Pectobacterium carotovorum subsp. carotovorum (Pcc) is the causal agent of bacterial soft rot disease, which triggers rapid decay of infected tomato fruit. Kojic acid, primarily a fermentation metabolite of Aspergillus oryzae, exhibits biocontrol activity against postharvest soft rot of tomato. In this work, we investigated the interference of kojic acid with quorum sensing (QS) in Pcc and elucidated the relevant mechanisms to provide novel theoretical insights into the management of tomato postharvest soft rot. The results demonstrated that kojic acid at a sub-inhibitory concentration (1/4 MIC) markedly suppressed the synthesis of QS signal molecule 3-oxo-C6-HSL in Pcc, as verified by violacein production assays using C. violaceum CV026 and quantitative HPLC assays. Kojic acid downregulated the expression of QS-related genes expI and expR in Pcc. This effect decreased the biosynthesis of 3-oxo-C6-HSL and further inhibited QS signal transduction. Furthermore, molecular docking simulations predicted that kojic acid may share the key residue Ser101 on ExpR with 3-oxo-C6-HSL. Such predicted binding, together with an additional hydrogen bond potentially formed between kojic acid and Asp67 on ExpR, may interfere with QS signal transduction. By interfering with the QS system, kojic acid modulated the expression of the key downstream virulence-related gene pel, impaired bacterial motility, and reduced extracellular polysaccharide production by 41.54%. Meanwhile, kojic acid inhibited biofilm formation of Pcc both in vitro and in tomato wounds. The maximum inhibition rate of biofilm formation reached 36.78% in vitro, while the maximum inhibition rate of biofilm-associated viable cells was 24.10% in tomato wounds. Collectively, these effects attenuated Pcc infectivity for tomato fruit. This study provides a novel approach for mitigating Pcc pathogenicity by targeting its QS system, offering practical value for the postharvest preservation of fruits and vegetables.
Foodborne outbreaks at geographically isolated tourist destinations pose distinctive One Health challenges, combining limited local surveillance capacity, complex intercontinental supply chains, and high visitor turnover. In May 2021, a diarrheal outbreak linked to a gastronomic festival in Fernando de Noronha, that is a remote UNESCO World Heritage island off northeastern Brazil, was attributed to Salmonella enterica serovar Newport ST164. We applied an integrated genomic approach and epidemiological investigation to propose a transmission chain contextualizing and refining case definition of the S. Newport epidemic clone within national and international diversity. Whole-genome sequencing (WGS), SNP-based phylogenomic, pangenome analysis, Salmonella pathogenicity island (SPI) profiling, and resistome characterization was performed on 17 epidemiologically attributed outbreak isolates and 68 contextual genomes from Brazil, France, the United Kingdom, and the United States. The SNP analysis identified a 13 genome clonal core with less than 20 different SNPs demonstrating the possible connection between 9 patient isolates, 2 food isolates, and 2 food handler isolates, consistent with the involvement of colonised kitchen staff in cross-contamination of the ready-to-eat mussel dish. Three poultry isolates in 2020 from a mainland producer, ~2180 km from Fernando de Noronha, differed only 13 to 17 Core-SNPs from the outbreak core, suggesting prior lineage circulation in the supply chain. Pangenome analysis also supports this evidence revealing near-complete genomic overlap of 4544 shared genes within the 5745 gene clusters (99.9%) between outbreak and non-outbreak backgrounds that mostly differentiate by a defense/prophage-associated accessory module. The resistome comprised intrinsic efflux determinants without acquired resistance and showed 35.3% of intermediate ciprofloxacin susceptibility. This One Health based study provides a WGS genomic reconstruction of a S. Newport ST164 outbreak at a remote tourist island, supporting the possibility of circulation from poultry-associated mainland reservoirs and findings consistent with cross-contamination at a gastronomic seafood festival.
