cyclic diguanosine monophosphate. This study offers a reference for comprehending the molecular mechanism of gene ESA_RS15745 in C. sakazakii.

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

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

Identification of VP0143 gene which modulates biofilm formation of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a Gram-negative halophilic foodborne pathogen associated with seafood consumption and can cause acute inflammatory gastroenteritis. The biofilm formed by V. parahaemolyticus facilitates its colonization and persistence in the food production chain, posing a continuous threat to food safety. In this study, through transposon mutants screening, we identified a novel gene, VP0143, which positively regulated biofilm formation of V. parahaemolyticus. The VP0143 deletion mutant (ΔVP0143) exhibited less biofilm formation as determined by crystal violet staining assay and showed decreased viability of biofilm cells by XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay compared to the wild type strain. The ΔVP0143 strain also showed weakened flagella-mediated motility and surface hydrophobicity. Moreover, VP0143 deletion significantly affected the production of autoinducer-2 and exopolysaccharides in biofilm, and reduced Raman peak intensity of biofilm components. Microscopic analysis confirmed that biofilm formed by ΔVP0143 strain showed loosened structure. In addition, ΔVP0143 strain exhibited compromised ability to form biofilm on silicon wafers, glass and stainless-steel plates, as well as on shrimp and crab surfaces. All these defects were reversed in the complementation strain ΔVP0143C. RT-qPCR further indicated that expression of genes associated with biofilm formation was decreased after VP0143 deletion. Therefore, our data suggest that VP0143 is involved in regulating biofilm formation of V. parahaemolyticus and extend our understanding of genetic determinants of V. parahaemolyticus biofilm formation.

Isolation, antibacterial characterization, and alternating tangential flow–based preparation of viable cells of Lacticaseibacillus paracasei XLK 401: Potential application in milk preservation

It is desirable to obtain high levels of viable Lacticaseibacillus paracasei, a widely used food probiotic whose antibacterial activity and potential application in milk remain largely uninvestigated. Here, we isolated and purified the L. paracasei strain XLK 401 from food-grade blueberry ferments and found that it exhibited strong antibacterial activity against both gram-positive and gram-negative foodborne pathogens, including Staphylococcus aureus, Salmonella paratyphi B, Escherichia coli O157, and Shigella flexneri. Then, we applied alternating tangential flow (ATF) technology to produce viable L. paracasei XLK 401 cells and its cell-free supernatant (CFS). Compared with the conventional fed-batch method, 22 h of ATF-based processing markedly increased the number of viable cells of L. paracasei XLK 401 to 12.14 ± 0.13 log cfu/mL. Additionally, the CFS exhibited good thermal stability and pH tolerance, inhibiting biofilm formation in the abovementioned foodborne pathogens. According to liquid chromatography-mass spectrometry analysis, organic acids were the main antibacterial components of XLK 401 CFS, accounting for its inhibition activity. Moreover, the CFS of L. paracasei XLK 401 effectively inhibited the growth of multidrug-resistant gram-positive Staph. aureus and gram-negative E. coli O157 pathogens in milk, and caused a reduction in the pathogenic cell counts by 6 to 7 log cfu/mL compared with untreated control, thus considerably maintaining the safety of milk samples. For the first time to our knowledge, ATF-based technology was employed to obtain viable L. paracasei on a large scale, and its CFS could serve as a broad-spectrum biopreservative for potential application against foodborne pathogens in milk products.

