Sodium Chloride Does Not Ensure Microbiological Safety of Foods: Cases and Solutions

Potential of phytic acid in synergy with sodium chloride as a natural-borne preservative to inactivate Escherichia coli O157:H7 and inhibit natural microflora in fresh noodles at room temperature

The increase in consumer demand and the high cost of maintaining a cold chain during distribution emphasize the need for preservative technology to ensure the microbiological quality of fresh noodles with a moisture content of 32-40%. However, few studies have been conducted to increase the storage stability of fresh noodles by using a preservative with a significant inhibitory effect against microorganisms and/or minimizing the use of synthetic antimicrobial agents. This study aimed to propose a synergistic natural-borne antimicrobial that could interact with NaCl, an essential component of noodles, for extended preservation of fresh noodles at room temperature. NaCl (0-1.6% (w/w) based on the total weight of the noodle dough) and phytic acid (0-1.0% (v/w)) were applied to fresh noodles. The bactericidal effect on Escherichia coli O157:H7 and the inhibitory effect on the indigenous microflora were assessed within 21 days at 30 °C. After cooking fresh noodles, physicochemical/textural and sensory characteristics (whiteness, pH, water activity; hardness, adhesiveness, springiness, chewiness; appearance, odor, overall acceptance) were further evaluated as objective and subjective quality parameters. In fresh noodles preserved with 0.6% phytic acid and 1.6% NaCl, the E. coli O157:H7 population was eliminated below the detection limit (>5.8 log reduction; P < 0.05) within 4 days of storage. This preservative significantly inhibited (P < 0.05) the mesophilic bacterial and total yeast/mold counts naturally present in fresh noodles for 12 days, while the largest antimicrobial activity was observed in noodles supplemented with 1.0% phytic acid combined with 1.0-1.6% NaCl. Although the objective parameters were significantly affected by the preservatives, analysis of the subjective parameters demonstrated that all samples were slightly or moderately favored by the panelists (P > 0.05). Considering the normal range of objective parameters for fresh noodles, the optimal preservative was determined to be 0.6% phytic acid and 1.6% NaCl. This study suggests the potential use of phytic acid as a natural-borne preservative that combines with NaCl in fresh noodles and exerts a synergistic effect. The developed method is expected to be applicable to extending the shelf life of other grain-based foods containing NaCl as an essential ingredient.

Factors influencing age at onset of colorectal polyps and benefit-finding after polypectomy

Screening, followed by colonoscopic polypectomy, has been widely performed in China. However, factors influencing age at onset of colorectal polyps and benefit-finding after polypectomy have been insufficiently studied or ignored. A total of 152 patients with colorectal polyps first detected in First Affiliated Hospital of Huzhou University from July to September 2022 were enrolled in this study. We selected 11 factors associated with the risk of colorectal polyps, including gender, body mass index, occupational stress, education level, income satisfaction, smoking, alcohol consumption, exercise frequency, diet, family history and polyp characteristics. Benefit-finding after polypectomy was obtained by follow-up for 142 of these patients. Multivariate linear regression analysis showed that being overweight (i.e., body mass index ≥25 kg/m2), higher education level, lower exercise frequency, and refrigerated food preference were associated with early-onset colorectal polyps. Patients with a preference for pickled food and age ≥50 years at first colorectal polyp detection had lower benefit findings after colonoscopic polypectomy. Colorectal polyps may develop earlier in people who are overweight, well-educated, exercise less, and prefer refrigerated food. In addition, patients who prefer pickled food and age at onset ≥50 years have lower benefit-finding requiring more attention in future colonoscopy follow-ups.

CodY: An Essential Transcriptional Regulator Involved in Environmental Stress Tolerance in Foodborne Staphylococcus aureus RMSA24

Staphylococcus aureus (S. aureus), as the main pathogen in milk and dairy products, usually causes intoxication with vomiting and various kinds of inflammation after entering the human body. CodY, an important transcriptional regulator in S. aureus, plays an important role in regulating metabolism, growth, and virulence. However, little is known about the role of CodY on environmental stress tolerance. In this research, we revealed the role of CodY in environmental stress tolerance in foodborne S. aureus RMSA24. codY mutation significantly reduced the tolerance of S. aureus to desiccation and oxidative, salt, and high-temperature stresses. However, S. aureus was more tolerant to low temperature stress due to mutation of codY. We found that the expressions of two important heat shock proteins-GroEL and DanJ-were significantly down-regulated in the mutant codY. This suggests that CodY may indirectly regulate the high- and low-temperature tolerance of S. aureus by regulating the expressions of groEL and danJ. This study reveals a new mechanism of environmental stress tolerance in S. aureus and provides new insights into controlling the contamination and harm caused by S. aureus in the food industry.

