Attenuation of Multiple Vibrio parahaemolyticus Virulence Factors by Citral

Isolation, characterization, and application of bacteriophage on Vibrio parahaemolyticus biofilm to control seafood contamination

OBJECTIVE

This study intended to isolate a Vibrio-particular phage from the natural environment, analyse its characteristics and genome sequence, and investigate its reduction effect on V. parahaemolyticus biofilm as a biocontrol agent in squid and mackerel.

METHODS

Among 21 phages, phage CAU_VPP01, isolated from beach mud, was chosen for further experiments based on host range and EOP tests. When examining the reduction effect of phage CAU_VPP01 against Vibrio parahaemolyticus biofilms on surfaces (stainless steel [SS] and polyethylene terephthalate [PET]) and food surfaces (squid and mackerel).

RESULTS

The phage showed the most excellent reduction effect at a multiplicity-of-infection (MOI) 10. Three-dimensional images acquired with confocal laser scanning microscopy (CLSM) analysis were quantified using COMSTAT, which showed that biomass, average thickness, and roughness coefficient decreased when treated with the phage. Colour and texture analysis confirmed that the quality of squid and mackerel was maintained after the phage treatment. Finally, a comparison of gene expression levels determined by qRT-PCR analysis showed that the phage treatment induced a decrease in the gene expression of flaA, vp0962, andluxS, as examples.

CONCLUSION

This study indicated that Vibrio-specific phage CAU_VPP01 effectively controlled V. parahaemolyticus biofilms under various conditions and confirmed that the isolated phage could possibly be used as an effective biocontrol weapon in the seafood manufacturing industry.

Revealing the mechanism of citral induced entry of Vibrio vulnificus into viable but not culturable (VBNC) state based on transcriptomics

Citral has attracted much attention as a safe and effective plant-derived bacteriostatic agent. However, the ability of citral to induce the formation of VBNC state in Vibrio vulnificus has not been evaluated. In the present study, V. vulnificus was shown to be induced to form the VBNC state at 4.5 h and 3 h of citral treatment at 4MIC and 6MIC. Moreover, the citral-induced VBNC state of V. vulnificus maintained some respiratory chain activity and was able to recover well in both APW media, APW media supplemented with 5 % (v/v) Tween 80 and 2 mg/mL sodium pyruvate. Field emission and transmission electron microscopy showed that the external structure of the citral-induced VBNC V. vulnificus cells was shortened to short rods, with folded cell membrane, rough cell surface, and dense cytoplasm and loose nuclear material in the internal cell structure. In addition, the possible molecular mechanisms of citral-induced formation and recovery of V. vulnificus in the VBNC state were explored by transcriptomics. Transcriptome analyses revealed that 1118 genes were significantly altered upon entry into the VBNC state, and 1052 genes were changed after resuscitation. Most of the physiological activities related to energy production were inhibited in the citral-induced VBNC state of V. vulnificus; however, the bacteria retained its pathogenicity. The citral-induced resuscitation of V. vulnificus in the VBNC state selectively restored the activity of some genes related to bacterial growth and reproduction. Meanwhile, the expression levels of other genes may have been influenced by citral-induced resuscitation after the formation of the VBNC state. In conclusion, this study evaluated and analyzed the ability and possible mechanism of citral on the formation of VBNC state and the recovery of VBNC state of V. vulnificus, and made a comprehensive assessment for the safety of citral application in food production.

Assessing biofilm formation and resistance of vibrio parahaemolyticus on UV-aged microplastics in aquatic environments

UV degradation of marine microplastics (MPs) could increase their vector potential for pathogenic bacteria and threaten human health. However, little is known about how the degree of UV aging affects interactions between MPs and pathogens and how various types of MPs differ in their impact on seafood safety. This study investigated five types of UV-aged MPs and their impact on Vibrio parahaemolyticus, a seafood pathogen. MPs exposed to UV for 60 days showed similar physicochemical changes such as surface cracking and hydrophobicity reduction. Regardless of the type, longer UV exposure of MPs resulted in more biofilm formation on the surface under the same conditions. V. parahaemolyticus types that formed biofilms on the MP surface showed 1.4- to 5.0-fold upregulation of virulence-related genes compared to those that did not form biofilms, independently of UV exposure. However, longer UV exposure increased resistance of V. parahaemolyticus on MPs to chlorine, heat, and human gastrointestinal environment. This study implies that the more UV degradation occurs on MPs, the more microbial biofilm formation is induced, which can significantly increase virulence and environmental resistance of bacteria regardless of the type of MP.