Grafting bacterial cellulose nanowhiskers into whey protein/essential oil film composites: Effect on structure, essential oil release and antibacterial properties of films

The development of bio-based primary packaging is imperative to improve food safety and quality, along with mitigating the environmental pollution resulting from the increasing production of packaging wastes. Whey protein concentrate (WPC) has received significant attention as an alternative raw material for edible films production, whereas an area of many ongoing researches has been the inclusion of bio-based compounds to formulate functional edible films. This study elaborated the development of WPC edible films fortified with different essential oils (EO) to assess antimicrobial activity against gram-positive (Staphylococcus aureus and Listeria monocytogenes) and gram-negative (Salmonella enteritidis and Pseudomonas aeruginosa) food-borne pathogens. Subsequently, the effect of grafting bacterial cellulose nanowhiskers (BCNW) in film composites was evaluated for WPC/oregano EO (WPC/OEO) films, which showed the highest antibacterial activity. Notably, increasing the concentration of grafted BCNW entailed a proportional increase on the inhibitory activity. In specific, antibacterial activity increased up to 80% when 10% BCNW was grafted in WPC/OEO films. Inclusion of BCNW and homogenous distribution of OEO into the film blend was pointed out through Raman analysis. In addition, AFM and SEM analysis revealed that inclusion of BCNW and OEO into the film matrix led to the formation of rough films with pores. This structural change enhanced the release capacity of OEO, that was further confirmed through a release kinetic experiment. This study indicated that BCNW addition positively affected whey protein films properties, thereby envisaging the potential development of sustainable food packaging materials with tailor-made properties.

Inhibitory effect of resveratrol on swimming motility and adhesion ability against Salmonella enterica serovar Typhimurium infection

Salmonella enterica serovar Typhimurium (S. typhimurium) is a common Gram-negative foodborne pathogen that threatens public health and hinders the development of livestock industry. Resveratrol, an important component in grape fruits and seeds, has been shown to possess multiple biological activities, but its potential effects on S. typhimurium-mediated virulence have been rarely reported. In this study, we investigated the effect of resveratrol on S. typhimurium flagella -mediated virulence. The results showed that resveratrol significantly reduced the transcription of flagella genes and swimming motility of S. typhimurium, and also inhibited the transcription of T3SS-related virulence genes with varying degrees inhibiting bacterial growth. Simultaneously, resveratrol significantly reduced the adhesion of S. typhimurium to HeLa cells. Unfortunately, resveratrol does not improve the survival rate of S. typhimurium-infected mice, but it reduces the bacterial load in the liver and spleen of infected mice, and it also has a certain degree of anti-inflammatory activity. In summary, these results indicated that resveratrol has the potential to be developed as an alternative drug or antibacterial agent to prevent Salmonella infection.

Inactivation of Salmonella enteritidis on the surface of eggs by air activated with gliding arc discharge plasma

Salmonella enteritidis, a Gram-negative foodborne pathogen, causes inflammation of the stomach and intestines. Poultry and poultry products are considered to be the main hosts of S. enteritidis, especially the most common edible eggs, and increase the risk of Salmonella infection. Therefore, developing the inactivation strategy of S. enteritidis on the surface of eggs is the key step during the egg production process. Gas plasma could effectively inactivate bacteria and fungi and is developed as a potential non-thermal sterilization method in the food industry. In this study, the plasma-activated air (PAA) prepared by the air activated with gliding arc discharge contained a variety of reactive species. When the PAA activated at the power of 50 W and 100 W was inducted into the incubation chamber, the numbers of S. enteritidis on egg fragments or the whole eggs were reduced below the detection limit. After PAA treatment, the eggshells exhibited no change in structure demonstrated by scanning electron microscope, the color of eggshells became a little decrease in red, the internal quality of both the raw egg and the cooked egg also exhibited no change, and trace reactive species remained in the albumen. Further, the PAA was also feasible for the batch treatment of stacked eggs. Therefore, this study supplied an effective and safe strategy for aseptic processing in the poultry industry.

Antimicrobial Activities and Biopreservation Potential of Lactic Acid Bacteria (LAB) from Raw Buffalo (Bubalus bubalis) Milk.