Clostridium perfringens is a major foodborne pathogen associated with meat products, yet its dissemination routes and persistence within slaughterhouses remain poorly understood. In this study, whole-genome sequencing combined with multilocus sequence typing (MLST), core genome MLST (cgMLST), and core single nucleotide polymorphism (SNP) analysis was applied to 286 C. perfringens isolates collected from cattle, pig, and poultry slaughterhouses in France. MLST analysis revealed extensive genetic diversity, with most isolates assigned to novel allelic profiles rather than previously described sequence types. Phylogenetic analyses based on cgMLST and SNP data revealed frequent recovery of closely related isolates from feces, meat, surfaces, and air, highlighting widespread dissemination of strains within slaughterhouses during processing. Notably, close genetic related isolates recovered from air and other sample types are consistent with air-associated dissemination within slaughterhouse environments. In addition, the detection of closely related strains across different sampling campaigns suggests the potential persistence of C. perfringens within slaughterhouse environments over time. Most isolates were classified as toxinotype A (97.9%), with a few belonging to toxinotypes D (1.0%) and G (1.0%), and in silico analyses revealed a broad distribution of virulence-associated genes. Antimicrobial resistance genes (ARGs) were commonly detected, particularly those conferring resistance to tetracyclines, although isolates carrying multiple ARGs remained infrequent. Overall, this study provides new insights into the genomic diversity, dissemination pathways, and persistence of C. perfringens in multi-species slaughterhouses. These findings highlight the potential role of air-associated dissemination in contamination dynamics and underscore the importance of improved hygiene control strategies to mitigate food safety risks along the meat production chain.
The study aimed to screen herbal-derived quorum sensing (QS) quenchers and investigate their inhibitory effects on the Serratia liquefaciens S01, a specific spoilage bacterium in smoked chicken legs. Targeting the QS proteins LuxI and LuxR of S. liquefaciens S01, ten compounds were screened as potential QS quenchers by molecular docking. Among these compounds, isoorientin exhibited a relatively low minimum inhibitory concentration (MIC, 250 μg/mL), potent quorum quenching activity, and the strongest binding affinity. In vitro experiments, sub-MIC concentrations of isoorientin significantly inhibited extracellular polysaccharide production, and biofilm formation of S. liquefaciens S01 (P < 0.05). During the storage of smoked chicken legs at 4 °C, the 125 μg/mL isoorientin treatment exhibited significantly lower total viable counts (5.45 log CFU/g) and thiobarbituric acid reactive substances values (1.15 mg/kg) than the other treatments (P < 0.05), and effectively delayed the decline in sensory quality of the smoked chicken legs. This study provides important theoretical insights for delaying meat product spoilage and developing natural QS quenchers.
The global non-alcoholic beer (NAB) market is experiencing unprecedented growth due to a general trend in reduced alcohol consumption. Despite this growth, NABs often do not match their alcoholic counterparts in sensory quality, particularly in aroma complexity and “worty” notes. Yeasts can contribute to aroma not only by producing ethanol, esters, and higher alcohols, but also through biotransformation of bound hop- and malt-derived precursors, releasing low-threshold volatile thiols such as 3-mercaptohexan-1-ol (3MH), 3-sulfanyl-4-methylpentan-1-ol (3S4MP) and 4-mercapto-4-methylpentan-2-one (4MMP), which can impart tropical, guava, grapefruit and blackcurrant notes. Here, we screened 86 yeasts, including non-Saccharomyces species, via a multi-step screening strategy combining micro fermentation-based assessment of maltose utilisation, inability to produce volatile phenolic off-flavours via decarboxylation, biotransformation potential (assessed qualitatively via growth on cysteine as sole nitrogen source, indicative of β-lyase activity), and aromatic potential. Nine strains meeting these criteria were applied in wort fermentation trials. Strain selection to pilot-scale trials was determined by sensory analysis and chemical analysis, including direct quantification of thiol release via GC–MS/QQQ. Of these, Pichia membranifaciens and Saccharomycodes ludwigii were identified as most suitable for non-alcoholic IPA-style beer production, exhibiting enhanced fruity and floral aromas relative to a commercial maltose-negative Saccharomyces cerevisiae strain. In two pilot-scale trials using different hop varieties, and in one trial with the addition of thiol precursors, GC–MS/QQQ analyses combined with sensory evaluation showed that yeast strain selection and precursor supplementation both enhanced hop-derived aroma expression, particularly when dry hopping during active fermentation. Direct quantification confirmed that precursor supplementation increased the wort bound-thiol precursor concentration up to 2.3-fold, supporting precursor availability as a key driver of thiol release. These findings demonstrate that targeted, low-cost micro fermentation-based yeast screening, combined with hop and precursor management, provides a practical route to producing aromatic, hop-forward non-alcoholic beers with enhanced tropical and fruity character.
