Antimicrobial effect and mechanism of cinnamon oil and gamma radiation on Shewanella putrefaciens

Atmospheric cold plasma: A potential technology to control Shewanella putrefaciens in stored shrimp

This work aimed to investigate the inactivation mechanism of atmospheric cold plasma (ACP) against Shewanella putrefaciens both in PBS and sterile shrimp juice (SSJ). Reductions in cell density, cell viability, and biofilm formation activity were observed after ACP treatment. ACP cyclical treatment (1 min, 5 times) was more efficient than a one-time treatment (5 min, 1 time). After ACP cyclical treatment, the cell counts and cell viability of S. putrefaciens in PBS were decreased by 3.41 log CFU/mL and 85.30 %, respectively. As for SSJ group, the antibacterial efficiency of ACP declined, but the antibacterial effect of ACP cyclical treatment was still stronger than that of ACP one-time treatment. The biofilm formation activity of S. putrefaciens in PBS was almost completely inhibited, while it gradually returned to normal level with the prolonged of storage time for the SSJ counterpart. The rapid decrease in AKP activity after ACP treatment indicated the damage to cell wall integrity, which was also demonstrated by TEM. In addition, cell membrane and DNA damage of the strain also occurred after ACP treatment. The ROS fluorescence intensity in PBS was higher for the one-time treatment group, while the cyclical treatment group exhibited higher and more stable ozone levels. It was also detected that the total nitric oxide concentration in bacterial suspension depended on the dose of ACP treatment time. ACP treatment (35 kV) for 5 min, especially cyclical treatment, displayed its antibacterial properties on packaged shrimp contaminated with high concentration of S. putrefaciens. ACP cyclical treatment reduced surface bacterial counts of whole shrimps by 0.52 log CFU/mL, while ACP one-time treatment only achieved a decrease of 0.18 log CFU/mL. Therefore, ACP treatment could be considered as a potential alternative to enhance microbial control in food processing.

Effect and Mechanism of Eliminating Staphylococcus aureus by Electron Beam Irradiation and Reducing the Toxicity of Its Metabolites

The purpose of this study was to evaluate the mechanism of sterilization of Staphylococcus aureus by electron beam irradiation (0.5-, 1-, 2-, 4-, and 6-kGy treatments) and whether it reduces the toxicity of its fermentation supernatant. In this study, we investigated the mechanism of sterilization of S. aureus by electron beam irradiation using colony count, membrane potential, intracellular ATP, and UV absorbance measurements; we used hemolytic, cytotoxic, and suckling mouse wound models to verify that electron beam irradiation reduced the toxicity of the S. aureus fermentation supernatant. The results showed that 2 kGy of electron beam irradiation treatment completely inactivated S. aureus in suspension culture, and 4 kGy inactivated cells in S. aureus biofilms. This study suggests that the bactericidal effect of electron beam irradiation on S. aureus may be attributed to reversible damage to the cytoplasmic membrane, resulting in its leakage and the significant degradation of genomic DNA. The combined results of hemolytic, cytotoxic, and suckling mouse wound models demonstrated that the toxicity of S. aureus metabolites was significantly reduced when the electron beam irradiation dose was 4 kGy. In summary, electron beam irradiation has the potential to control S. aureus and reduce its toxic metabolites in food. IMPORTANCE Electron beam irradiation of >1 kGy damaged the cytoplasmic membrane, and reactive oxygen species (ROS) penetrated the cells. Electron beam irradiation of >4 kGy reduces the combined toxicity of virulent proteins produced by Staphylococcus aureus. Electron beam irradiation of >4 kGy can be used to inactivate Staphylococcus aureus and biofilms on milk.

Antibacterial activity of essential oils for combating colistin-resistant bacteria

OBJECTIVES

Colistin (polymyxin E) is a bactericidal antibiotic used to treat severe infections caused by multidrug-resistant Gram-negative bacteria. The product of the mcr1 gene generates transferrable plasmid-mediated colistin resistance, which has arisen as a worldwide healthcare problem. This study aimed to isolate, and identify colistin-resistant bacteria, and evaluate the ability of essential oils its fights.

METHODS

: Twenty-seven bacterial isolates were collected from patients who were admitted to National Cancer Institute, Cairo, Egypt, and processed by standard microbiological methods. Essential oils were purchased from AB chem company, Egypt, screened for antibacterial, cytotoxic activity, and (GC-MS) analysis.

RESULTS

A total of 5 bacterial isolates were resistant to colistin with minimum inhibitory concentration (MIC) ranging from 6.25->200µg/ml. Cinnamon oil exhibited the highest activity against colistin-resistant strains followed by thyme and eucalyptus oil. The (MIC) of cinnamon oils against resistant strains ranged from 4.88 to 312.5 µg/ml. Moreover, mcr-1 gene expression was extremely down-regulated after treatment of bacterial strains with cinnamon oil and decreased to 20-35-fold. Examination of treated bacterial cells with sub-inhibitory concentrations under transmission electron microscopy showed various abnormalities occurred in most of these cells.