The aim of this study was to investigate the antimicrobial and biopreservation potential of lactic acid bacteria. The potential probiotic culture inhibited the growth of gram-positive and gram-negative foodborne pathogens in agar spot assay with inhibition zones ranging from 10 to 21 mm in diameter. The strains showed coaggregation capabilities ranging from 7 to 71% with tested food pathogens including Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Salmonella enterica subsp. enterica serovar Typhimurium. The effect of cell-free supernatants on the release of 260 nm absorbing material, especially nucleic acids, was evaluated and indicated the antagonistic activity on foodborne pathogens, the highest being Lactobacillus paraplantarum against E. coli (3.77) and S. aureus (3.86) after 60 min. The effect of cell-free supernatant (CFS) on the growth of pathogens showed that Lactobacillus paraplantarum 11 and L. pentosus 93 had the highest inhibitory activity against tested strains. The biopreservation assay indicated that the potential probiotic strains Lactobacillus paraplantarum 11 (BT), Lactiplantibacillus plantarum 19, Lactobacillus pentosus 42, Limosilactobacillus fermentum 60, Lactobacillus pentosus 93, and Limosilactobacillus reuteri 112 were effective in reducing the Listeria monocytogenes population in raw buffalo milk. Complete Listeria monocytogenes inhibition was observed after 6-8 days. This study showed that probiotic LAB from buffalo milk have antimicrobial and biopreservation potential; these strains have the potential to be utilized as biopreservative agents in food products.

Diarrheagenic Escherichia coli and Their Antibiotic Resistance Patterns in Dairy Farms and Their Microbial Ecosystems

Ruminants are the largest reservoir for all types of Escherichia coli, including the pathogenic ones, which can potentially be transmitted to humans via the food chain and environment. A longitudinal study was performed to estimate the prevalence and antibiotic-resistant pattern of pathogenic E. coli (pE.coli) strains in dairy farm environments. A total of 846 environmental samples (water, lagoon slurry, bedding, feed, feces, soil, and compost) were collected in summer over two years from five dairy farms in Maryland, USA. An additional 40 soil samples were collected in winter and summer seasons for evaluating microbiome composition. Collected environmental samples were screened for the presence of pE.coli, which was isolated using a selective culture medium, for later confirmation and virotyping using PCR with specific primers. The overall prevalence of pE.coli in dairy farms was 8.93% (71/846), with the most common virotype identified in isolates being ETEC, followed by STEC. The highest pE.coli prevalence were recorded in lagoon slurry (21.57%) while the lowest was in compost heap (2.99%). Among isolates, 95.87% of the virotypes were resistant to 9 classes of antibiotics whereas only 4.12% were sensitive. The highest proportion (68.04%) of resistance was found for quinolones (e.g., ciprofloxacin). The resulting metagenomic analysis at the phylum and genus levels of the grazing land soil suggests that climatic conditions actively influence the abundance of bacteria. Proteobacteria, which contains many Gram-negative foodborne pathogens (including pE.coli), was the most predominant phylum, accounting for 26.70% and 24.93% of soil bacteria in summer and winter, respectively. In addition to relative abundance, there was no significant difference in species diversity between seasons when calculated via Simpson (D) and Shannon (H) index. This study suggests that antibiotic-resistant E. coli virotypes are present in the dairy farm environment, and proper steps are warranted to control its transmission irrespective of seasonality.

A novel bacteriocin against multiple foodborne pathogens from Lacticaseibacillus rhamnosus isolated from juice ferments: ATF perfusion-based preparation of viable cells, characterization, antibacterial and antibiofilm activity