Bioactive chitosan-citral Schiff base zinc complex: A pH-responsive platform for potential therapeutic applications

The application of CO2 supercritical fluid (SCF) technology has developed rapidly because of its non-toxic, environmentally friendly, mild reaction conditions and safety. The SCF technology can effectively speed up the reaction process of nano-material synthesis, and maintains a high degree of controllability and repeatability. This study mainly included carboxymethyl chitosan sodium salt (CCS), citral (CT), p-coumaric acid (CA), and ZnSO4 as raw materials to prepare CCS-CT-CA-Zn complex as a pH-responsive agent and was investigated using supercritical fluid technique. The coordination structure of Bridge-CCS-CT-CH3COO-CA-Zn-Schiff base/OH and the morphology of the complex agents were verified. The prepared CCS-CT-CA-Zn complex showed good dispersion and uniformity (mean size: 852 ± 202 nm, PdI: 0.301, and mean zeta potential: -31 ± 6 mV). Also, it has a good pH responsive release in an acid environment. Besides, both of CCS-CT-CA-Zn complex (DS-B) and its decomposed mixture in acid (DS-A) demonstrated significant antioxidant and anti-vibrio activity. Moreover, both DS-B complex and DS-A mixture inhibited biofilm formation, swimming, and swarming motilities of V. parahaemolyticus in a dose-dependent manner. This work will provide a scientific basis for the further design and development of natural products derived antibacterial-antioxidant complex agents, food additives and feed additives.

Targeted phytogenic compounds against Vibrio parahaemolyticus biofilms

As one of main culprit of seafood-associated human illness, Vibrio parahaemolyticus can readily accumulate on biotic or abiotic surfaces to form biofilms in the seafood processing environment. Biofilm formation on various surfaces can provide a protective barrier for viable bacterial cells that are resistant to most traditional bacteriostatic measures. This underscores the necessity and urgency of developing effective alternative strategies to control V. parahaemolyticus biofilms. Plants have always provided an extensive and infinite source of biologically active compounds for "green" antibiofilm agents. This review summarizes recent developments in promising multitargeted phytogenic compounds against V. parahaemolyticus biofilms. This review provides valuable insights into potential research targets that can be pursued further to identify potent natural antibiofilm agents in the food industry.

Anti-Vibrio parahaemolyticus compounds from Streptomyces parvus based on Pan-genome and subtractive proteomics

Introduction

Vibrio parahaemolyticus is a foodborne pathogen commonly found in seafood, and drug resistance poses significant challenges to its control. This study aimed to identify novel drug targets for antibacterial drug discovery.

Methods

To identify drug targets, we performed a pan-genome analysis on 58 strains of V. parahaemolyticus genomes to obtain core genes. Subsequently, subtractive proteomics and physiochemical checks were conducted on the core proteins to identify potential therapeutic targets. Molecular docking was then employed to screen for anti-V. parahaemolyticus compounds using a in-house compound library of Streptomyces parvus, chosen based on binding energy. The anti-V. parahaemolyticus efficacy of the identified compounds was further validated through a series of experimental tests.

Results and Discussion

Pangenome analysis of 58 V. parahaemolyticus genomes revealed that there were 1,392 core genes. After Subtractive proteomics and physiochemical checks, Flagellar motor switch protein FliN was selected as a therapeutic target against V. parahaemolyticus. FliN was modeled and docked with Streptomyces parvus source compounds, and Actinomycin D was identified as a potential anti-V. parahaemolyticus agent with a strong binding energy. Experimental verification confirmed its effectiveness in killing V. parahaemolyticus and significantly inhibiting biofilm formation and motility. This study is the first to use pan-genome and subtractive proteomics to identify new antimicrobial targets for V. parahaemolyticus and to identify the anti-V. parahaemolyticus effect of Actinomycin D. These findings suggest potential avenues for the development of new antibacterial drugs to control V. parahaemolyticus infections.

Citral and trans-cinnamaldehyde, two plant-derived antimicrobial agents can induce Staphylococcus aureus into VBNC state with different characteristics

Viable but nonculturable (VBNC) state bacteria are difficult to detect in the food industry due to their nonculturable nature and their recovery characteristics pose a potential threat to human health. The results of this study indicated that S. aureus was found to enter the VBNC state completely after induced by citral (1 and 2 mg/mL) for 2 h, and after induced by trans-cinnamaldehyde (0.5 and 1 mg/mL) for 1 h and 3 h, respectively. Except for VBNC state cells induced by 2 mg/mL citral, the VBNC state cells induced by the other three conditions (1 mg/mL citral, 0.5 and 1 mg/mL trans-cinnamaldehyde) were able to be resuscitated in TSB media. In the VBNC state cells induced by citral and trans-cinnamaldehyde, the ATP concentration was reduced, the hemolysin-producing ability was significantly decreased, but the intracellular ROS level was elevated. The results of heat and simulated gastric fluid experiments showed different environment resistance on VBNC state cells induced by citral and trans-cinnamaldehyde. In addition, by observing the VBNC state cells showed that irregular folds on the surface, increased electron density inside and vacuoles in the nuclear region. What's more, S. aureus was found to enter the VBNC state completely after induced by meat-based broth containing citral (1 and 2 mg/mL) for 7 h and 5 h, after induced by meat-based broth containing trans-cinnamaldehyde (0.5 and 1 mg/mL) for 8 h and 7 h. In summary, citral and trans-cinnamaldehyde can induce S. aureus into VBNC state and food industry needs to comprehensively evaluate the antibacterial capacity of these two plant-derived antimicrobial agents.