CONCLUSIONS

cinnamon oil exhibits antibacterial activity against colistin-resistant strains, showing as a promising natural alternative in clinical therapy.

Inhibition of citral nanoemulsion to growth, spoilage ability and AI-2/luxS quorum sensing system of Shewanella putrefaciens CN-32: A study on bacteriostasis from in vitro culture and gene expression analysis

Objectives

The bacteriostatic effects of a citral nanoemulsion against Shewanella putrefaciens CN-32 (SHP CN-32) were investigated using in vitro culture and gene expression analysis, for building a potential application in spoilage microorganism control and aquatic products quality maintenance.

Materials and Methods

The SHP CN-32 was treated by prepared citral nanoemulsion when the minimal inhibitory concentration (MIC) was verified. The growth curve, membrane integrity, scanning electron microscope (SEM) observation, biofilm formation and quorum sensing (QS) signaling molecule AI-2 content were evaluated in different MIC treatment groups (0 MIC to 1.00 MIC). The gene expression status of SHP CN-32 in 0 MIC group and 0.50 MIC group were compared using transcriptome sequencing and quantitative PCR.

Results

The in vitro culture revealed that the citral nanoemulsion could inhibit the growth of SHP CN-32 with MIC of about 200 μg/ml. Images from membrane integrity, SEM and biofilm formation suggested significant biological structure damage in bacteria after treatment. Meanwhile, the quorum sensing (QS) signaling molecule AI-2 content showed a decline following the rise of treatment concentration. Transcriptome sequencing and quantitative PCR revealed that the majority genes related diversified functional metabolic pathways of SHP CN-32 were down-regulated at varying degree.

Conclusion

A significant bacteriostasis of citral nanoemulsion against Shewanella putrefaciens CN-32 (SHP CN-32) were verified via the results of growth inhibition, structural destruction, signal molecular decrease and gene expression down-regulation of strains. These synergies significantly affect the characteristic expression of SHP CN-32, revealing the application potential as bacteriostat, QS inhibitor and preservative in aquatic products.

Influence of Essential Oils on the Microbiological Quality of Fish Meat during Storage

Simple Summary

Fish meat is highly perishable due to its composition and the naturally present microbiota. The food industry aims to provide healthy, safe, and high-quality products to the market. Several strategies, including the use of natural preservatives, may be used to enhance food shelf life, and they can also be combined with others, such as vacuum packaging. This being the case, essential oils are natural plant components that, due to their composition, possess high antimicrobial and antioxidant effects, and are therefore good candidates to be tested as fish preservatives together with vacuum packaging. In the present study, essential oils from Citrus lemon and Cinnamomum camphora were added to rainbow trout meat for evaluating the microbiological quality (counts of bacteria and identification of present microbiota) of the fish when vacuum packed and stored for 7 days at 4 °C. Our results show that lemon (0.5% and 1%) as well as C. camphora essential oils (0.5% and 1%) had a positive effect on the microbiological quality of fish meat, keeping a high microbial quality of the fish fillets during 7 days of cold storage. The use of these essential oils in combination with vacuum packaging is beneficial in extending the shelf life of rainbow trout meat. All isolated species under the tested conditions are identified in the present study; such information will be useful for the future development of preservation methodologies that target isolated microorganisms, which will enable the food industry to enhance the shelf life and safety of fish.

Abstract

The aim of the present study was to evaluate the microbiological quality of rainbow trout meat treated with essential oils (EOs from Citrus limon and Cinnamomum camphora) at concentrations of 0.5% and 1.0% in combination with vacuum packaging during storage. The composition of the EOs were analyzed by gas chromatography coupled with mass spectrometry, and total viable counts (TVCs), coliform bacteria (CB), and lactic acid bacteria (LAB) were determined on the zeroth, first, third, fifth, and seventh days of storage at 4 °C. Individual species of isolated microorganisms were identified using a MALDI-TOF MS Biotyper. The results show that the major components of the EOs were linalool (98.1%) in C. camphora and α-limonene in C. limon. The highest number of TVCs and CB were 4.49 log CFU/g and 2.65 log CFU/g in aerobically packed samples at the seventh day. The lowest TVCs were those of samples treated with 1% C. camphora EO. For CB the most effective treatment was 1% lemon EO. LAB were only detected in a few samples, and were never present in aerobically packed samples; the highest number of LAB was 1.39 log CFU/g in samples treated with 1% lemon EO at day seven. The most commonly isolated coliform bacteria were Hafnia alvei, Serratia fonticola, Serratia proteamaculans, Pantoea agglomerans, and Yersinia ruckeri. Lactobacillus sakei, Staphylococcus hominis, and Carnobacterium maltaromaticum were the most frequently isolated bacteria from lactic acid bacteria. In conclusion, C. camphora EO at a concentration of 1% showed the highest antimicrobial activity.