Foodborne pathogens and their biofilms pose a risk to human health through food chain. However, the bacteriocin resources combating this threat are still limited. Here, Lacticaseibacillus rhamnosus, one of the most used probiotics in food industry, was prepared on a large scale using alternating tangential flow (ATF) perfusion-based technology. Compared to the conventional fed-batch approach, ATF perfusion remarkably increased the viable cells of L. rhamnosus CLK 101 to 11.93 ± 0.14 log CFU/mL. Based on obtained viable cells, we purified and characterized a novel bacteriocin CLK_01 with a broad spectrum of activity against both Gram-positive and Gram-negative foodborne pathogens. LC-MS/MS analysis revealed that CLK_01 has a molecular mass of 701.49 Da and a hydrophobic amino acid composition of I–K–K–V-T-I. As a novel bacteriocin, CLK_01 showed high thermal stability and acid-base tolerance over 25–121 °C and pH 2–10. It significantly reduced cell viability of bacterial pathogens (p < 0.001), and strongly inhibited their biofilm formation. Scanning electron microscopy demonstrated deformation of pathogenic cells caused by CLK_01, leading to cytoplasmic content leakage and bacterial death. Summarily, we employed ATF perfusion to obtain viable L. rhamnosus, and presented that bacteriocin CLK_01 could serve as a promising biopreservative for controlling foodborne pathogenic bacteria and their biofilms.

Systematic Surveillance and Meta-Analysis of Antimicrobial Resistance and Food Sources from China and the USA.

Since the discovery of antibiotics in the 20th century, they have been used to fight against infections. The overuse of antibiotics in the wider environment has resulted in the emergence of multidrug-resistant bacteria. In developing countries such as China and developed countries such as the USA, there is evidence of the high pervasiveness of antibiotic-resistant infections. However, the studies on the spread of antibiotic-resistant microorganisms that inform about the consequences are limited. The aim of our study was to analyze and compare antimicrobial resistance (AMR) identified in published research papers from that found in different food sources, which were published between 2012 and December 2021, covering most retail food items. Out of 132 research papers identified, 26 papers have met our strict criteria and are included in the qualitative and quantitative analysis. The selected papers led to 13,018 food samples, out of which 5000 samples were contaminated, including 2276 and 2724 samples from China and the USA, respectively. Meat, aquatic products, milk, and eggs show high to medium potential for AMR exposure to Gram-positive bacteria such as Staphylococcus, Enterococci, etc. and Gram-negative foodborne pathogens such as Campylobacter, Salmonella, Vibrio, etc. Most of the food samples show antibiotic resistance to β-lactams, tetracycline, quinolones, and aminoglycosides. Retail food products such as meat, sea food, and some other food products, as well as AMR genetics and technically important bacteria, are proposed to be better merged with mitigation strategies and systematic One Health AMR surveillance to minimize the knowledge gaps and facilitate comprehensive AMR risk computation for the consumers.

Synergistic antibacterial activity of compact silver/magnetite core-shell nanoparticles core shell against Gram-negative foodborne pathogens.

The development of innovative antibacterial drugs against foodborne pathogens has led to an interest in novel materials such as nanomaterials. The unique features of nanomaterial qualify it for use as an antibacterial treatment. Noble metals and metal oxide nanoparticles, such as silver and magnetite nanoparticles, have been shown to be effective antibacterial medications against a range of microorganisms. In this work, Ag@Fe3O4 -NPs were fabricated by using a wet chemical reduction and modified co-precipitation techniques. The antibacterial efficiency of the Ag/Fe3O4 core shell nanoparticles was investigated by applying various techniques, such as the Kirby–Bauer Disk Diffusion test, minimum inhibitory concentration (MIC) and bactericidal concentration (MBC), Colony Forming Unit (CFU), and kill time assay. The toxicity mechanism of Ag@Fe3O4 -NPs against Salmonella typhimurium and Escherichia coli was studied by apoptosis and reactive oxygen species (ROS) assays. The data revealed that a cubic core was surrounded by a silver shell, which indicated the regular morphology of silver magnetite core shell nanoparticles without any aggregation. Furthermore, Ag@Fe3O4 -NPs is more toxic against S. typhimurium and E. coli than Ag-NPs and Fe3O4 NPs. The MIC values for Ag/Fe3O4 NPs against S. typhimurium and E. coli were 3.1 and 5.4 μg/ml, respectively, whereas the MIC values for Ag-NPs and MNPs against S. typhimurium and E. coli were 4.1 and 8.2 μg/ml for Ag-NPs and 6.9 and 10.3 μg/ml for MNPs. The results showed the ability of Ag@Fe3O4 -NPs to induce apoptosis by generating ROS. Also, the ability of Ag@Fe3O4 -NPs to liberate free Ag+ and generate ROS via the Haber-Weiss cycle may be a plausible mechanism to explain the toxicity of Ag@Fe3O4 -NPs - NPs.