Transcriptomic analyses reveal the potential antibacterial mechanism of citral against Staphylococcus aureus

Background

The emergence of multi-drug resistant Staphylococcus aureus (S. aureus) has posed a challenging clinical problem for treating its infection. The development of novel or new antibacterial agents becomes one of the useful methods to solve this problem, and has received more attention over the past decade. Citral is reported to have antibacterial activity against S. aureus, but its mechanism is yet entirely clear.

Methods

To reveal the antibacterial mechanism of citral against S. aureus, comparative transcriptomic analysis was carried out to analyze the gene expression differences between the citral-treated and untreated groups. The changes of protein, adenosine triphosphate (ATP) and reactive oxygen species (ROS) content in S. aureus caused by citral were also examined.

Results

Six hundred and fifty-nine differentially expressed genes were obtained according to the comparative transcriptomic analysis, including 287 up-regulated genes and 372 down-regulated genes. The oxidoreductase activity and fatty acid degradation pathway were enriched in up-regulated genes, and ribosome and S. aureus infection pathway were enriched in down-regulated genes. Meanwhile, physiological trials revealed a decline in ATP and protein levels, but an increase in ROS content within the citral-treated group. Thus, it can be inferred that the antibacterial effects of citral against S. aureus were likely due to its ability to decrease ATP content by down-regulating ATP synthase genes (atpD and atpG), reduce protein content, induce cell membrane and cell wall damages, accumulate ROS, and down-regulate virulence factor genes to reduce pathogenicity.

Conclusion

These findings revealed the antibacterial mechanism of citral was likely a type of multi-target mode that affected multiple molecular processes in S. aureus, which lays the groundwork for further exploitation of citral as a therapeutic candidate against S. aureus infections.

Characterization and antivibrio activity of chitosan-citral Schiff base calcium complex for a calcium citrate sustained release antibacterial agent

Vibrio parahemolyticus is the "Number one killer" of seafood products. Anti-vibrio agents having low cost and high-safety are urgently needed to supplement the application needs. This work attempted to prepare CS-CT-CCa complex with citral (CT), chitosan (CS) and calcium citrate (CCa) as raw material by microwave-assisted high-pressure homogenization. Additionally the coordination structure and morphology of Bridge-CS-CT-Schiff base/OH-CCa were verified. The prepared CS-CT-CCa had a well-dispersed property (the size: 3.55~9.33 μm and the zeta potential: +38.7~+67.5 mV) and an excellent sustained released ability (sustained release up to 180 min). MIC, Glucose assay, MDA assay, biofilm formation inhibition assay, SEM, swimming and swarming motility assay demonstrated that CS-CT-CCa had strong (MIC of 128 μg/ml) and sustained (more than 12 h) inhibitory effects against V. parahaemolyticus. Meanwhile, CS-CT-CCa could increase the membrane permeability of V. parahaemolyticus and inhibit their biofilm-forming ability in a dose-dependent manner. It could be inferred that the antibacterial activities against V. parahaemolyticus caused inhibition of biofilm formation, swimming and swarming motilities. This study provided necessary data for the further design and development of chitosan antibacterial agents, food and feed additives.

Enhancing the AI-2/LuxS quorum sensing system in Lactiplantibacillus plantarum: Effect on the elimination of biofilms grown on seafoods

The biofilm clustered with putrefying microorganisms and seafood pathogens could cover the surface of aquatic products that pose a risk to cross-contaminating food products or even human health. Fighting biofilms triggers synchronous communication associated with microbial consortia to regulate their developmental processes, and the enhancement of the quorum sensing system in Lactiplantibacillus plantarum can serve as an updated starting point for antibiofilm-forming strategies. Our results showed that the exogenous 25 mM L-cysteine induced a significant strengthening in the AI-2/LuxS system of Lactiplantibacillus plantarum SS-128 along with a stronger bacteriostatic ability, resulting in an effective inhibition of biofilms formed by the simplified microbial consortia constructed by Vibrio parahaemolyticus and Shewanella putrefaciens grown on shrimp and squid surfaces. The accumulation of AI-2 allowed the suppression of the expression of biofilm-related genes in V. parahaemolyticus under the premise of L. plantarum SS-128 treatment, contributing to the inhibition effect. In addition, strengthening the AI-2/LuxS system is also conducive to eliminating preexisting biofilms by L. plantarum SS-128. This study suggests that the enhancement of the AI-2/LuxS system of lactic acid bacteria enables the regulation of interspecific communication within biofilms to be a viable tool to efficiently reduce and eradicate potentially harmful biofilms from aquatic product sources, opening new horizons for combating biofilms.

