Effects of citronellal on growth and enterotoxins production in Staphylococcus aureus ATCC 29213

Acute toxicity and anti-enterotoxigenic activity of pigment extracted from Micrococcus roseus

Microbial pigments are considered as one of the main sources of natural types, and the attention to them is increasing in the food and pharmaceutical industries. This study aimed to investigate the effects of pigments extracted from Micrococcus roseus (PEM) on the gene expression of a and b staphylococcal enterotoxins (sea and seb) and their acute toxicity. Real-time PCR was used to study the anti-enterotoxigenic activity of PEM against Staphylococcus aureus at sub-inhibitory concentrations. In addition, the acute toxicity of PEM was evaluated on albino mice through alkaline phosphatase (ALP), aspartate aminotransferas (AST), and alanine aminotransferase (ALT) of liver and its histopathological changes. Based on the results, the expression of sea and seb was decreased in the presence of PEM at sub-inhibitory concentrations. The 2-∆∆CT was measured 0.02 and 0.01 for the expression of sea and seb of S. aureus grown in the MHB containing 16 mg/ml PEM. The results showed that the expression of seb is more sensitive to PEM compared to the expression of sea. After treatment of mice with PEM for two weeks, the condition of mice was normal, and the results of liver enzymatic activities and histopathological changes showed insignificant difference compared to the control sample.

Inhibitory effects of citral on the production of virulence factors in Staphylococcus aureus and its potential application in meat preservation

Foodborne diseases caused by Staphylococcus aureus contamination on meat and meat products has gained increasing attention in recent years, while the pathogenicity of S. aureus is mainly attributed to its virulence factors production, which is primarily regulated by quorum sensing (QS) system. Herein, we aimed to uncover the inhibitory effects and mechanisms of citral (CIT) on virulence factors production by S. aureus, and further explore its potential application in pork preservation. Susceptibility test confirmed the antibacterial properties of CIT against S. aureus, the minimal inhibitory concentration (MIC) was 0.25 mg/mL. Treatment with sub-MICs of CIT reduced the hemolytic activity by inhibiting the production of α-hemolysin, and staphylococcal enterotoxins (SEs) production was significantly inhibited by CIT in both culture medium and pork without affecting bacterial growth. Transcriptomic analysis indicated that the differentially expression genes encoding α-hemolysin, SEs, and other virulence factors were down-regulated after treatment with 1/2MIC CIT. Moreover, the genes related to QS including agrA and agrC were also down-regulated, while the global transcriptional regulator sarA was up-regulated. Data here demonstrated that CIT could inhibited S. aureus virulence factors production through disturbing QS systems. In a challenge test, the addition of CIT caused a remarkable inhibition of S. aureus population and delay in lipid oxidation and color change on pork after 15 days incubation at 4 °C. These findings demonstrated that CIT could not only efficiently restrain the production of S. aureus virulence factors by disturbing QS, but also exhibit the potential application on the preservation of meat products.

Effect of allyl isothiocyanate on the growth and virulence of Clostridium perfringens and its application on cooked pork

The objective of this study is to explore the antibacterial action modes and virulence-inhibitory effects of allyl isothiocyanate (AITC) against Clostridium perfringens (C. perfringens). The minimum inhibitory concentration (MIC) of AITC against vegetative cells of Cp 13124 was 0.1 μL/mL, and the time-kill kinetics analysis revealed that AITC could significantly suppress the growth of Cp 13124. According to the results from scanning electron microscopy (SEM), fluorescence microscopy, and UV absorbance substance detection, the cell membrane of Cp 13124 was damaged upon AITC treatment, causing a loss of integrity and the release of intracellular substances. Meanwhile, the fluorescence quenching experiment indicated the interaction of AIT-C with membrane proteins, which caused changes in the conformation of membrane proteins. Measurement of reactive oxygen species (ROS) and flow cytometry analysis demonstrated that AITC could induce apoptosis through oxidative stress. The formation of Cp 13124 biofilms was inhibited by AITC using the crystalline violet method, which was possibly related to the inhibition of sliding motility. Finally, low concentrations of AITC could be used as an antibacterial agent to inhibit the outgrowth of Cp 13124 in cooked pork, suggesting that AITC is a promising candidate for novel preservatives in the meat business.

Tea Polyphenols Inhibit the Activity and Toxicity of Staphylococcus aureus by Destroying Cell Membranes and Accumulating Reactive Oxygen Species

Staphylococcus aureus can cause bacterial food intoxication and seriously affect human health. Tea polyphenols (TP) are a kind of natural, safe, and broad-spectrum bacteriostatic substances, with a wide range of bacteriostatic effects. In the study, we explored the possible bacteriostatic mode of TP. The minimum inhibitory concentration of TP against S. aureus was 64 μg/mL. Protein, DNA, and K+ leak experiments, fluorescence microscopy, and transmission electron microscopy suggested that TP disrupt cell membranes, leading to intracellular component loss. By studying the effect of TP on the toxicity of S. aureus, it was found that the expression levels of two toxin genes, coa and spa, were downregulated by 2.37 and 32.6, respectively. Furthermore, after treatment with TP, a large number of reactive oxygen species (ROS) were propagated and released, leading to oxidative stress in cells. We speculated that the bacteriostatic mechanism of TP may be through the destruction of the cell membrane and ROS-mediated oxidative stress. Meanwhile, the hemolysis activity proved the safety of TP. Our results suggested that TP may be a potential antimicrobial agent for food.