Salmonella Enteritidis (S. Enteritidis) is a primary foodborne pathogen whose stress resistance raises major food safety concerns. Clove essential oil (CEO), a natural antimicrobial agent, has garnered considerable attention due to its broad-spectrum antibacterial activity. However, the molecular mechanisms responsible for its antibacterial effect remain poorly elucidated. In this work, an integrated strategy combining proteomic profiling, bioinformatic analysis, and mutant analysis was adopted to explore the antibacterial mechanism of CEO against S. Enteritidis. The results showed that the minimum inhibitory and bactericidal concentrations of CEO were 2 g/L and 4 g/L, respectively. Proteomic and bioinformatic analyses revealed that CEO modulated the expression of 1437 proteins involved in cellular metabolism, ABC transporters, two-component systems, global regulation, flagellar assembly, and other cellular processes. Based on the proteomics results, three proteins from these pathways (HiuH, ProX, and PmrA) were selected for further investigation. The functional relevance of these proteins was subsequently validated by phenotypic comparisons between gene knockout mutants and the wild-type strain under CEO treatment. Intriguingly, the ΔhiuH, ΔproX, and ΔpmrA mutants displayed better in vitro growth yet greater susceptibility to CEO inactivation in chicken meat, highlighting the importance of assessing CEO efficacy in food matrices. Collectively, this work reveals the multi-pathway response of S. Enteritidis to CEO exposure, offering new mechanistic insights into the interplay between bacterial stress-defense systems and essential oil-mediated bacterial inactivation.
Bacterial competition is a major factor influencing microbiota succession in fish. However, the competition mechanisms among dominant spoilage bacteria in grass carp remain to be systematically investigated. Therefore, this study aimed to elucidate the mutual competition relationships and mechanisms among five representative spoilage bacteria isolated from grass carp. To this end, we constructed synthetic microbial communities (SynComs) with these five strains and employed metatranscriptomics coupled with phenotypic verification to demonstrate their interactions at both transcriptional and phenotypic levels. The results showed that bacterial competitiveness largely determined the microbiota composition in SynComs. Aeromonas rivipollensis ranked the most competitive bacterium by both inhibiting the virulence phenotypes (siderophore production, biofilm, and swimming motility) and disrupting the carbohydrate/amino acid metabolisms of Shewanella putrefaciens and Pseudomonas putida. Concurrently, A. rivipollensis enhanced its own siderophore production and motility when interacting with these competitors, which further promoted its advantage. In contrast, S. putrefaciens was the second most competitive, as it potently utilized amino acids and enhanced its siderophore production and motility in response to P. putida. Collectively, this study reveals that bacterial competition in fish is mediated by both phenotype interference and metabolism disruption, suggests siderophore as a new target for controlling microbiota succession and quality deterioration in fish, and therefore provides theoretical guidance for developing new fish preservation strategies.
Our previous study demonstrated that L-phenylalanine (L-Phe) can induce enhanced biocontrol efficacy of Yarrowia lipolytica against postharvest blue mold in pear fruit. This work also clarified the physiological mechanisms underlying the L-Phe–mediated improvement in biocontrol performance; however, the detailed molecular mechanisms responsible for this enhancement require further investigation. Results showed that Y. lipolytica cultured with 5 mmol/L L-Phe significantly reduced decay incidence in pear fruit without adversely affecting postharvest quality. In addition, L-Phe induction increased the production of volatile organic compounds by Y. lipolytica, effectively inhibiting the mycelial growth of Penicillium expansum. During storage, L-Phe treatment enhanced the oxidative stress tolerance of Y. lipolytica by alleviating ROS accumulation in yeast cells at fruit wound sites, which promoted better colonization of Y. lipolytica in wounds. Furthermore, L-Phe induction increased the activities of chitinase (CHI) and β-1,3-glucanase (GLU) in Y. lipolytica, indicating enhanced cell wall metabolic activity. Transcriptome analysis revealed significant metabolic reprogramming in L-Phe–treated cells, with key pathways, including propanoate metabolism, glycerolipid metabolism, lysine degradation, butanoate metabolism, and tryptophan metabolism, being significantly upregulated. These changes improved both oxidative stress adaptation and energy utilization efficiency in the yeast. Overall, L-Phe induction effectively enhances the biocontrol capacity of Y. lipolytica, providing new insights into improving the performance of antagonistic microorganisms in postharvest disease control.
