Antibacterial and antibiofilm activity of coenzyme Q0 against Vibrio parahaemolyticus

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.

The role of rcpA gene in regulating biofilm formation and virulence in Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a common seafood-borne pathogen that can colonize the intestine of host and cause gastroenteritis. Biofilm formation by V. parahaemolyticus enhances its persistence in various environments, which poses a series of threats to food safety. This work aims to investigate the function of rcpA gene in biofilm formation and virulence of V. parahaemolyticus. Deletion of rcpA significantly reduced motility, biofilm biomass, and extracellular polymeric substances, and inhibited biofilm formation on a variety of food and food contact surfaces. In mice infection model, mice infected with ∆rcpA strain exhibited a decreased rate of pathogen colonization, a lower level of inflammatory cytokines, and less tissue damage when compared to mice infected with wild type strain. RNA-seq analysis revealed that 374 genes were differentially expressed in the rcpA deletion mutant, which include genes related to quorum sensing, flagellar system, ribosome, type VI secretion system, biotin metabolism and transcriptional regulation. In conclusion, rcpA plays a role in determining biofilm formation and virulence of V. parahaemolyticus and further research is necessitated to fully understand its function in V. parahaemolyticus.

Antimicrobial Activity of Eugenol Against Bacillus cereus and Its Application in Skim Milk

Bacillus cereus is a foodborne pathogen widely distributed in the large-scale catering industry and produces spores. The study explored the antibacterial activity, potential mechanism of eugenol against B. cereus, and spores with germination rate. The minimum inhibitory concentration (MIC; 0.6 mg/mL) of eugenol to six B. cereus strains was compared with the control; B. cereus treated with eugenol had a longer lag phase. Eugenol at a concentration of more than 1/2MIC decreased viable B. cereus (∼5.7 log colony-forming unit [CFU]/mL) counts below detectable limits within 2 h, and eugenol of 3MIC reduced B. cereus (∼5.9 log CFU/mL) in skim milk below detectable limits within 30 min. The pH values of skim milk were unaffected by the addition of eugenol. The ΔE values below 2 show that the color variations of skim milk were not visible to the human eye. For sensory evaluation, eugenol did not significantly affect the color or structural integrity of the skim milk. It had a negative impact on the flavor and general sensory acceptance of the treated milk. Eugenol hyperpolarized B. cereus cell membrane, decreased intracellular ATP concentration, and increased intracellular reactive oxygen species contents and extracellular malondialdehyde contents, resulting in the cell membrane of B. cereus being damaged and permeabilized, and cell morphology being changed. In addition, according to the viable count, confocal laser scanning microscopy, and spore morphology changes, eugenol reduced the germination rate of B. cereus spores. These findings suggest that eugenol can be used as a new natural antibacterial agent to control B. cereus and spores in the food production chain.

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-Biofilm Activity of Laurel Essential Oil against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a primary seafood-associated pathogen that could cause gastroenteritis. It can attach to various surfaces and form a biofilm, which poses serious threats to food safety. Hence, an effective strategy is urgently needed to control the biofilm formation of V. parahaemolyticus. Laurel essential oil (LEO) is used in food, pharmaceutical and other industries, and is commonly used as a flavoring agent and valuable spice in food industries. The potential antibiofilm effects of LEO against V. parahaemolyticus were examined in this study. LEO obviously reduced biofilm biomass at subinhibitory concentrations (SICs). It decreased the metabolic activity and viability of biofilm cells. Microscopic images and Raman spectrum indicted that LEO interfered with the structure and biochemical compositions of biofilms. Moreover, it also impaired swimming motility, decreased hydrophobicity, inhibited auto-aggregation and reduced attachment to different food-contact surfaces. RT-qPCR revealed that LEO significantly downregulated transcription levels of biofilm-associated genes of V. parahaemolyticus. These findings demonstrate that LEO could be potentially developed as an antibiofilm strategy to control V. parahaemolyticus biofilms in food industries.