Impact of the Food-Related Stress Conditions on the Expression of Enterotoxin Genes among Staphylococcus aureus

Staphylococcus aureus is one of the most important foodborne pathogens. S. aureus has the capability to produce a variety of toxins, including staphylococcal enterotoxins (SEs). The aim of this study was to evaluate the survival rate of S. aureus cells and analyze enterotoxins gene expression after exposure to osmotic stress and acidic/alkaline stress. To determine survival rates, the traditional plate counting method and flow cytometry were used. The expression levels of the enterotoxin genes were performed by quantitative reverse transcription PCR (RT-qPCR). Expression changes differed depending on the stressors chosen. The obtained results in this study showed the effect of critical food-related stress conditions on SE gene expression in S. aureus. The study showed different expression levels of the tested enterotoxins genes depending on the stress. The most tested enterotoxin genes (seg, sei, and selo) after exposure to pH = 4.5 stress have similar expression as in the optimal condition. After alkaline treatment (pH = 9.6), a similar expression gene value as for the optimal condition was observed. The analysis of gene expression in response to stress caused by NaCl, showed that the expression of selp decreased, whereas selu, selm, and selo genes increased. A significantly decreased expression of the sea gene was observed.

A novel gdmH-related gene, ghl, involved in environmental stress tolerance and vancomycin susceptibility in milk-derived Staphylococcus aureus

Staphylococcus aureus is one of the main microorganisms that contaminate dairy products and pickled foods, and has a great impact on economy and human health. GdmH-related proteins, as important functional units widely present in Staphylococcus species, have not been reported in S. aureus so far. In this study, we identified a gdmH-related gene, named ghl. We found that mutation of ghl gene could decrease the tolerance of environmental stresses (heat, desiccation, salt and hydrogen peroxide) of S. aureus and enhanced the capacities of biofilm formation. In addition, the ghl mutant was more sensitive to vancomycin on CAMHB solid plates but more resistant to vancomycin in CAMHB liquid medium compared to wild type RMSA24. These results indicated that ghl is an important factor to respond to environmental stress in foodborne S. aureus. This paper for the first time reported that a GdmH-related protein plays an important role in environmental tolerance, providing a new direction for the follow-up study of GdmH-related proteins, as well as a potential target gene for further research on the tolerance mechanism of Staphylococcus aureus in food processing and the control of biofilm formation.

Therapeutic application of carvacrol: A comprehensive review

Carvacrol is a major natural constituent and is significantly present as an essential oil in aromatic plants and is well known for its numerous biological activities. Therapeutic properties of carvacrol have been demonstrated as anti-oxidant, anticancer, diabetes prevention, cardioprotective, anti-obesity, hepatoprotective and reproductive role, antiaging, antimicrobial, and immunomodulatory properties. The carvacrol biosynthesis has been mediated through mevalonate pathway. Carvacrol has the anticancer ability against malignant cells via decreasing the expressions of matrix metalloprotease 2 and 9, inducing apoptosis, enhancing the expression of pro-apoptotic proteins, disrupting mitochondrial membrane, suppressing extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase signal transduction, and also decreasing the phosphoinositide 3-kinase/protein kinase B. It also decreased the concentrations of alanine aminotransferase, alkaline phosphatase and aspartate aminotransferase, and gamma-glutamyl transpeptidase as well as also restored liver function, insulin level, and plasma glucose level. Carvacrol also has been found to exert antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, Coagulase-negative staphylococcus, Salmonella spp., Enterococcus sp. Shigella, and Escherichia coli. The current review article summarizes the health-promoting perspectives of carvacrol through various pathways.

The Response and Survival Mechanisms of Staphylococcus aureus under High Salinity Stress in Salted Foods

Staphylococcus aureus (S. aureus) has a strong tolerance to high salt stress. It is a major reason as to why the contamination of S. aureus in salted food cannot be eradicated. To elucidate its response and survival mechanisms, changes in the morphology, biofilm formation, virulence, transcriptome, and metabolome of S. aureus were investigated. IsaA positively regulates and participates in the formation of biofilm. Virulence was downregulated to reduce the depletion of nonessential cellular functions. Inositol phosphate metabolism was downregulated to reduce the conversion of functional molecules. The MtsABC transport system was downregulated to reduce ion transport and signaling. Aminoacyl-tRNA biosynthesis was upregulated to improve cellular homeostasis. The betaine biosynthesis pathway was upregulated to protect the active structure of proteins and nucleic acids. Within a 10% NaCl concentration, the L-proline content was upregulated to increase osmotic stability. In addition, 20 hub genes were identified through an interaction analysis. The findings provide theoretical support for the prevention and control of salt-tolerant bacteria in salted foods.