Mulberry leaf extract (MLE) is rich in bioactive compounds with potent hypoglycemic activity, but is constrained by its sensory drawbacks. In this study, Aspergillus chevalieri CTCF-AC-1, isolated from Fu brick tea, was employed to ferment MLE for improving both its flavor profile and functional efficacy. Fermentation dynamically remodeled MLE composition: total phenolic acids decreased from 859.8 to 566.5 mg/mL, while total amino acid content increased dramatically from 322.13 mg/mL to 570.31 mg/mL with methionine and cysteine increased by 111.5-fold and 5.4-fold, respectively. The content of 1-deoxynojirimycin (1-DNJ) remained stable (0.27–0.29 mg/g). Headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) analysis identified 62 volatile compounds, revealing a reduction in bitter/astringent notes (2,3,5-trimethylpyrazine, butyric acid, etc.) and an increase in compounds associated with fruity and sweet aromas (d-3-hexanone, 2,3-dimethylpyrazine etc.). Furthermore, the fermented MLE (FMLE) exhibited significantly enhanced in vitro antioxidant activity and inhibitory effects on α-amylase and α-glucosidase. In a zebrafish hyperglycemia model, FMLE showed lower acute toxicity (LC1 = 1109 μg/mL vs. 609 μg/mL for MLE) and superior efficacy in promoting pancreatic glucose uptake in a dose-dependent manner. Transcriptomic and QPCR analyses elucidated that FMLE's hypoglycemic mechanism involves regulation of key genes (fut9d, irg1l, mmp9, gck) implicated in glucose metabolism and immune response. These findings demonstrate that fermentation with A. chevalieri effectively alleviates the sensory limitations of MLE while enhancing its hypoglycemic potency and biocompatibility, providing a scientific basis for its use in functional foods and nutraceuticals.
This study evaluated the effects of co-inoculating Pichia kluyveri CCMA0237 and Hanseniaspora uvarum CCMA0236 during cocoa fermentation with the SJ02 hybrid on the chemical profiling and sensory quality of chocolate. We monitored microbial dynamics using qPCR, chemical analyses by HPLC, LC/MS, and GC/MS, and sensory analysis using an acceptance test followed by CATA questions. The co-inoculated yeasts showed higher microbial density; H. uvarum reached the highest cell density, while P. kluyveri in the control was detected only at 72 h at a low concentration. Co-inoculation accelerated sugar metabolism, resulting in higher ethanol accumulation in the pulp. In the control, seeds showed higher acetic acid levels at 72 h. Methylxanthines showed higher levels in the control at the end of drying. Free amino acids increased at 144 h, especially in co-inoculation, with increases of 35.5% in total and 68.7% in essential ones. Chemical characterization revealed broader, more intense formation of key volatiles, particularly higher alcohols and ketones. Sensory evaluation supported these findings, with chocolates from co-inoculated fermentations showing stronger cocoa notes and reduced bitterness. These results demonstrate that targeted co-inoculation with P. kluyveri CCMA0237 and H. uvarum CCMA0236 enhances the chemical complexity and sensory quality of cocoa hybrid SJ02, offering a strategy to improve chocolate value.
