Sodium dehydroacetate confers broad antibiotic tolerance by remodeling bacterial metabolism

Effect of emodin on Streptococcus suis by targeting β-ketoacyl-acyl carrier protein synthase Ⅱ

BACKGROUND

Streptococcus suis is a zoonotic pathogen that causes meningitis, septicaemia, endocarditis, arthritis, and pneumonia in human beings. With the increasing prevalence of S. suis infections and a general decline in the effectiveness of antibiotics, the development of novel drugs that have effect on S. suis is extremely urgent. Emodin, a natural anthraquinone derivative of Rheum palmatum L., Reynoutria japonica Houtt., Polygonum multiflorum Thunb. and Cassia obtusifolia L., has been reported to exert anti-S. suis effect; however, the specific mechanism of the anti-S. suis action by targeting β-ketoacyl-acyl carrier protein synthase Ⅱ (FabF) in the fatty acid synthesis pathway remains unexplored.

PURPOSE

We sought to reveal the potential role of emodin to prevent S. suis infection, investigate its mechanism of anti-S. suis action, and provide further evidence of emodin as an alternative to traditional antibiotic agents.

METHODS

The in vitro anti-S. suis properties of emodin were assessed through minimum inhibitory concentration (MIC) assays, and time-kill assays. Subsequently, the mechanisms underlying emodin's mode of action at the molecular level by targeting FabF were elucidated using molecular docking, site-directed mutagenesis, bio-layer interferometry assays, and cellular thermal shift assays. Finally, metabolomics, cell membrane phospholipid content assay and biochemical parameters assays were used to detect emodin disrupting cell membrane integrity and function by affecting fatty acid biosynthesis.

RESULTS

In this study, we have identified that emodin inhibits S. suis by suppressing free fatty acids (FFAs) synthesis and disrupting phospholipid production by targeting FabF, a key enzyme in the fatty acid biosynthesis pathway. This interference compromises the integrity and functionality of the cell membranes of S. suis. Emodin also triggers the dissipation of the proton motive force, accelerates the tricarboxylic acid cycle, and enhances cellular respiration, ultimately leading to S. suis cell death.

CONCLUSION

This study suggested that emodin inhibits the growth of S. suis via targeting FabF and the inhibition of fatty acid biosynthesis through enzyme-targeted drug design. This represents a novel strategy for developing antimicrobial agents against S. suis and addressing the challenge of antibiotic resistance.

Network toxicological analysis of sodium dehydroacetate in food safety

Sodium dehydroacetate (Na-DHA), a synthetic preservative under tightened regulations, was evaluated for multi-organ toxicity using network toxicology. ADMETlab3.0 predicted genotoxicity, hepatotoxicity, and carcinogenicity risks. Target mining identified 13 cancer-related, 11 liver injury-related, and 8 genotoxicity-related core genes, with shared hubs (ALOX5, PTGS2, SMAD3, TNF) across pathologies. Functional analyses revealed inflammation, oxidative stress, and immune dysregulation as central mechanisms. KEGG pathway analysis linked cancer/liver injury to AGE-RAGE signaling (TNF, NOX4) and genotoxicity to efferocytosis impairment (PTGS2, ALOX5), suggesting DNA repair disruption. The integrated network demonstrated Na-DHA's pleiotropic effects through convergent pathways, transcending organ-specific toxicity. This systemic profile challenges conventional single-endpoint assessments, advocating comprehensive multi-organ risk evaluation.

Sodium dehydroacetate induces porcine oocyte toxicity by inhibiting TCA cycle activity and mitochondrial function, with nicotinamide mononucleotide as a potential protective agent

Sodium dehydroacetate (Na-DHA), a widely used antimicrobial food additive, raises bioaccumulation and organ toxicity concerns, with female reproductive effects remaining understudied. This study investigates Na-DHA's impact on porcine oocyte maturation and evaluates nicotinamide mononucleotide (NMN) as a protective agent. Na-DHA exposure impaired oocyte maturation, suppressing first polar body extrusion and cumulus expansion. Metabolomic analysis revealed disrupted energy metabolism via tricarboxylic acid (TCA) cycle inhibition, notably reducing succinate and fumarate levels. Molecular docking confirmed Na-DHA competitively binds α-ketoglutarate dehydrogenase (α-KGDH), a key TCA enzyme, impairing mitochondrial ATP synthesis and elevating oxidative stress. These metabolic defects induced cytoskeletal abnormalities (spindle disorganization, actin disruption, cortical granule mislocalization), reducing fertilization rates and compromising blastocyst development. NMN supplementation restored mitochondrial function, mitigated oxidative stress and apoptosis, and rescued meiotic progression, enhancing embryonic outcomes. The findings elucidate Na-DHA's reproductive toxicity via α-KGDH-mediated TCA cycle suppression and mitochondrial dysfunction, while demonstrating NMN's protective role through NAD+-dependent metabolic homeostasis. This study highlights Na-DHA's risks to oocyte quality and proposes NMN as a potential therapeutic strategy to counteract food additive-induced reproductive damage.