Antibiofilm effect and mechanism of protocatechuic aldehyde against Vibrio parahaemolyticus

This study investigated the effect of protocatechuic aldehyde (PCA) on Vibrio parahaemolyticus biofilm formation and its effects on gene expression. Crystal violet assay, metabolic activity assay, and fluorescence experiments were used to evaluate the antibiofilm activities of PCA and to reveal its possible antibiofilm mechanisms using transcriptomic analysis. The results indicated that the minimum antibacterial concentration of PCA against V. parahaemolyticus was 300 μg/mL. PCA (9.375 μg/mL) inhibited biofilm generation and adhesion of the mature biofilm. PCA (75 μg/mL) significantly reduced the metabolic viability of V. parahaemolyticus, reduced polysaccharide production, and inhibited cell surface flagella-mediated swimming and aggregation phenotypes. Meanwhile, transcriptome analysis showed that the key genes of V. parahaemolyticus expressed under PCA (75 μg/mL) inhibition were mainly related to biofilm formation (pfkA, galE, narL, and oppA), polysaccharide production and adhesion (IF, fbpA, and yxeM), and motility (cheY, flrC, and fliA). By regulating these key genes, PCA reduced biofilm formation, suppressed polysaccharide production and transport, and prevented the adhesion of V. parahaemolyticus, thereby reducing the virulence of V. parahaemolyticus. This study demonstrated that protocatechuic aldehyde can be used to control V. parahaemolyticus biofilm to ensure food safety.

Propionate and Butyrate Inhibit Biofilm Formation of Salmonella Typhimurium Grown in Laboratory Media and Food Models

Salmonella is among the most frequently isolated foodborne pathogens, and biofilm formed by Salmonella poses a potential threat to food safety. Short-chain fatty acids (SCFAs), especially propionate and butyrate, have been demonstrated to exhibit a beneficial effect on promoting intestinal health and regulating the host immune system, but their anti-biofilm property has not been well studied. This study aims to investigate the effects of propionate or butyrate on the biofilm formation and certain virulence traits of Salmonella. We investigated the effect of propionate or butyrate on the biofilm formation of Salmonella enterica serovar Typhimurium (S. Typhimurium) SL1344 grown in LB broth or food models (milk or chicken juice) by crystal violet staining methods. Biofilm formation was significantly reduced in LB broth and food models and the reduction was visualized using a scanning electron microscope (SEM). Biofilm metabolic activity was attenuated in the presence of propionate or butyrate. Meanwhile, both SCFAs decreased AI-2 quorum sensing based on reporter strain assay. Butyrate, not propionate, could effectively reduce bacterial motility. Bacterial adhesion to and invasion of Caco-2 cells were also significantly inhibited in the presence of both SCFAs. Finally, two SCFAs downregulated virulence genes related to biofilm formation and invasion through real-time polymerase chain reaction (RT-PCR). These findings demonstrate the potential application of SCFAs in the mitigation of Salmonella biofilm in food systems, but future research mimicking food environments encountered during the food chain is necessitated.

Antibiofilm Efficacy of Quercetin against Vibrio parahaemolyticus Biofilm on Food-Contact Surfaces in the Food Industry

Vibrio parahaemolyticus, one of the most common foodborne pathogenic bacteria that forms biofilms, is a persistent source of concern for the food industry. The food production chain employs a variety of methods to control biofilms, although none are completely successful. This study aims to evaluate the effectiveness of quercetin as a food additive in reducing V. parahaemolyticus biofilm formation on stainless-steel coupons (SS) and hand gloves (HG) as well as testing its antimicrobial activities. With a minimum inhibitory concentration (MIC) of 220 µg/mL, the tested quercetin exhibited the lowest bactericidal action without visible growth. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin at sub-MICs levels (1/2, 1/4, and 1/8 MIC) against V. parahaemolyticus was examined. Control group was not added with quercetin. With increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of target genes linked to flagellar motility (flaA, flgL), biofilm formation (vp0952, vp0962), virulence (VopQ, vp0450), and quorum-sensing (aphA, luxS) were all dramatically suppressed. Quercetin (0−110 μg/mL) was investigated on SS and HG surfaces, the inhibitory effect were 0.10−2.17 and 0.26−2.31 log CFU/cm2, respectively (p < 0.05). Field emission scanning electron microscopy (FE-SEM) corroborated the findings because quercetin prevented the development of biofilms by severing cell-to-cell contacts and inducing cell lysis, which resulted in the loss of normal cell shape. Additionally, there was a significant difference between the treated and control groups in terms of motility (swimming and swarming). According to our research, quercetin produced from plants should be employed as an antibiofilm agent in the food sector to prevent the growth of V. parahaemolyticus biofilms. These results indicate that throughout the entire food production chain, bacterial targets are of interest for biofilm reduction with alternative natural food agents in the seafood industry.

Antimicrobial Efficacy of Quercetin against Vibrio parahaemolyticus Biofilm on Food Surfaces and Downregulation of Virulence Genes