Antifungal and mycotoxin detoxification ability of essential oils: A review

With increased popular awareness of food safety and environmental protection, plant essential oil has attracted interest due to the absence of residue, its high efficiency, antioxidant, immune regulation, antibacterial, insecticidal, and other advantages. Their application in degradation and elimination of mycotoxin toxicity has attracted increasing attention. This paper reviews the structure, antibacterial activity, antibacterial mechanism, and toxic effects of essential oils. The inhibitory effects of various essential oils on different mycotoxins were studied. The research progress on the inhibitory effects of plant essential oils on fungi and mycotoxins in recent years was summarized to provide reference for the application of plant essential oils.

Cinnamon Oil Inhibits Penicillium expansum Growth by Disturbing the Carbohydrate Metabolic Process

Penicillium expansum is a major postharvest pathogen that mainly threatens the global pome fruit industry and causes great economic losses annually. In the present study, the antifungal effects and potential mechanism of cinnamon oil against P. expansum were investigated. Results indicated that 0.25 mg L⁻¹ cinnamon oil could efficiently inhibit the spore germination, conidial production, mycelial accumulation, and expansion of P. expansum. In addition, it could effectively control blue mold rots induced by P. expansum in apples. Cinnamon oil could also reduce the expression of genes involved in patulin biosynthesis. Through a proteomic quantitative analysis, a total of 146 differentially expressed proteins (DEPs) involved in the carbohydrate metabolic process, most of which were down-regulated, were noticed for their large number and functional significance. Meanwhile, the expressions of 14 candidate genes corresponding to DEPs and the activities of six key regulatory enzymes (involving in cellulose hydrolyzation, Krebs circle, glycolysis, and pentose phosphate pathway) showed a similar trend in protein levels. In addition, extracellular carbohydrate consumption, intracellular carbohydrate accumulation, and ATP production of P. expansum under cinnamon oil stress were significantly decreased. Basing on the correlated and mutually authenticated results, we speculated that disturbing the fungal carbohydrate metabolic process would be partly responsible for the inhibitory effects of cinnamon oil on P. expansum growth. The findings would provide new insights into the antimicrobial mode of cinnamon oil.

Punicalagin Damages the Membrane of Salmonella Typhimurium

Salmonella, a bacterial foodborne pathogen, can contaminate meat, milk, and vegetables. While appropriate measures are available to control Salmonella, the inhibitory phytochemicals from plants are gaining increased attention. Punicalagin, a natural antimicrobial, is one of the main active tannins isolated from Punica granatum L. To obtain a broader understanding of the effect of punicalagin on the cell membranes of Salmonella Typhimurium, the growth curves, extracellular potassium concentration, release of cell constituents, intracellular pH, membrane potential, and morphological features were characterized to elucidate the mechanisms of action. Treatment with punicalagin induced an increase in the extracellular concentrations of potassium and a release of cell constituents. A higher pH gradient, an increase in the intracellular pH, and cell membrane depolarization were observed after punicalagin treatment. Electron microscopy observations showed that the cell membrane structures of Salmonella Typhimurium were damaged by punicalagin. It is concluded that punicalagin inhibits the proliferation of Salmonella Typhimurium and destroys the integrity of the cell membrane, leading to a loss of cell homeostasis. These findings indicate that punicalagin has the potential to be developed as a future alternative to control Salmonella Typhimurium contamination in foods and reduce the risk of salmonellosis.

Elucidating Antibacterial Activity and Mechanism of Daphnetin against Pseudomonas fluorescens and Shewanella putrefaciens

In this research, the antibacterial activity and mechanism of daphnetin against Pseudomonas fluorescens and Shewanella putrefaciens were evaluated. The minimum inhibitory concentration (MIC) of daphnetin on P. fluorescens and S. putrefaciens was 0.16 and 0.08 mg·mL−1, respectively. The growth curve test also showed that daphnetin had a good antibacterial effect. The results of intracellular component leakage and cell viability analysis illustrated that daphnetin destroyed the morphology of the cell membrane. According to scanning electron microscope and transmission electron microscope observations, the treated bacterial cells displayed obvious morphological and ultrastructural changes in the cell membrane of the two tested strains, whichconfirmed daphnetin’s damage to the integrity of the cell membrane. The findings indicated that daphnetin mainly exerted its antibacterial effect by destroying the membrane and suggested that it had good potential to be as a natural food preservative.