Stresses in the food chain and their impact on antibiotic resistance of foodborne pathogens: A review

Antibiotic resistance in foodborne pathogens represents a major public health concern. The farm-to-fork continuum is recognized as a critical pathway for the development and spread of this resistance. Throughout the food chain, foodborne pathogens are exposed to diverse environmental stresses, including temperature extremes, osmotic pressure, food additives, and disinfectants, and others. These stress factors can influence antibiotic resistance, with effects varying based on the type and intensity of stress, the pathogen species and strain, and the specific antibiotic involved. Stress conditions can trigger bacterial adaptive responses, such as general stress response systems, the SOS response, and genetic mutations, which can confer cross-protection and enhance antibiotic resistance. Conversely, stress-induced injury or metabolic suppression may increase bacterial susceptibility to certain antibiotics. Understanding these complex interactions is crucial, as suboptimal food processing can inadvertently select for resistant strains. Investigating the molecular mechanisms underlying stress adaptation is essential for developing effective strategies to mitigate antibiotic resistance. Optimizing food processing protocols and implementing robust monitoring systems throughout the food chain are essential steps to reduce these risks. A comprehensive understanding of stress-induced antibiotic resistance will provide a scientific basis for improving food safety and safeguarding global public health.

Heteroarylcyanovinyl Benzimidazoles as New Antibacterial Skeleton with Large Potential To Combat Bacterial Infections

This work developed a class of unique heteroarylcyanovinyl benzimidazoles (HBs) as a new structural skeleton of potential multitargeting antibacterial agents to confront dreadful Staphylococcus aureus infections in the livestock industry. Some target compounds exhibited effective antibacterial activities against the tested strains. Especially, HB 36c with a 5-fluorobenzimidazole ring exerted excellent inhibitory activity toward Staphylococcus aureus ATCC 29213 with a low MIC value of 0.001 mM, being 13-fold more active than norfloxacin. Compound 36c displayed inconspicuous hemolytic rate, low cytotoxicity, and good pharmacokinetics. Moreover, compound 36c could effectively eliminate bacterial biofilms and block the development of resistance, implying its large potential as a drug candidate. Preliminary mechanistic investigations revealed that compound 36c could destroy the bacterial membrane, trigger bacterial oxidative stress, intercalate into DNA, and bind with DNA gyrase B, which showed multitargeting antibacterial potential. These findings suggested that heteroarylcyanovinyl benzimidazoles might provide new promise as potential new structural multitargeting antibacterial agents for the prevention and treatment of Staphylococcus aureus in the livestock industry.

Vitamin B6 resensitizes mcr-carrying Gram-negative bacteria to colistin

Antimicrobial resistance poses a severe threat to human health, with colistin serving as a critical medication in clinical trials against multidrug-resistant Gram-negative bacteria. However, the efficacy of colistin is increasingly compromised due to the rise of MCR-positive bacteria worldwide. Here, we reveal a notable metabolic disparity between mcr-positive and -negative bacteria through transcriptome and metabolomics analysis. Specifically, pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, was significantly diminished in mcr-positive bacteria. Conversely, supplementing with PLP could reverse the metabolic profile of drug-resistant bacteria and effectively restore colistin's bactericidal properties. Mechanistically, PLP was found to augment bacterial proton motive force by inhibiting the Kdp transport system, a bacterial K+ transport ATPase, thereby facilitating the binding of the positively charged colistin to the negatively charged bacterial membrane components. Furthermore, PLP supplementation triggers ferroptosis-like death by accumulating ferrous ions and inducing lipid peroxidation. These two modes of action collectively resensitize mcr-harboring Gram-negative bacteria to colistin therapy. Altogether, our study provides a novel metabolic-driven antibiotic sensitization strategy to tackle antibiotic resistance and identifies a potentially safe antibiotic synergist.