Inhibition of Cronobacter sakazakii Biofilm Formation and Expression of Virulence Factors by Coenzyme Q0

In this study, we investigated the inhibitory effects of coenzyme Q0 (CoQ0) on biofilm formation and the expression of virulence genes by Cronobacter sakazakii. We found that the minimum inhibitory concentration of CoQ0 against C. sakazakii strains ATCC29544 and ATCC29004 was 100 μg/mL, while growth curve assays showed that subinhibitory concentrations (SICs) of CoQ0 for both strains were 6.4, 3.2, 1.6 and 0.8 μg/mL. Assays exploring the inhibition of specific biofilm formation showed that SICs of CoQ0 inhibited biofilm formation by C. sakazakii in a dose-dependent manner, which was confirmed by scanning electron microscopy and confocal laser scanning microscopy analyses. CoQ0 inhibited the swimming and swarming motility of C. sakazakii and reduced its ability to adhere to and invade HT-29 cells. In addition, CoQ0 impeded the ability of C. sakazakii to survive and replicate within RAW 264.7 cells. Finally, real-time polymerase chain reaction analysis confirmed that nine C. sakazakii genes associated with biofilm formation and virulence were downregulated in response to CoQ0 treatment. Overall, our findings suggest that CoQ0 is a promising antibiofilm agent and provide new insights for the prevention and control of infections caused by C. sakazakii.

Antimicrobial and Antibiofilm Efficacy and Mechanism of Oregano Essential Oil Against Shigella flexneri

The aim of this study was to assess the antimicrobial activity of oregano essential oil (OEO) against Shigella flexneri and eradication efficacy of OEO on biofilm. The results showed that the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of OEO against S. flexneri were 0.02% (v/v) and 0.04% (v/v), respectively. OEO effectively killed S. flexneri in Luria-Bertani (LB) broth and contaminated minced pork (the initial population of S. flexneri was about 7.0 log CFU/mL or 7.2 log CFU/g), and after treatment with OEO at 2 MIC in LB broth or at 15 MIC in minced pork, the population of S. flexneri decreased to an undetectable level after 2 or 9 h, respectively. OEO increased intracellular reactive oxygen species concentration, destroyed cell membrane, changed cell morphology, decreased intracellular ATP concentration, caused cell membrane depolarization, and destroyed proteins or inhibited proteins synthesis of S. flexneri. In addition, OEO effectively eradicated the biofilm of S. flexneri by effectively inactivating S. flexneri in mature biofilm, destroying the three-dimensional structure, and reducing exopolysaccharide biomass of S. flexneri. In conclusion, OEO exerts its antimicrobial action effectively and also has a valid scavenging effect on the biofilm of S. flexneri. These findings suggest that OEO has the potential to be used as a natural antibacterial and antibiofilm material in the control of S. flexneri in meat product supply chain, thereby preventing meat-associated infections.

Antibacterial Activity and Possible Mechanism of Litsea cubeba Essential Oil Against Shigella sonnei and Its Application in Lettuce

Shigella sonnei, the causative agents of bacillary dysentery, remains a significant threat to public health. Litsea cubeba essential oil (LC-EO), one of the natural essential oils, exhibited promising biological activities. In this study, the antibacterial effects and possible mechanisms of LC-EO on S. sonnei and its application in lettuce medium were investigated. The minimum inhibitory concentration (MIC) of LC-EO against S. sonnei ATCC 25931 and CMCC 51592 was 4 and 6 μL/mL, respectively. The LC-EO could inhibit the growth of S. sonnei, and decreased S. sonnei to undetectable levels with 4 μL/mL for 1 h in Luria-Bertani broth. The antibacterial mechanism indicated that after the treatment of LC-EO, the production of reactive oxygen species and the activity of superoxide dismutase were significantly elevated in S. sonnei cells, and eventually led to the lipid oxidation product, the malondialdehyde content that significantly increased. Moreover, LC-EO at 2 MIC could destroy 96.51% of bacterial cell membrane integrity, and made S. sonnei cells to appear wrinkled with a rough surface, so that the intracellular adenosine triphosphate leakage was about 0.352-0.030 μmol/L. Finally, the results of application evaluation indicated that the addition of LC-EO at 4 μL/mL in lettuce leaves and 6 μL/mL in lettuce juice could decrease the number of S. sonnei to undetectable levels without remarkable influence on the lettuce leaf sensory quality. In summary, LC-EO exerted strong antibacterial activity and has the potential to control S. sonnei in food industry.