For the seafood industry, Vibrio parahaemolyticus, one of the most prevalent food-borne pathogenic bacteria that forms biofilms, is a constant cause of concern. There are numerous techniques used throughout the food supply chain to manage biofilms, but none are entirely effective. Through assessing its antioxidant and antibacterial properties, quercetin will be evaluated for its ability to prevent the growth of V. parahaemolyticus biofilm on shrimp and crab shell surfaces. With a minimum inhibitory concentration (MIC) of 220 µg/mL, the tested quercetin exhibited the lowest bactericidal action without visible growth of bacteria. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin without (control) and with sub-MICs levels (1/2, 1/4, and 1/8 MIC) against V. parahaemolyticus was examined. With increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of related genes linked to flagella motility (flaA and flgL), biofilm formation (vp0952 and vp0962), and quorum-sensing (luxS and aphA) were all dramatically reduced (p < 0.05). Quercetin (0−110 μg/mL) was investigated on shrimp and crab shell surfaces, the inhibitory effects were 0.68−3.70 and 0.74−3.09 log CFU/cm2, respectively (p < 0.05). The findings were verified using field emission scanning electron microscopy (FE-SEM), which revealed quercetin prevented the development of biofilms by severing cell-to-cell contacts and induced cell lysis, which resulted in the loss of normal cell shape. Furthermore, there was a substantial difference in motility between the treatment and control groups (swimming and swarming). According to our findings, plant-derived quercetin should be used as an antimicrobial agent in the food industry to inhibit the establishment of V. parahaemolyticus biofilms. These findings suggest that bacterial targets are of interest for biofilm reduction with alternative natural food agents in the seafood sector along the entire food production chain.

Antibiofilm and Antiquorum Sensing Potential of Lactiplantibacillus plantarum Z057 against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a widespread foodborne pathogen that causes serious seafood-borne gastrointestinal infections. Biofilm and quorum sensing (QS) are critical in regulating these infections. In this study, first, the ability of Lactiplantibacillus plantarum Z057 to compete, exclude, and displace V. parahaemolyticus biofilm was evaluated. Then, the inhibitory effects of L. plantarum Z057 extract (Z057-E) on V. parahaemolyticus biofilm and QS were explored from the aspects of biofilm biomass, metabolic activity, physicochemical properties, extracellular polymer matrix content, QS signal AI-2 activity, biofilm microstructure, and the expression levels of biofilm and QS-related genes. Results showed that L. plantarum Z057 effectively inhibited biofilm formation of V. parahaemolyticus and interfered with the adhesion of V. parahaemolyticus on the carrier surface. In addition, the Z057-E could significantly reduce the biofilm biomass, metabolic activity, hydrophobicity, auto-aggregation ability, swimming and swarming migration diameter, AI-2 activity, extracellular polysaccharide (EPS), and extracellular protein content of V. parahaemolyticus. Fluorescence microscope and scanning electron microscope (SEM) images demonstrated that the Z057-E could efficiently inactivate the living cells, destroy the dense and complete biofilm architectures, and reduce the essential component of the extracellular polymer matrix. Real-time fluorescence quantitative PCR revealed that the Z057-E treatment down-regulated the expression of flagellum synthesis-related genes (flaA, flgM), EPS, and extracellular protein synthesis-related genes (cpsA, cpsQ, cpsR, ompW), QS-related genes (luxS, aphA, opaR), and hemolysin secretion-related genes (toxS, toxR) of V. parahaemolyticus. Thus, our results suggested that L. plantarum Z057 could represent an alternative biocontrol strategy against foodborne pathogens with anti-adhesive, antibiofilm, and antiquorum sensing activities.

Microbiological assessment of marine and estuarine ecosystems using fecal indicator bacteria, Salmonella, Vibrio and antibiotic resistance pattern

Marine and estuarine environments are often affected by microbiological contamination that adversely affects their use and severely impacts human health. To examine the influence of anthropogenic activities, this study used two different ecosystems in Agadir Bay, to compare fecal indicator bacteria (FIB) and bacterial pathogen profiles over two years. Vibrio target pathogens were detected at a high frequency (49.3%), while a low percentage (5.5%) was noted for Salmonella. Apart from those mentioned above, several other pathogenic bacteria were detected such as Cronobacter sakzakii, Pseudomonas fluorescens, and Aeromonas hydrophila. We also investigated the antimicrobial resistance of the pathogenic bacteria isolated. Salmonella strains were sensitive to all the antibiotics used, except ampicillin, amoxicillin + Ac clavulanic and chloramphenicol. And Vibrio strains were resistant to ampicillin, cephalothin, amikacin, and ciprofloxacin. This study highlights the limitations of FIB in assessing the microbiological quality and the importance of environmental surveys in understanding the distribution of pathogens.

Antagonistic activity and mode of action of trypacidin from marine-derived Aspergillus fumigatus against Vibrio parahaemolyticus

This study aimed to investigate the antagonistic activity and mode of action of trypacidin from marine-derived Aspergillus fumigatus against Vibrio parahaemolyticus. Results indicated that the minimal inhibitory concentration and minimal bactericidal concentration of trypacidin against V. parahaemolyticus were 31.25 and 62.5 μg/mL, respectively, which was better than that of streptomycin sulfate. Trypacidin remarkably inhibited the growth of V. parahaemolyticus and had a strong destructive effect on cell wall permeability and integrity, cell membrane permeability, and morphological alterations. Its potential as an antibacterial agent for aquatic products must be further explored.