Sex differences in CYP450-based sodium dehydroacetate metabolism and its metabolites in rats

Sodium dehydroacetate (DHA-Na), a widely used preservative, can induce sex-differentiated coagulation disorders primarily resulting from its metabolism. However, the underlying mechanisms remain poorly understood. Here, we identified several Cytochrome P450 (CYP450) sub-enzymes involved in sex differences related to DHA-Na metabolism, along with two related DHA-Na metabolites. CYP1A2, CYP3A2, and CYP2D1 were primarily responsible for DHA-Na metabolism, which was stronger in male rats than in female rats. Inhibition of these isoforms separately resulted in the DHA-Na metabolic capacity in male rats becoming equal to, or even weaker than, that in female rats. Furthermore, Cyp1a2, Cyp3a2, Cyp2d1, and Cyp2c11 expression was higher in male rats than in female rats, suggesting these enzymes are related to exhibited sex differences in DHA-Na metabolism. Moreover, 3-glycoloyl-6-methy-2,3-dihydropyran-2,4-dione (C8H8O5) and 3-imino-6-methyl-2,3-dihydropran-2,4dione (C6H5O3N) were identified as the two main DHA-Na metabolites. These findings provide crucial insights into potential mechanisms underlying sex differences in DHA-Na metabolism and its metabolites in rats.

Reconfiguring the Escherichia coli Electron Transport Chain to Enhance trans-2-Decenoic Acid Production

trans-2-Decenoic acid is a pivotal α,β-medium-chain unsaturated fatty acid that serves as an essential intermediary in the synthesis of 10-hydroxy-2-decenoic acid and various pharmaceutical compounds. Biosynthesis yield of trans-2-decenoic acid by decanoic acid has significantly improved in recent years; however, the oxidative stress of Escherichia coli at high fatty acid concentrations restricts the conversion rate. Here, we introduced a combination of rational design and metabolic rewiring of the E. coli electron transport chain (ETC) to improve trans-2-decenoic acid production. Overexpressing ubiquinone (UbQ) biosynthesis genes enhanced the expression of ETC complex III: UbQ to reduce reactive oxygen species (ROS) accumulation. Furthermore, applying rotenone to inhibit ETC complex I improved the electron transfer efficiency of complex II. The integration of Vitamin B5 and B2 into the fermentation process increased the activities of fatty acyl-CoA synthetase (MaMACS) and fatty acyl-CoA dehydrogenase (PpfadE). Finally, the constructed E. coli BL21(DE3)(ΔfadBJR/pCDFDuet-1-PpfadE-MaMACS/pRSFDuet-1-sumo-CtydiI-ubiI) strain exhibited a 51.50% decrease in ROS and a 93.33% enhancement in trans-2-decenoic acid yield, reaching 1.45 g/L after 66 h, which is the highest yield reported for flask fermentation. This study reports the feasibility of rewiring the ETC regulation and energy metabolism to improve α,β-UCA biosynthesis efficiency.

The Food Additive Benzaldehyde Confers a Broad Antibiotic Tolerance by Modulating Bacterial Metabolism and Inhibiting the Formation of Bacterial Flagella

The rise of antibiotic tolerance in bacteria harboring genetic elements conferring resistance to antibiotics poses an increasing threat to public health. However, the primary factors responsible for the emergence of antibiotic tolerance and the fundamental molecular mechanisms involved remain poorly comprehended. Here, we demonstrate that the commonly utilized food additive Benzaldehyde (BZH) possesses the capacity to induce a significant level of fluoroquinolone tolerance in vitro among resistant Escherichia coli. Our findings from animal models reveal that the pre-administration of BZH results in an ineffective eradication of bacteria through ciprofloxacin treatment, leading to similar survival rates and bacterial loads as observed in the control group. These results strongly indicate that BZH elicits in vivo tolerance. Mechanistic investigations reveal several key factors: BZH inhibits the formation of bacterial flagella and releases proton motive force (PMF), which aids in expelling antibiotics from within cells to reducing their accumulation inside. In addition, BZH suppresses bacterial respiration and inhibits the production of reactive oxygen species (ROS). Moreover, exogenous pyruvate successfully reverses BZH-induced tolerance and restores the effectiveness of antibiotics, highlighting how crucial the pyruvate cycle is in combating antibiotic tolerance. The present findings elucidate the underlying mechanisms of BZH-induced tolerance and highlight potential hazards associated with the utilization of BZH.

Serine synthesis sustains macrophage IL-1β production via NAD+-dependent protein acetylation

Serine metabolism is involved in the fate decisions of immune cells; however, whether and how de novo serine synthesis shapes innate immune cell function remain unknown. Here, we first demonstrated that inflammatory macrophages have high expression of phosphoglycerate dehydrogenase (PHGDH, the rate-limiting enzyme of de novo serine synthesis) via nuclear factor κB signaling. Notably, the pharmacological inhibition or genetic modulation of PHGDH limits macrophage interleukin (IL)-1β production through NAD+ accumulation and subsequent NAD+-dependent SIRT1 and SIRT3 expression and activity. Mechanistically, PHGDH not only sustains IL-1β expression through H3K9/27 acetylation-mediated transcriptional activation of Toll-like receptor 4 but also supports IL-1β maturation via NLRP3-K21/22/24/ASC-K21/22/24 acetylation-mediated activation of the NLRP3 inflammasome. Moreover, mice with myeloid-specific depletion of Phgdh show alleviated inflammatory responses in lipopolysaccharide-induced systemic inflammation. This study reveals a network by which a metabolic enzyme, involved in de novo serine synthesis, mediates post-translational modifications and epigenetic regulation to orchestrate IL-1β production, providing a potential inflammatory disease target.