Multidrug-resistant (MDR) Escherichia coli from agricultural environments is an emerging threat to food safety and public health. Bacteriophages have emerged as promising alternatives to antibiotics for controlling MDR bacteria. However, studies evaluating phage biocontrol against phenotypically characterized MDR E. coli isolates from agricultural environments remain limited. This study aimed to characterize E. coli isolates recovered from agricultural environments and to develop and evaluate a phage cocktail against a target MDR isolate. A total of 11 E. coli strains were isolated and assessed for antibiotic susceptibility, biofilm formation, and swimming motility. Among them, KAE09 was selected as the target MDR isolate based on its resistance to multiple antibiotics, including streptomycin, tetracycline, oxolinic acid, and ciprofloxacin, together with strong biofilm-forming ability and high motility. To control this isolate, we developed a phage cocktail consisting of two E. coli phages, ELP2 and ELT3, with previously reported distinct receptor specificities. Cross-resistance analysis showed no reciprocal cross-resistance between ELP2 and ELT3 in KAE09. The phage cocktail significantly inhibited bacterial growth, reduced preformed biofilms, and suppressed biofilm formation of KAE09. The cocktail also effectively reduced viable cell counts of the isolate on lettuce at room temperature and under refrigeration. These findings highlight the potential of the phage cocktail as an effective biocontrol agent for reducing MDR E. coli contamination on fresh produce.
Diarrheagenic Escherichia coli (DEC) remains an important foodborne pathogen, yet long-term comparative genomic surveillance data jointly characterizing food-derived and patient-derived isolates remain limited. This surveillance-based comparative study integrated antimicrobial susceptibility testing and whole-genome sequencing to characterize diarrheagenic Escherichia coli isolates recovered from food and patient sources in Lishui, Southeast China, during 2018-2025, with emphasis on occurrence, resistance profiles, genomic backgrounds, and plasmid replicon-associated features. Antimicrobial susceptibility testing was performed for 258 selected isolates, and whole-genome sequencing was conducted for a curated analytical subset of 204 isolates. The sequenced subset was used for diversity-oriented comparative genomic analysis rather than for unbiased prevalence estimation of the entire DEC collection. EAEC predominated in both sources, although food-associated occurrence was heterogeneous across categories, with the highest recovery rate observed in raw meat. Patient-derived isolates showed a broader overall resistance burden, whereas food-derived isolates retained substantial resistance to tetracycline, chloramphenicol, and florfenicol. Phylogenetic analysis showed partial overlap in genomic backgrounds between food-derived and patient-derived isolates, while representative resistance determinants displayed both broadly distributed and lineage-enriched patterns. Replicon-based plasmid profiling identified 42 plasmid types, including 12 detected in both sources, with IncF-related replicons predominating among these shared profiles. Several food-derived isolates carried multiple plasmid replicon types that were also observed in patient-derived isolates. Overall, food-derived and patient-derived DEC showed partial overlap in genomic backgrounds, resistance determinants, and replicon-defined plasmid profiles within this surveillance setting, while retaining source-associated heterogeneity. These findings should be interpreted as surveillance-based comparative evidence rather than as evidence of direct source attribution or transmission.
Pseudomonas has been identified as the dominant spoilage genus in aerobically stored bighead carp eye muscle. However, the specific roles of individual strains and their potential interactions in protein degradation have not been fully elucidated. In this study, 56 strains of spoilage bacteria were isolated and identified from the eye muscle after 10 days of chilled storage at 4 °C. After in vitro hydrolytic activity screening, Pseudomonas fragi (PF), Pseudomonas psychrophila (PP), and their mixture (Mix) were used to inoculate sterile eye muscle in situ. Differences among the three treatment groups were evaluated using a series of indicators, including SDS-PAGE, TCA-soluble peptides, free amino acids, biogenic amines, TVB-N, peptidomics, transmission electron microscopy, and color analysis. Results showed that PF exhibited the lowest histidine level (161.14 μg/g muscle) and the highest histamine level (0.26 mg/kg) after storage. PP, PF, and Mix all induced higher degradation of the myosin heavy chain, with Mix showing the highest degradation degree of 10,231.3 × 105. PF preferentially degraded desmin, titin, nebulin, and myosin, whereas PP targeted myozenin, myomesin, MyBPC/MyBPH, and tropomodulin. Mix exhibited higher degradation of troponin, CapZ, myosin light chain, and actin. Meanwhile, Mix showed the most severe myofibrillar damage and had the lowest a⁎ value after storage. In conclusion, P. fragi and P. psychrophila exhibited distinct protein degradation behaviors, and their interaction accelerated protein degradation and quality deterioration in the eye muscle of bighead carp during storage.