Vanillic acid combats Vibrio alginolyticus by cell membrane damage and biofilm reduction

Antibiotics are the most powerful weapon against bacterial infectious diseases in aquaculture. However, the indiscriminate usage of antibiotics often culminates in the emerging development of antibiotic-resistant bacteria, making it imperative to search for novel types of antimicrobial agents. This study investigated the antibacterial and antivirulence effects of vanillic acid (VA) against the fish pathogen, Vibrio alginolyticus. We showed that VA had a good anti-Vibrio activity with minimal inhibitory concentration (MIC) of 1.0 mg/ml. In addition, VA wielded its antibacterial action in a dose-/time-dependent manner by causing cell membrane damage and increasing membrane permeability, which is evidenced by increasing the conductivity and malondialdehyde content in the treated cell cultures and the scanning electron microscopy images. Furthermore, VA significantly reduced the biofilm-forming capability, mobility and exotoxin production (protease and exopolysaccharide) and downregulation of the expression of biofilm- and virulence-associated genes (sypG, fliS, fliK, lafA, lafK, asp and luxR) was seen in the V. alginolyticus that exposed to VA at subinhibitory concentrations. Overall, our findings suggested that VA may be of interest for treating V. alginolyticus-associated infections in aquaculture.

New Trends in Photodynamic Inactivation (PDI) Combating Biofilms in the Food Industry-A Review

Biofilms cause problems in the food industry due to their persistence and incompetent hygiene processing technologies. Interest in photodynamic inactivation (PDI) for combating biofilms has increased in recent years. This technique can induce microbial cell death, reduce cell attachment, ruin biofilm biomolecules and eradicate structured biofilms without inducing microbial resistance. This review addresses microbial challenges posed by biofilms in food environments and highlights the advantages of PDI in preventing and eradicating microbial biofilm communities. Current findings of the antibiofilm efficiencies of this technique are summarized. Additionally, emphasis is given to its potential mechanisms and factors capable of influencing biofilm communities, as well as promising hurdle strategies.

Prevalence, detection of virulence genes and antimicrobial susceptibility of pathogen Vibrio species isolated from different types of seafood samples at "La Nueva Viga" market in Mexico City

Some Vibrio species are important human pathogens owing to they cause infectious diseases such as gastroenteritis, wound infections, septicemia or even death. Many of these illnesses are associated with consumption of contaminated seafood. In the present study, we evaluated the presence of pathogenic Vibrio species, their virulence and antimicrobial susceptibility from 285 different kind of seafood samples from "La Nueva Viga" market in Mexico City. The PCR assay was used for amplification the vppC (collagenase), vmh (hemolysin), tlh (thermolabile hemolysin), and vvhA (hemolytic cytolysin) genes that are specific to Vibrio alginolyticus (detected in 27%), Vibrio mimicus (23.2%), Vibrio parahaemolyticus (28.8%) and Vibrio vulnificus (21.1%), respectively. Several genes encoding virulence factors were amplified. These included V. alginolyticus: pvuA (17.9%), pvsA (50%), wza and lafA (100%); V. mimicus: iut A (60%), toxR (100%); V. parahaemolyticus: pvuA (58.7%), pvsA (26.1%), wza (2.2%), and lafA (100%); and V. vulnificus: wcrA (77.5%), gmhD (57.5%), lafA (100%) and motA (30%). The antibiotic susceptibility of the Vibrio species isolates revealed that most of them were resistant to ampicillin, cephalothin and carbenicillin but susceptible to pefloxacin and trimethoprim-sulfamethoxazole. Our results indicated a high prevalence of pathogenic Vibrio species in seafood, a high presence of virulence genes and that Vibrio species continuously exposed to antibiotics, therefore, consumption of these kind of seafood carries a potential risk for foodborne illness.

Negative Impact of Citral on Susceptibility of Pseudomonas aeruginosa to Antibiotics

Essential oils (EOs) or their components are widely used by inhalation or nebulization to fight mild respiratory bacterial infections. However, their interaction with antibiotics is poorly known. In this study we evaluated the effects of citral, the main component of lemongrass oil, on in vitro susceptibility of Pseudomonas aeruginosa to antibiotics. Exposure of strain PA14 to subinhibitory concentrations of citral increased expression of operons encoding the multidrug efflux systems MexEF-OprN and MexXY/OprM, and bacterial resistance to anti-pseudomonal antibiotics including imipenem (twofold), gentamicin (eightfold), tobramycin (eightfold), ciprofloxacin (twofold), and colistin (≥128-fold). Use of pump deletion mutants showed that in addition to efflux other mechanisms were involved in this citral-induced phenotype. Determination of Zeta potential suggested that citral impairs the cell surface binding of aminoglycosides and colistin used at low concentrations (≤10 μg/mL). Moreover, experiments based on Raman spectroscopy and high-resolution mass spectrometry demonstrated formation of a Schiff base between the aldehyde group of citral and amino-groups of tobramycin and colistin. Chemical synthesis of tobracitryl, the imine compound resulting from condensation of citral and tobramycin, confirmed the loss of antibiotic activity due to adduct formation. Altogether these data point to the potential risk concern of self-medication with EOs containing citral in patients suffering from P. aeruginosa chronic lung infections and being treated with aerosols of aminoglycoside or colistin.