The effects of vegetable pickling conditions on the dynamics of microbiota and metabolites

Background

Salting is a traditional procedure for producing pickled vegetables. Salting can be used as a pretreatment, for safe lactic acid fermentation and for salt stock preparation. This study aimed to provide valuable knowledge to improve pickle production by investigating the dynamics of microbiota and metabolites during the pretreatment and salt stock preparation processes, which have previously been overlooked. The differences in these process conditions would be expected to change the microbiota and consequently influence the content of metabolites in pickles.

Methods

Samples, collected from eight commercial pickle manufacturers in Japan, consisted of the initial raw materials, pickled vegetables and used brine. The microbiota were analyzed by 16S rRNA sequencing and the metabolites quantified by liquid chromatograph-mass spectrometry. Statistical analyses helped to identify any significant differences between samples from the initial raw materials, pretreatment process and salt stock preparation process groups.

Results

Under pretreatment conditions, aerobic and facultative anaerobic bacteria were predominant, including Vibrio, a potentially undesirable genus for pickle production. Under salt stock preparation conditions, the presence of halophilic bacteria, Halanaerobium, suggested their involvement in the increase in pyruvate derivatives such as branched-chain amino acids (BCAA). PICRUSt analysis indicated that the enhanced production of BCAA in salt stock was caused not by quantitative but by qualitative differences in the biosynthetic pathway of BCAA in the microbiota.

Conclusion

The differences in the microbiota between pretreatment and previously studied lactic acid fermentation processes emphasized the importance of anaerobic conditions and low pH under moderate salinity conditions for assuring safe pickle production. The results from the salt stock preparation process suggested that the Halanaerobium present may provide a key enzyme in the BCAA biosynthetic pathway which prefers NADH as a coenzyme. This feature can enhance BCAA production under anaerobic conditions where NADH is in excess. The effects shown in this study will be important for adjusting pickling conditions by changing the abundance of bacteria to improve the quality of pickled vegetables.

Targeting Mannitol Metabolism as an Alternative Antimicrobial Strategy Based on the Structure-Function Study of Mannitol-1-Phosphate Dehydrogenase in Staphylococcus aureus

Mannitol-1-phosphate dehydrogenase (M1PDH) is a key enzyme in Staphylococcus aureus mannitol metabolism, but its roles in pathophysiological settings have not been established. We performed comprehensive structure-function analysis of M1PDH from S. aureus USA300, a strain of community-associated methicillin-resistant S. aureus, to evaluate its roles in cell viability and virulence under pathophysiological conditions. On the basis of our results, we propose M1PDH as a potential antibacterial target. In vitro cell viability assessment of ΔmtlD knockout and complemented strains confirmed that M1PDH is essential to endure pH, high-salt, and oxidative stress and thus that M1PDH is required for preventing osmotic burst by regulating pressure potential imposed by mannitol. The mouse infection model also verified that M1PDH is essential for bacterial survival during infection. To further support the use of M1PDH as an antibacterial target, we identified dihydrocelastrol (DHCL) as a competitive inhibitor of S. aureus M1PDH (SaM1PDH) and confirmed that DHCL effectively reduces bacterial cell viability during host infection. To explain physiological functions of SaM1PDH at the atomic level, the crystal structure of SaM1PDH was determined at 1.7-Å resolution. Structure-based mutation analyses and DHCL molecular docking to the SaM1PDH active site followed by functional assay identified key residues in the active site and provided the action mechanism of DHCL. Collectively, we propose SaM1PDH as a target for antibiotic development based on its physiological roles with the goals of expanding the repertory of antibiotic targets to fight antimicrobial resistance and providing essential knowledge for developing potent inhibitors of SaM1PDH based on structure-function studies.IMPORTANCE Due to the shortage of effective antibiotics against drug-resistant Staphylococcus aureus, new targets are urgently required to develop next-generation antibiotics. We investigated mannitol-1-phosphate dehydrogenase of S. aureus USA300 (SaM1PDH), a key enzyme regulating intracellular mannitol levels, and explored the possibility of using SaM1PDH as a target for developing antibiotic. Since mannitol is necessary for maintaining the cellular redox and osmotic potential, the homeostatic imbalance caused by treatment with a SaM1PDH inhibitor or knockout of the gene encoding SaM1PDH results in bacterial cell death through oxidative and/or mannitol-dependent cytolysis. We elucidated the molecular mechanism of SaM1PDH and the structural basis of substrate and inhibitor recognition by enzymatic and structural analyses of SaM1PDH. Our results strongly support the concept that targeting of SaM1PDH represents an alternative strategy for developing a new class of antibiotics that cause bacterial cell death not by blocking key cellular machinery but by inducing cytolysis and reducing stress tolerance through inhibition of the mannitol pathway.