Ready-to-eat fresh fruits sold in informal urban settings in West Africa are highly susceptible to microbial contamination because of poor hygiene and uncontrolled storage conditions. This study assessed the microbiological quality of street-vended sliced papaya (Carica papaya) in urban Benin and estimated the associated Salmonella infection risk using quantitative microbial risk assessment (QMRA). Hygienic practices were documented among 135 vendors, while consumption data were collected from 437 informants. A total of 135 papaya samples were collected from street vendors in three major cities of Benin, namely Abomey-Calavi, Cotonou, and Porto-Novo. The samples were analyzed for total viable counts, Escherichia coli, fecal coliforms, coagulase-positive staphylococci (CPS), and Salmonella spp. Poor hygiene practices, namely the use of non-potable water, inadequate utensil sanitation, bare-hand handling, and prolonged ambient storage (up to 16 h at ca. 30 °C), were common. High contamination levels were observed: E. coli was detected in 75.6% of samples (3.4 log CFU/g), fecal coliforms reached 6 log CFU/g, and CPS was detected in all samples (5.5 log CFU/g). Salmonella spp. was confirmed in 3% (4/135) of samples. QMRA estimated a median daily probability of Salmonella infection (P50) of 1.33E-03 during the high availability period of papaya, with 90% of simulated outcomes ranging from 5.47E-05 to 2.90E-02 (P5-P95). The P50 estimate corresponded to an annual burden of 244,370 cases per million consumers. Lower risk levels were estimated during the low availability period. A scenario analysis indicated that continuous refrigerated storage during vending could reduce the infection risk by 91.1%. These findings highlight the value of combining field microbiological data with probabilistic risk assessment to guide context-specific food safety interventions in the region.
Enterococci from animal-derived foods are key reservoirs for antimicrobial resistance (AMR) in the food chain. However, comparative genomic studies investigating the distribution of the oxazolidinone resistance gene optrA among food- and human-derived Enterococci remain limited. This study assessed linezolid-resistant Enterococci from retail meat and healthy humans in Beijing, China (2023-2024). Among 87 isolates, E. faecalis and E. faecium predominated. Food-derived isolates showed broader resistance profiles than human isolates. Fourteen optrA-positive strains were identified, accounting for 92.9% of food isolates. optrA frequently co-localized with erm(A), ant(9)-Ia, and fexA on Tn554-family transposons, suggesting a potentially transferable multidrug resistance module. Notably, an optrA-positive E. faecalis ST699 clone was identified for the first time in Chinese retail meat. This clone formed a distinct lineage and carried a complete Tn554-optrA island. A representative ST699 isolate exhibited enhanced fitness and virulence potential in the Galleria mellonella model. These findings highlight animal-derived foods as important reservoirs of linezolid-resistant Enterococci and provide genomic evidence consistent with their role as potential sources of optrA-mediated resistance. The emergence of a multidrug-resistant E. faecalis ST699 clone with enhanced fitness characteristics underscores the need for continued surveillance of foodborne antimicrobial resistance within the One Health framework.
Brettanomyces bruxellensis is a major spoilage yeast in winemaking due to its persistence in winery environments and its ability to produce volatile phenols responsible for sensory defects. This study evaluated the biocontrol potential of selected Metschnikowia pulcherrima strains, focusing on the role of pulcherriminic acid production and its application in winery-relevant conditions. Twelve M. pulcherrima strains were screened for pulcherriminic acid production under different iron conditions, revealing strong strain-dependent variability. Three strains (1521, 1558, and DSM 70336) were identified as the most efficient producers and exhibited significant iron depletion capacity. The produced metabolite remained stable over an 18-day period. Cell-free supernatants from selected strains inhibited the growth of B. bruxellensis in a strain- and concentration-dependent manner, with the strongest effect observed for strain M. pulcherrima DSM 70742. Biofilm assays on oak wood demonstrated that the supernatants reduced viable cell counts by up to 80-86% when applied at the initial stage of colonization, whereas significantly lower reductions (10-55%) were observed for pre-established biofilms. Application of a mixed supernatant under winery conditions successfully prevented Brettanomyces contamination in treated barrels without affecting wine sensory properties. These findings indicate that M. pulcherrima-derived metabolites primarily act by limiting iron availability and interfering with early biofilm formation. The results highlight the potential of M. pulcherrima as a practical and sustainable biocontrol agent for reducing spoilage yeast contamination and limiting the need for chemical preservatives in winemaking.