Proteomic and Systematic Functional Profiling Unveils Citral Targeting Antibiotic Resistance, Antioxidant Defense, and Biofilm-Associated Two-Component Systems of Acinetobacter baumannii To Encumber Biofilm and Virulence Traits

Acinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Acinetobacter baumannii has been reported as a multidrug-resistant bacterium due to biofilms and antimicrobial resistance mechanisms. Hence, novel therapeutic strategies are necessary to overcome A. baumannii infections. This study revealed that citral at 200 μg/ml attenuated A. baumannii biofilms by up to 90% without affecting viability. Furthermore, microscopic analyses and in vitro assays confirmed the antibiofilm efficacy of citral. The global effect of citral on A. baumannii was evaluated by proteomic, transcriptional, and in silico approaches. Two-dimensional (2D) gel electrophoresis and matrix-assisted laser desorption ionization–time of flight/time of flight (MALDI-TOF/TOF) analyses were used to assess the effect of citral on the A. baumannii cellular proteome. Quantitative real-time PCR (qPCR) analysis was done to validate the proteomic data and identify the differentially expressed A. baumannii genes. Protein-protein interactions, gene enrichment, and comparative gene network analyses were performed to explore the interactions and functional attributes of differentially expressed proteins of A. baumannii. Global omics-based analyses revealed that citral targeted various mechanisms such as biofilm formation, antibiotic resistance, antioxidant defense, iron acquisition, and type II and type IV secretion systems. The results of antioxidant analyses and antibiotic sensitivity, blood survival, lipase, and hemolysis assays validated the proteomic results. Cytotoxicity analysis showed a nontoxic effect of citral on peripheral blood mononuclear cells (PBMCs). Overall, the current study unveiled that citral has multitarget efficacy to inhibit the biofilm formation and virulence of A. baumannii.

IMPORTANCEAcinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Motility of Vibrio spp.: regulation and controlling strategies

Flagellar motility in bacteria is a highly regulated and complex cellular process that requires high energy investment for movement and host colonization. Motility plays an important role in the lifestyle of Vibrio spp. in the aquatic environment and during host colonization. Flagellar motility in vibrios is associated with several cellular processes, such as movement, colonization, adhesion, biofilm formation, and virulence. The transcription of all flagella-related genes occurs hierarchically and is regulated positively or negatively by several transcription factors and regulatory proteins. The flagellar regulatory hierarchy is well studied in Vibrio cholerae and Vibrio parahaemolyticus. Here, we compared the regulatory cascade and molecules involved in the flagellar motility of V. cholerae and V. parahaemolyticus in detail. The evolutionary relatedness of the master regulator of the polar and lateral flagella in different Vibrio species is also discussed. Although they can form symbiotic associations of some Vibrio species with humans and aquatic organisms can be harmed by several species of Vibrio as a result of surface contact, characterized by flagellar movement. Thus, targeting flagellar motility in pathogenic Vibrio species is considered a promising approach to control Vibrio infections. This approach, along with the strategies for controlling flagellar motility in different species of Vibrio using naturally derived and chemically synthesized compounds, is discussed in this review. KEY POINTS: • Vibrio species are ubiquitous and distributed across the aquatic environments. • The flagellar motility is responsible for the chemotactic movement and initial colonization to the host. • The transition from the motile into the biofilm stage is one of the crucial events in the infection. • Several signaling pathways are involved in the motility and formation of biofilm. • Attenuation of motility by naturally derived or chemically synthesized compounds could be a potential treatment for preventing Vibrio biofilm-associated infections.

Lemon Grass Essential Oil Does not Modulate Cancer Cells Multidrug Resistance by Citral-Its Dominant and Strongly Antimicrobial Compound

With strong antimicrobial properties, citral has been repeatedly reported to be the dominant component of lemongrass essential oil. Here, we report on a comparison of the antimicrobial and anticancer activity of citral and lemongrass essential oil. The lemongrass essential oil was prepared by the vacuum distillation of fresh Cymbopogon leaves, with a yield of 0.5% (w/w). Citral content was measured by gas chromatography/high-resolution mass spectrometry (GC-HRMS) and determined to be 63%. Antimicrobial activity was tested by the broth dilution method, showing strong activity against all tested bacteria and fungi. Citral was up to 100 times more active than the lemongrass essential oil. Similarly, both citral and essential oils inhibited bacterial communication and adhesion during P. aeruginosa and S. aureus biofilm formation; however, the biofilm prevention activity of citral was significantly higher. Both the essential oil and citral disrupted the maturated P. aeruginosa biofilm with the IC₅₀ 7.3 ± 0.4 and 0.1 ± 0.01 mL/L, respectively. Although it may seem that the citral is the main biologically active compound of lemongrass essential oil and the accompanying components have instead antagonistic effects, we determined that the lemongrass essential oil-sensitized methicillin-resistant S. aureus (MRSA) and doxorubicin-resistant ovarian carcinoma cells and that this activity was not caused by citral. A 1 mL/L dose of oil-sensitized MRSA to methicillin up to 9.6 times and a dose of 10 µL/L-sensitized ovarian carcinoma to doxorubicin up to 1.8 times. The mode of multidrug resistance modulation could be due to P-glycoprotein efflux pump inhibition. Therefore, the natural mixture of compounds present in the lemongrass essential oil provides beneficial effects and its direct use may be preferred to its use as a template for citral isolation.