Plant Antimicrobials for Food Quality and Safety: Recent Views and Future Challenges

The increasing demand for natural, safe, and sustainable food preservation methods drove research towards the use of plant antimicrobials as an alternative to synthetic preservatives. This review article comprehensively discussed the potential applications of plant extracts, essential oils, and their compounds as antimicrobial agents in the food industry. The antimicrobial properties of several plant-derived substances against foodborne pathogens and spoilage microorganisms, along with their modes of action, factors affecting their efficacy, and potential negative sensory impacts, were presented. The review highlighted the synergistic or additive effects displayed by combinations of plant antimicrobials, as well as the successful integration of plant extracts with food technologies ensuring an improved hurdle effect, which can enhance food safety and shelf life. The review likewise emphasized the need for further research in fields such as mode of action, optimized formulations, sensory properties, safety assessment, regulatory aspects, eco-friendly production methods, and consumer education. By addressing these gaps, plant antimicrobials can pave the way for more effective, safe, and sustainable food preservation strategies in the future.

Bacteriostatic Effects of Yujin Powder and Its Components on Clinical Isolation of Multidrug-Resistant Avian Pathogenic Escherichia coli

Escherichia coli is one of the most common pathogenic bacteria in diarrheal chickens, leading to serious economic losses in the poultry industry. The limited effect of antibiotics on antibiotic-resistant E. coli makes this bacterium a potential threat to human health. Yujin powder (YJP) has been reported as an agent that releases the symptoms caused by E. coli for a long time. The objective of this study is to investigate the effect of Yujin powder (YJP) and its components, Scutellariae Radix (SR) and Baicalin (Bac), anti-against multi-drug-resistant E. coli in vitro and in vivo. A multi-drug-resistant bacteria was isolated and identified from a clinical diarrheal chick. Then, the anti-bacterial effects of drugs were assessed in vitro and in vivo by analyzing the bacteria loads of organs, the levels of endotoxin, TNF-α, IL-1β, and IL-6 of the serum. Results found that the pathogenic E. coli was resistant to 19 tested antibiotics. YJP, SR, and Bac could directly inhibit the growth of this strain at high concentrations in vitro, and presents obvious anti-bacterial effects by reducing the bacterial loads, the release of endotoxin, and inflammation in vivo, which was much more effective than the resistant antibiotic ciprofloxacin. This study demonstrates that those natural medicines have the potential to be used as novel treatments to treat the disease caused by this isolated MDREC strain.

Recent Advances in PLA-Based Antibacterial Food Packaging and Its Applications

In order to reduce environmental pollution and resource waste, food packaging materials should not only have good biodegradable ability but also effective antibacterial properties. Poly(lactic acid) (PLA) is the most commonly used biopolymer for food packaging applications. PLA has good physical properties, mechanical properties, biodegradability, and cell compatibility but does not have inherent antibacterial properties. Therefore, antibacterial packaging materials based on PLA need to add antibacterial agents to the polymer matrix. Natural antibacterial agents are widely used in food packaging materials due to their low toxicity. The high volatility of natural antibacterial agents restricts their application in food packaging materials. Therefore, appropriate processing methods are particularly important. This review introduces PLA-based natural antibacterial food packaging, and the composition and application of natural antibacterial agents are discussed. The properties of natural antibacterial agents, the technology of binding with the matrix, and the effect of inhibiting various bacteria are summarized.

Anti-browning effects of citronellal on fresh-cut taro (Colocasia esculenta) slices under cold storage condition

The browning on the cut surface is a big problem reducing the quality of fresh-cut taro (FCT), which causes severe postharvest losses and may raise environmental impacts. Citronellal (CA) is a natural compound in several aromatic plants. This study investigated the effects of CA treatments in different concentrations (0.2, 0.5, and 1 mL/L) on the browning of FCT under cold storage at 5°C. The results indicated that low-dose (0.2 mL/L) CA treatment showed best anti-browning effects, reflecting at the maintained L* values but the reduced a*, b* and browning index values by CA treatment during cold storage. A repeated experiment using 0.2 mL/L CA confirmed fine anti-browning effects again. Furthermore, CA (0.2 mL/L) treatment markedly reduced the contents of total phenolic compounds and soluble quinones, restrained the activities of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase, down-regulated the gene expression of 18 browning-related enzymes in FCT. These results together strongly demonstrate the validity of CA on FCT browning prevention. Given that CA is a natural compound existing in plants, low concentration of CA possesses strong anti-browning effects on FCT and also inhibitory effects on pathogens, implying that its application has potentiality to preserve high quality of fresh-cut produce for processing and storage. Moreover, CA treatment significantly decreased malondialdehyde contents and lipoxygenase activity. Correlation analysis indicated that the lipid peroxidation of cell membrane was mostly correlated with FCT browning. The results suggest that membrane lipid peroxidation was a possible reason for FCT browning and CA treatment reduced browning, in part, through alleviating the lipid peroxidation of cell membrane. Overall, our results demonstrate that CA is a novel browning mitigator for FCT under cold storage condition.