A transcriptome analysis of the antibacterial mechanism of flavonoids from Sedum aizoon L. against Shewanella putrefaciens

Flavonoids from Sedum aizoon L. (FSAL) possess prominent antibacterial activity against Shewanella putrefaciens isolated from sea food. In the current study, the involved molecular mechanisms were investigated using transcriptome analyses combined with bioinformatics analysis in vitro for the first time. Results showed that treatment of FSAL (1.0 MIC) damaged the permeability and integrity of cell membrane and induced 721 differentially expressed genes (DEGs) in tested bacteria at transcriptional levels, including 107 DEGs were up-regulated and 614 DEGs were down-regulated. In addition, the RNA-Seq analysis revealed that the majority of DEGs mainly involved in pathways of lipopolysaccharide biosynthesis, glycerophospholipid metabolism, biosynthesis of amino acids, purine metabolism, ABC transporters and response to stimulus. In summary, the integrated results indicated that the intervention of FSAL induced destruction of cell wall and membrane, disorder of the metabolic process and redox balance, and damage of nucleic acids in S. putrefaciens, at last resulted in the death of cells. This study provided new insights into the anti- S. putrefaciens molecular mechanism underlying the treatment of FSAL, which may be served as the basis guide for identifying potential antimicrobial targets and application of FSAL in food safety.

Microbial radiosensitization using combined treatments of essential oils and irradiation- part B: Comparison between gamma-ray and X-ray at different dose rates

Stored rice and rice products are prone to contamination by pathogenic fungi and bacteria such as Aspergillus niger, Bacillus cereus, and Paenibacillus amylolyticus. Treatment with antimicrobial essential oils (EOs) and irradiation are options to control spoilage organisms. Microbial samples with or without fumigation with an oregano/thyme EO mixture were irradiated at 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 kGy for calculation of a D₁₀ value. The relative sensitivity was calculated as the ratio of D10 values for the irradiation plus oregano and thyme EO combination and irradiation alone treatments. In all cases, irradiation plus fumigation with the oregano and thyme EO mixture showed increased efficacy compared with irradiation alone. The relative sensitivity of γ-ray irradiation against A. niger was 1.22, 1.33, and 1.24 for radiation dose rates of 10.445, 4.558, and 0.085 kGy/h, respectively, however against B. cereus it was 1.28, 1.45, and 1.49, and against P. amylolyticus it was 1.35, 1.33, and 1.38, for respective γ-ray irradiation dose rates. The relative sensitivity of X-ray irradiation against A. niger, B. cereus, and P. amylolyticus was 1.63, 1.21, and 1.31, respectively, at the X-ray dose rate of 0.76 kGy/h. The results showed that the relative sensitivity of γ-ray irradiation was higher against the two bacteria than the fungus, whereas X-ray showed higher sensitivity against the fungus than the two bacteria. There was no consistent positive or negative relationship between dose rate and relative sensitivity. The results demonstrated the potential of an oregano and thyme EOs mixture as an antimicrobial agent and its efficacy to increase the radiosensitization of A. niger, B. cereus, and P. amylolyticus during γ-ray or X-ray irradiation treatments.

ε-Polylysine Inhibits Shewanella putrefaciens with Membrane Disruption and Cell Damage

ε-Polylysine (ε-PL) was studied for the growth inhibition of Shewanella putrefaciens (S. putrefaciens). The minimal inhibitory concentration (MIC) of ε-PL against S. putrefaciens was measured by the broth dilution method, while the membrane permeability and metabolism of S. putrefaciens were assessed after ε-PL treatment. Additionally, growth curves, the content of alkaline phosphatase (AKP), the electrical conductivity (EC), the UV absorbance and scanning electron microscope (SEM) data were used to study cellular morphology. The impact of ε-PL on cell metabolism was also investigated by different methods, such as enzyme activity (peroxidase [POD], catalase [CAT], succinodehydrogenase [SDH] and malic dehydrogenase [MDH]) and cell metabolic activity. The results showed that the MIC of ε-PL against S. putrefaciens was 1.0 mg/mL. When S. putrefaciens was treated with ε-PL, the growth of the bacteria was inhibited and the AKP content, electrical conductivity and UV absorbance were increased, which demonstrated that ε-PL could damage the cell structure. The enzyme activities of POD, CAT, SDH, and MDH in the bacterial solution with ε-PL were decreased compared to those in the ordinary bacterial solution. As the concentration of ε-PL was increased, the enzyme activity decreased further. The respiratory activity of S. putrefaciens was also inhibited by ε-PL. The results suggest that ε-PL acts on the cell membrane of S. putrefaciens, thereby increasing membrane permeability and inhibiting enzyme activity in relation to respiratory metabolism and cell metabolism. This leads to inhibition of cell growth, and eventually cell death.