Targets and pathways involved in the antitumor activity of citral and its stereo-isomers

This review provides a comprehensive analysis of the anticancer potential of the natural product citral (CIT) found in many plants and essential oils, and extensively used in the food and cosmetic industry. CIT is composed of two stereoisomers, the trans-isomer geranial being a more potent anticancer compound than the cis-isomer neral. CIT inhibits cancer cell proliferation and induces cancer cell apoptosis. Its pluri-factorial mechanism of anticancer activity is essentially based on three pillars: (i) a drug-induced accumulation of reactive oxygen species in cancer cells leading to an oxidative burst and DNA damages, (ii) a colchicine-like inhibition of tubulin polymerization and promotion of microtubule depolymerization, associated with an inhibition of the microtubule affinity-regulating kinase MARK4, and (iii) a potent inhibition of the aldehyde dehydrogenase isoform ALDH1A3 which is associated with cancer stem cell proliferation and chemoresistance. This unique combination of targets and pathways confers a significant anticancer potential. However, the intrinsic potency of CIT is limited, mainly because the drug is not very stable and has a low bioavailability and it does not present a high selectivity for cancer cells versus non-tumor cells. Stable formulations of CIT, using cyclodextrins, biodegradable polymers, or various nano-structured particles have been designed to enhance the bioavailability, to increase the effective doses window and to promote the anticancer activity. The lack of tumor cell selectivity is more problematic and limits the use of the drug in cancer therapy. Nevertheless, CIT offers interesting perspectives to design more potent analogues and drug combinations with a reinforced antitumor potential.

Prevalence and antibiotic resistance patterns of Vibrio parahaemolyticus isolated from different types of seafood in Selangor, Malaysia

Vibrio parahaemolyticus is a foodborne bacterial pathogen that may cause gastroenteritis in humans through the consumption of seafood contaminated with this microorganism. The emergence of antimicrobial and multidrug-resistant bacteria is another serious public health threat worldwide. In this study, the prevalence and antibiotic susceptibility test of V. parahaemolyticus in blood clams, shrimps, surf clams, and squids were determined. The overall prevalence of V. parahaemolyticus in seafood was 85.71% (120/140), consisting of 91.43% (32/35) in blood clam, 88.57% (31/35) in shrimps, 82.86% (29/35) in surf clams, and 80% (28/35) in squids. The majority of V. parahaemolyticus isolates from the seafood samples were found to be susceptible to most antibiotics except ampicillin, cefazolin, and penicillin. The MAR indices of V. parahaemolyticus isolates ranged from 0.04 to 0.71 and about 90.83% of isolates were found resistant to more than one antibiotic. The high prevalence of V. parahaemolyticus in seafood and multidrug-resistant isolates detected in this study could pose a potential risk to human health and hence appropriate control methods should be in place to minimize the potential contamination and prevent the emergence of antibiotic resistance.

Heat-Assisted Pulsed Electric Field Treatment for the Inactivation of Saccharomyces cerevisiae: Effects of the Presence of Citral

Pulsed electric field (PEF) treatment is a non-thermal technology that has shown good potential for microbial inactivation. However, in many cases, it cannot be sufficient to avoid microbial proliferation, and the combination with other stabilizing technologies is needed. In the framework of the hurdle concept, several researches have been focused on the use of PEF in combination with heat and/or antimicrobials to increase its efficacy. This study investigated the inactivation effect of PEF on a strain of Saccharomyces cerevisiae (isolated from spoiled beverages) in a model system (growth medium). The efficacy of PEF treatment was evaluated in relation to different variables, such as electric field strength (25 and 50 kV/cm), treatment time (from 1 to 5 s), initial inoculum level (4 or 6 log cfu/ml), preheating at 50°C, medium pH (4 or 6), and addition of citral at sublethal concentration (i.e., half of minimum inhibiting concentration). The data from plate counting, modeled with the Weibull equation, showed that one of the main factors affecting yeast inactivation was the preheating of the suspension at 50°C. Indeed, higher cell load reductions were obtained with heat-assisted PEF, especially in the presence of citral. The effect of initial cell load was negligible, while pH affected yeast inactivation only without preheating, with higher death kinetics at pH 6. Flow cytometry (FCM) analysis confirmed higher mortality under these conditions. However, the occurrence of injured cells, especially in samples treated at pH 4, was observed. The ability of these cells to recover from the damages induced by treatments was affected by both citral and preheating. The synergic effects of PEF, preheating, and citral were likely due to the increase of membrane permeability (especially at pH 6), as the primary target of electroporation, which favored the solubilization of citral in the cell membrane, enhancing the efficacy of the whole process. The multi-analytical approach (traditional plate counting and FCM) allowed defining parameters to increase PEF efficacy against S. cerevisiae. Moreover, FCM, able to discriminate different physiological states of the yeast population, was helpful to better clarify the action mechanism and the potential recovery of cells after treatment.