Effects of cinnamaldehyde against planktonic bacteria and biofilm formation of Shigella flexneri

Cinnamaldehyde (CA) has demonstrated anti-inflammatory, anti-tumor and anti-cancer activities; Its antimicrobial and antibiofilm actions against Shigella flexneri, on the other hand, have not been investigated. Sh. flexneri is a gram-negative foodborne pathogen that can be widely found in nature and some industrial production environments. In this current research, our aim was to examine the influences of CA on planktonic bacteria and biofilm formation. The minimum inhibitory concentration (MIC) of CA against Sh. flexneri strain was 100 μg/mL, while bacteria treated with CA showed a longer lag phase compared with the untreated control. CA effectively inactivated the Sh. flexneri in LB broth and fresh lettuce juice. CA treatment resulted in cell membrane permeability changes and dysfunction, as proven by cell membrane depolarization, decreased intracellular ATP concentration. In addition, CA was also discovered to increase the level of reactive oxygen species (ROS) in cells, and induce morphological changes in cells. Crystal violet staining showed that the biomass of biofilm was decreased significantly with CA in 24 h. Light microscopy and field emission scanning electron microscopy (FESEM) observations demonstrated decreased biofilm adhesion and destruction of biofilm architecture after treatment with CA. These findings indicated that CA acts as a natural bacteriostatic agent to control Sh. flexneri in food processing and production.

In Vitro Evaluation of Antimicrobial Effect of Phytobiotics Mixture on Salmonella spp. Isolated from Chicken Broiler.

Background: The identification of natural antibacterial agents from various sources that can act effectively against disease-causing foodborne bacteria is one of the major concerns throughout the world. In the present study, a unique phytobiotics mixture containing thymol, menthol, linalool, trans-anethole, methyl salicylate, 1,8-cineole, and p-cymene was evaluated for antibacterial activity against selected strains of Salmonella spp. Results: The phytobiotics mixture was effective against Salmonella enterica subsp. enterica serovars Enteritidis, Typhimurium, and Kentucky. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of this unique mixture for these three pathogens were 1:256. Among these three strains, one S. Kentucky presented the most extensive resistance profiles to 18 antibiotics belonging to 5 classes of antibiotics. One of S. Typhimurium presents extensive resistance profiles to 14 antibiotics belonging to 5 classes of antibiotics. Conclusions: The results suggest that the phytobiotics mixture used in the experiment can be used as a strong natural antibacterial agent against Gram-negative foodborne pathogens such as S. Typhimurium, S. Kentucky, and S. Enteritidis. This is a preliminary analysis of the effectiveness of a phytobiotic product in an in vitro model, which may be the starting point for further studies, including in vivo animal models.

Inactivation of Shigella flexneri by 405-nm Light-Emitting Diode Treatment and Possible Mechanism of Action.