Antibacterial Mechanism of Shikonin Against Vibrio vulnificus and Its Healing Potential on Infected Mice with Full-Thickness Excised Skin

Shikonin has anticancer, anti-inflammatory, and wound healing activities. Vibrio vulnificus is an important marine foodborne pathogen with a high fatality rate and rapid pathogenesis that can infect humans through ingestion and wounds. In this study, the antibacterial activity and possible antibacterial mechanism of shikonin against V. vulnificus were investigated. In addition, the ability of shikonin to control V. vulnificus infection in both pathways was assessed by artificially contaminated oysters and full-thickness excised skin-infected mice. Shikonin treatment can cause abnormal cell membrane function, as evidenced by hyperpolarization of the cell membrane, significant decreased intracellular ATP concentration (p < 0.05), significant increased intracellular reactive oxygen species and malondialdehyde content (p < 0.05), decreased cell membrane integrity, and changes in cell morphology. Shikonin at 40 and 80 μg/mL reduced bacterial numbers in shikonin-contaminated oysters by 3.58 and 2.18 log colony-forming unit (CFU)/mL. Shikonin can promote wound healing in mice infected with V. vulnificus by promoting the formation of granulation tissue, hair follicles, and sebaceous glands, promoting epithelial cell regeneration and epidermal growth factor production. These findings suggest that shikonin has a strong inactivation effect on V. vulnificus and can be used in food production and wound healing to effectively control V. vulnificus and reduce the number of diseases associated with it.

Antibiofilm effects of punicalagin against Staphylococcus aureus in vitro

Staphylococcus aureus is a common foodborne pathogen which can form biofilms to help them resist to antimicrobials. It brings great harm to human health. Punicalagin has good antimicrobial activities against S. aureus, but its effect on biofilm formation has not been clearly illustrated. The aim of this study was to explore the antibiofilm effects of punicalagin against S. aureus. Results showed that punicalagin did not significantly interfere with the growth of S. aureus at the concentrations of 1/64 MIC to 1/16 MIC. The biomass and metabolic activity of biofilms were significantly reduced when exposed to sub-inhibitory concentrations of punicalagin. The number of viable cells in the biofilms was also decreased after punicalagin treatment. Scanning electron microscopy and confocal laser scanning microscopy images confirmed that punicalagin damaged the structure of biofilms. The antibiofilm mechanism was partly due to the modification of the cell surface which led to the reduction of cell surface hydrophobicity. These findings suggest that punicalagin has the potential to be developed as an alternative to control S. aureus biofilms.

Antibacterial, antibiofilm, and antimotility signatures of some natural antimicrobials against Vibrio cholerae

Vibrio cholerae is an etiological cause of cholera and has been implicated in several epidemics. Exploration of the antimicrobial signatures of culinary spices has become an important industrial tool to suppress the growth of foodborne bacterial pathogens including Vibrio spp. The antibiofilm and antimotility activities of some selected natural antimicrobial agents were then evaluated. All the extracts showed vibriostatic activities with minimum inhibitory concentration (MIC) ranging from 0.1% to 0.4%. Cinnamon and black pepper demonstrated significant biofilm inhibition activity from 94.77% to 99.77% when administered at 100% MIC. Black pepper extract also demonstrated the highest biofilm inhibition activity against the established biofilms of V. cholerae O1 and O139. Cinnamon, calabash nutmeg, and black pepper significantly inhibited swimming and swarming motility by 85.51% to 94.87%. Sub-MICs (50% and 75%) of some extracts were also effective as an antibiofilm and antimotility agent against the tested strains. The findings of our study suggest the potential application of natural antimicrobial agents such as spices in food to inhibit biofilm formation and motility, which consequently mitigate the virulence and persistence of the pathogen in the food supply chain.