A Dietary Source of High Level of Fluoroquinolone Tolerance in mcr-Carrying Gram-Negative Bacteria

The emergence of antibiotic tolerance, characterized by the prolonged survival of bacteria following antibiotic exposure, in natural bacterial populations, especially in pathogens carrying antibiotic resistance genes, has been an increasing threat to public health. However, the major causes contributing to the formation of antibiotic tolerance and underlying molecular mechanisms are yet poorly understood. Herein, we show that potassium sorbate (PS), a widely used food additive, triggers a high level of fluoroquinolone tolerance in bacteria carrying mobile colistin resistance gene mcr. Mechanistic studies demonstrate that PS treatment results in the accumulation of intracellular fumarate, which activates bacterial two-component system and decreases the expression level of outer membrane protein OmpF, thereby reducing the uptake of ciprofloxacin. In addition, the supplementation of PS inhibits aerobic respiration, reduces reactive oxygen species production and alleviates DNA damage caused by bactericidal antibiotics. Furthermore, we demonstrate that succinate, an intermediate product of the tricarboxylic acid cycle, overcomes PS-mediated ciprofloxacin tolerance. In multiple animal models, ciprofloxacin treatment displays failure outcomes in PS preadministrated animals, including comparable survival and bacterial loads with the vehicle group. Taken together, our works offer novel mechanistic insights into the development of antibiotic tolerance and uncover potential risks associated with PS use.

Citric Acid Confers Broad Antibiotic Tolerance through Alteration of Bacterial Metabolism and Oxidative Stress

Antibiotic tolerance has become an increasingly serious crisis that has seriously threatened global public health. However, little is known about the exogenous factors that can trigger the development of antibiotic tolerance, both in vivo and in vitro. Herein, we found that the addition of citric acid, which is used in many fields, obviously weakened the bactericidal activity of antibiotics against various bacterial pathogens. This mechanistic study shows that citric acid activated the glyoxylate cycle by inhibiting ATP production in bacteria, reduced cell respiration levels, and inhibited the bacterial tricarboxylic acid cycle (TCA cycle). In addition, citric acid reduced the oxidative stress ability of bacteria, which led to an imbalance in the bacterial oxidation-antioxidant system. These effects together induced the bacteria to produce antibiotic tolerance. Surprisingly, the addition of succinic acid and xanthine could reverse the antibiotic tolerance induced by citric acid in vitro and in animal infection models. In conclusion, these findings provide new insights into the potential risks of citric acid usage and the relationship between antibiotic tolerance and bacterial metabolism.

Response mechanism of microbial community during anaerobic biotransformation of marine toxin domoic acid

Domoic acid (DA) is a potent neurotoxin produced by toxigenic Pseudo-nitzschia blooms and quickly transfers to the benthic anaerobic environment by marine snow particles. DA anaerobic biotransformation is driven by microbial interactions, in which trace amounts of DA can cause physiological stress in marine microorganisms. However, the underlying response mechanisms of microbial community to DA stress remain unclear. In this study, we utilized an anaerobic marine DA-degrading consortium GLY (using glycine as co-substrate) to systematically investigate the global response mechanisms of microbial community during DA anaerobic biotransformation.16S rRNA gene sequencing and metatranscriptomic analyses were applied to measure microbial community structure, function and metabolic responses. Results showed that DA stress markedly changed the composition of main species, with increased levels of Firmicutes and decreased levels of Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria. Several genera of tolerated bacteria (Bacillus and Solibacillus) were increased, while, Stenotrophomonas, Sphingomonas and Acinetobacter were decreased. Metatranscriptomic analyses indicated that DA stimulated the expression of quorum sensing, extracellular polymeric substance (EPS) production, sporulation, membrane transporters, bacterial chemotaxis, flagellar assembly and ribosome protection in community, promoting bacterial adaptation ability under DA stress. Moreover, amino acid metabolism, carbohydrate metabolism and lipid metabolism were modulated during DA anaerobic biotransformation to reduce metabolic burden, increase metabolic demands for EPS production and DA degradation. This study provides the new insights into response of microbial community to DA stress and its potential impact on benthic microorganisms in marine environments.