Shigella flexneri, a common Gram-negative foodborne pathogen, is widely distributed in fresh-cut fruits and vegetables, unpasteurized milk, and food processing environments. The aims of this study were to evaluate the antibacterial effects of 405-nm light-emitting diode (LED) treatment on S. flexneri and to investigate the possible mechanism. The results showed that LED irradiation (360 min) reduced the number of S. flexneri in phosphate-buffered saline by 3.29 log colony-forming unit (CFU)/mL (initial bacterial count: 6.81 log CFU/mL). The cells in reconstituted infant formula, cells on fresh-cut carrot slices, and biofilm-associated cells on stainless steel surfaces were reduced by 1.83 log CFU/mL, 7.00 log CFU/cm2, and 4.35 log CFU/cm2 following LED treatment for 360, 120, and 120 min, respectively. LED treatment damaged both DNA and cell wall of S. flexneri and changed cell morphology and cell membrane permeability. In addition, LED treatment decreased total cell protein concentration of S. flexneri. These results indicated that 405-nm LED treatment effectively controlled S. flexneri contamination of foods and food contact surfaces and that the bacterial inactivation may be the result of damage to multiple cellular components. These findings highlight the potential of LED technology in controlling S. flexneri during food processing, storage, and preparation.

The Antibacterial Activity of Lactic Acid Bacteria from Pickled Spondias dulcis (Ambarella) against Foodborne Pathogens

Pickled fruits are popular condiment not only in Malaysia but in many other countries as well. During the natural pickling process, the lactic acid bacteria are known to be able to produce several antibacterial compounds. The pickled Spondias dulcis or ambarella is among commonly consumed pickled fruit in Malaysia and may be a promising source of lactic acid bacteria. Application of lactic acid bacteria as an alternative to chemical food preservative is believed as natural, safer and sustainable. This study was carried out to isolate and identify lactic acid bacteria from Malaysian local pickled Spondias dulcis and to determine their antibacterial activity against selected Gram-positive and Gram-negative foodborne pathogens. The isolation of lactic acid bacteria was done using a standard method and the isolated colonies with positive preliminary identification based on their morphology on agar, Gram-positive staining characteristic and their negative catalase reaction were chosen for identification with polymerase chain reaction amplification of 16S rRNA gene and sequencing. A total of 2 lactic acid bacteria have been successfully isolated and identified as Lactobacillus fermentum (LABS1) and Enterococcus durans (LABS2). Both isolates were able to demonstrate antibacterial activity against foodborne bacterial pathogens used in this study. This result suggested that the isolated lactic acid bacteria from pickled S. dulcis may have a potential to be applied as natural preservative to control the growth and fight against certain pathogens in food.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Pickled Spondias dulcis is a promising source of lactic acid bacteria having antibacterial activity against foodborne bacterial pathogens&#x0D; Two isolates of LAB identified as Lactobacillus fermentum (LABS1) and Enterococcus durans (LABS2) from pickled Spondias dulcis (ambarella) possessed antibacterial activity against a total of 10 Gram-positive and Gram-negative foodborne pathogens&#x0D; The antibacterial activity using cell free supernatant (CFS) of both LABS1 and LABS2 suggested that they may have potential as natural preservative&#x0D; &#x0D; GRAPHICAL ABSTRACT

Reduced Infection Efficiency of Phage NCTC 12673 on Non-Motile Campylobacter jejuni Strains Is Related to Oxidative Stress.

Campylobacter jejuni is a Gram-negative foodborne pathogen that causes diarrheal disease and is associated with severe post-infectious sequelae. Bacteriophages (phages) are a possible means of reducing Campylobacter colonization in poultry to prevent downstream human infections. However, the factors influencing phage-host interactions must be better understood before this strategy can be predictably employed. Most studies have focused on Campylobacter phage binding to the host surface, with all phages classified as either capsule- or flagella-specific. Here we describe the characterization of a C. jejuni phage that requires functional flagellar glycosylation and motor genes for infection, without needing the flagella for adsorption to the cell surface. Through phage infectivity studies of targeted C. jejuni mutants, transcriptomic analysis of phage-resistant mutants, and genotypic and phenotypic analysis of a spontaneous phage variant capable of simultaneously overcoming flagellar gene dependence and sensitivity to oxidative stress, we have uncovered a link between oxidative stress, flagellar motility, and phage infectivity. Taken together, our results underscore the importance of understanding phage-host interactions beyond the cell surface and point to host oxidative stress state as an important and underappreciated consideration for future phage-host interaction studies.