Antibacterial Activity of Thymoquinone Against Shigella flexneri and Its Effect on Biofilm Formation

Thymoquinone (TQ) has been demonstrated to have anti-cancer, anti-inflammatory, antioxidant, and anti-diabetic activities. Shigella flexneri is the main pathogen causing shigellosis in developing countries. In this study, the antibacterial activity of TQ against S. flexneri and its possible antibacterial mechanism were studied. In addition, the inhibitory effect of TQ on the formation of S. flexneri biofilm was also investigated. The results showed that both the minimum inhibitory concentration and the minimum bactericidal concentration of TQ against S. flexneri ATCC 12022 were 0.2 mg/mL. After treatment with TQ at 0.4 mg/mL in Luria-Bertani broth for 3 h, or treatment with 0.2 mg/mL TQ in phosphate-buffered saline for 60 min, the number of S. flexneri (initial number is 6.5 log colony-forming units/mL) dropped below the detection limit. TQ also displayed good antibacterial activity in contaminated lettuce juice. TQ caused an increase in intracellular reactive oxygen species level, a decrease in intracellular adenosine triphosphate (ATP) concentration, a change in the intracellular protein, damage to cell membrane integrity and changes in cell morphology. In addition, TQ showed the ability to inhibit the formation of S. flexneri biofilm; treatment resulted in a decrease in the amount of biofilm and extracellular polysaccharides, and the destruction of biofilm structure. These findings indicated that TQ had strong antimicrobial and antibiofilm activities and a potential to be applied in the fruit and vegetable processing industry or other food industries to control S. flexneri.

Antibacterial Activity and Mechanism of Linalool against Shigella sonnei and Its Application in Lettuce

Shigella sonnei (S. sonnei) infection accounted for approximately 75% of annual outbreaks of shigellosis, with the vast majority of outbreaks due to the consumption of contaminated foods (e.g., fresh vegetables, potato salad, fish, beef, etc.). Thus, we investigated the antibacterial effect and mechanism of linalool on S. sonnei and evaluated the effect of linalool on the sensory quality of lettuce. The minimum inhibitory concentration (MIC) of linalool against S. sonnei ATCC 25931 was 1.5 mg/mL. S. sonnei was treated with linalool at 1× MIC for 30 min and the amount of bacteria was decreased below the detection limit (1 CFU/mL) in phosphate-buffered saline (PBS) and Luria-Bertani (LB) medium. The bacterial content of the lettuce surface was reduced by 4.33 log CFU/cm² after soaking with linalool at 2× MIC. Treatment with linalool led to increased intracellular reactive oxygen species (ROS) levels, decreased intracellular adenosine-triphosphate (ATP) content, increased membrane lipid oxidation, damaged cell membrane integrity, and hyperpolarized cell membrane potential in S. sonnei. The application of linalool to lettuce had no effect on the color of lettuce compared to the control. The sensory evaluation results showed that linalool had an acceptable effect on the sensory quality of lettuce. These findings indicate that linalool played an antibacterial effect against S. sonnei and had potential as a natural antimicrobial for the inhibition of this foodborne pathogen.

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.

Juglone Inhibits Listeria monocytogenes ATCC 19115 by Targeting Cell Membrane and Protein

Foodborne disease caused by Listeria monocytogenes is a major global food safety problem. A potential solution is the antimicrobial development of the highly bioactive natural product juglone, yet few studies exist on its antibacterial mechanism against L. monocytogenes. Thus, we aimed to elucidate the antibacterial mechanism of action of juglone against L. monocytogenes by determining the resultant cell morphology, membrane permeability, membrane integrity, and proteome changes. The minimum inhibitory concentration of juglone against L. monocytogenes was 50 μg/mL, and L. monocytogenes treated with juglone had longer lag phases compared to controls. Juglone induced L. monocytogenes cell dysfunction, leakage of potassium ions, and membrane potential hyperpolarization. Confocal laser scanning microscopy and field-emission-gun scanning electron microscope assays revealed clear membrane damage due to juglone treatment. Fourier transform infrared analyses showed that L. monocytogenes responded to juglone by some conformational and compositional changes in the molecular makeup of the cell membrane. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that juglone either destroyed proteins or inhibited proteins synthesis in L. monocytogenes. Therefore, our findings established juglone as a natural antibacterial agent with potential to control foodborne L. monocytogenes infections.

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.

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.

Development of cationic peptide chimeric lysins based on phage lysin Lysqdvp001 and their antibacterial effects against Vibrio parahaemolyticus: A preliminary study

Cationic peptide chimeric lysins, Lysqdvp001-5aa, Lysqdvp001-10aa and Lysqdvp001-15aa, were designed based on lysin Lysqdvp001 from Vibrio parahaemolyticus (V. parahaemolyticus) phage qdvp001. These chimeric lysins showed equivalent peptidoglycan hydrolysis activities with Lysqdvp001 and could lyse the bacteria from the outside. The antibacterial activity as well as outer and inner membrane permeabilization of Lysqdvp001 and chimeric lysins against V. parahaemolyticus were Lysqdvp001-15aa>Lysqdvp001-10aa>Lysqdvp001-5aa>Lysqdvp001. Lysqdvp001-15aa exhibited an excellent antibacterial activity with minimum inhibition and bactericidal concentrations (MIC and MBC) of 0.2 and 0.4 mg/mL, respectively, and its antibacterial spectrum was much broader than phage qdvp001. Membrane hyperpolarization and membrane phospholipid exposure of V. parahaemolyticus were observed after Lysqdvp001-15aa treatments. Transmission electron microscope (TEM) showed Lysqdvp001-15aa destroyed structure integrity of V. parahaemolyticus. Besides, MIC and MBC of Lysqdvp001-15aa decreased V. parahaemolyticus counts in oyster by 3.20 and 4.03 log₁₀CFU/g. Lysqdvp001-15aa at MBC eradicated about 50% of V. parahaemolyticus biofilms and inhibited over 90% of the formation of the bacterial biofilms.

Antimicrobial Activity and Antibiofilm Potential of Coenzyme Q0 against Salmonella Typhimurium

Coenzyme Q₀ (CoQ₀) has anti-inflammatory and anti-tumor effects; however, the antimicrobial and antibiofilm activities of CoQ₀ against Salmonella enterica serovar Typhimurium are unknown. Thus, we investigated the bacteriostatic and antibiofilm activities, along with the underlying mechanism, of CoQ₀ against S. Typhimurium. The minimum inhibitory concentration (MIC) of CoQ₀ against S. enterica serovars Typhimurium was 0.1–0.2 mg/mL (549–1098 µM), and CoQ₀ at MIC and 2MIC decreased viable S. Typhimurium counts below detectable limits within 6 and 4 h, respectively. CoQ₀ at 20MIC (4 mg/mL) reduced S. Typhimurium on raw chicken by 1.5 log CFU/cm³ within 6 h. CoQ₀ effectively disrupted cell membrane integrity and induced morphological changes in the cell, resulting in hyperpolarization, decreased intracellular ATP concentrations, and cellular constituents leakage. Biofilm-associated S. Typhimurium cells were killed by CoQ₀ treatment. These findings suggest that CoQ₀ could be applied as a natural antibacterial substance for use against S. Typhimurium by the food industry.

Antibacterial effect of Blumea balsamifera (L.) DC. essential oil against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a common pathogenic bacteria in clinical environment, which can cause various diseases. Blumea balsamifera (L.) DC. as a traditional Chinese herb, its essential oil shows excellent bacteriostatic effect against S. aureus. To study the antibacterial effect of B. balsamifera (L.) DC. essential oil (BBO) against S. aureus, this study evaluated the effect of BBO on the permeability and integrity of cell membranes and on the total protein and nucleic acid content in S. aureus. Furthermore, proteomics was used to study the effect of BBO on the proteome of S. aureus. The results showed that BBO can destroy the permeability of the cell membrane, and inhibit the synthesis of bacterial nucleic acid and protein. Proteomics shows that BBO affects disorder of amino acid metabolism and affects the activity of various enzymes and the transport of substances. Taken together, these results indicated a substantial antibacterial effect of BBO on S. aureus.

Antimicrobial and anti-biofilm activity of thymoquinone against Shigella flexneri

Shigella flexneri (Sh. flexneri), a common foodborne pathogen, has become one of the main threats to food safety and human health due to its high pathogenicity and persistent infection. The objective of this study was to explore the antimicrobial and anti-biofilm activities and the possible mechanism of thymoquinone (TQ) against Sh. flexneri. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of TQ against Sh. flexneri were 0.4 and 0.5 mg/mL, respectively. TQ showed bactericidal activity against Sh. flexneri in culture medium and milk system. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) observations demonstrated that TQ could induce abnormal cell morphology and destroy cell membrane. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis suggested that TQ could inhibit protein synthesis in Sh. flexneri. Also, at sub-inhibitory concentrations (SICs), TQ exhibited an inhibitory effect on Sh. flexneri biofilm formation, which was confirmed by crystal violet quantitative analysis and SEM observation. Real-time quantitative PCR (RT-qPCR) analyses revealed that TQ downregulated the expression of genes involved in Sh. flexneri biofilm formation. Thus, TQ has potential as a natural antimicrobial and anti-biofilm agent to address the contamination and infection caused by Sh. flexneri. KEY POINTS: • Antimicrobial and anti-biofilm activity of TQ on Shigella flexneri were investigated. • TQ inhibited biofilm formation by Shigella flexneri. • TQ provided a new strategy for Shigella flexneri control.

Antibacterial activity and mechanism of three isomeric terpineols of Cinnamomum longepaniculatum leaf oil

α-Terpineol, terpinen-4-ol, and δ-terpineol, isomers of terpineol, are among the compounds that give Cinnamomum longepaniculatum leaf oil its distinguished pleasant smell. The objective of this study was to evaluate the antimicrobial activity of these three isomeric terpineols. The determination of antibacterial activity was based on the minimum inhibition concentration (MIC) and minimum bactericide concentration (MBC). Changes in time-kill curve, alkaline phosphatase (AKP), UV-absorbing material, membrane potential, and scanning electron microscopy (SEM) were measured to elucidate the possible antimicrobial mechanism. α-Terpineol, terpinen-4-ol, and δ-terpineol demonstrated good inhibitory effects against several gram-negative bacteria, particularly Shigella flexneri. MIC and MBC of α-terpineol and terpinen-4-ol were similar (0.766 mg/mL and 1.531 mg/mL, respectively) for S. flexneri, while the MIC and MBC values of δ-terpineol were 0.780 mg/mL and 3.125 mg/mL, respectively. Time-kill curves showed that the antibacterial activities of the tested compounds were in a concentration-dependent manner. Release of nucleic acids and proteins along with a decrease in membrane potential proved that α-terpineol, terpinen-4-ol, and δ-terpineol could increase the membrane permeability of Shigella flexneri. Additionally, the release of AKP suggested that the cell wall was destroyed. SEM analysis further confirmed that S. flexneri cell membranes were damaged by α-terpineol, terpinen-4-ol, and δ-terpineol. Our research suggests that these three isomeric terpineols have the potential of being used as natural antibacterial agents by destroying the cell membrane and wall, resulting in cell death. However, the specific antibacterial activity differences need further investigation.