The escalating global threat of multidrug resistant (MDR) Salmonella, a foodborne pathogen with animal-derived foods serving as the primary transmission vehicle, underscores the urgent need for effective lytic phages for biocontrol. From 142 environmental and farm samples in Shandong Province, we isolated 103 phages active against MDR S. Enteritidis and S. Typhimurium, which were the most prevalent Salmonella serovars in China. Two Siphoviridae phages vB-SenS-S1 and vB-SenS-SEC2 were selected for further study. With optimal multiplicities of infection (MOIs) of 10-2 (vB-SenS-S1) and 10-5 (vB-SenS-SEC2), both phages exhibited a 20 min latent period, yielding burst sizes of 52 and 37 PFU/cell, respectively. They also demonstrated stability across a range of temperatures (50-60 °C), pH levels (5-11), and after 1 h of UV exposure. Genomic analysis identified vB-SenS-S1 (43,002 bp, 47.04% GC) and vB-SenS-SEC2 (42,948 bp, 47.65% GC) as novel double-stranded DNA phages. Functional annotation confirmed the presence of genes essential for structural assembly, host lysis, and DNA replication/metabolism, and also verified the absence of resistance, virulence, and lysogeny-associated genes. Both phages vB-SenS-S1 and vB-SenS-SEC2 exhibited synergy with colistin and tetracycline. The synergy with colistin was particularly potent, leading to complete bacterial eradication in vitro. The in vivo therapeutic efficacy was further validated in both Galleria mellonella larvae and murine models of MDR Salmonella infection. Combination therapy with vB-SenS-SEC2 and colistin not only dramatically increased survival but also achieved a significant reduction in bacterial burden across multiple visceral organs of infected mice. Moreover, vB-SenS-S1 (108 PFU/mL) completely inhibited MDR Salmonella on chicken meat at 4 °C and -20 °C when initial contamination was ≤103 CFU/mL. This study not only expands the diversity of Salmonella phages but also highlights their potential as biocontrol agents in both clinical veterinary use and food decontamination, thereby enhancing food quality and safety at both the meat production source and the terminal product.
Density dependence is a key characteristic of quorum sensing (QS) in fungi; however, no relevant reports have been found in Monascus. Therefore, this study aimed to investigate the effects of initial spore density on the morphological development and polyketide secondary metabolism of Monascus purpureus to elucidate the regulatory role of QS. At the high initial spore density, more active conidial development and secondary metabolism were observed in the early fermentation stage, accompanied by rougher hyphal surfaces, increased secretion and larger vacuoles. Gene set enrichment analysis (GSEA) based on transcriptomic data revealed that high initial spore density activated ribosome biosynthesis to support rapid cell growth and secondary metabolism, whereas low initial spore density upregulated genes associated with peroxisome biosynthesis, the enzymatic antioxidant system, fatty acid degradation, fatty acid biosynthesis, and asexual sporulation. Furthermore, the reduction in linoleic acid content at high initial spore density suggested that linoleic acid and its derivatives may function as putative quorum sensing molecules (QSMs). Finally, a potential regulatory network integrating initial spore density with secondary metabolism and development was proposed. These findings enhance the understanding of the QS network in Monascus and offer a theoretical basis for the optimization of fermentation processes.
Postharvest blue mold in apples caused by Penicillium expansum poses a great risk to food safety. Here, we report on a phytopathogen targeted enrichment strategy that led to the isolation of an endophytic biocontrol agent (BCA), Bacillus subtilis 507, with strong antagonism against P. expansum. Using a unique dual application approach that combines both live BCA and its crude metabolites (Bac + CM), our result showed an enhanced efficacy. Relative to the control, the disease incidence of blue mold in apples was reduced by 45.95% and lesion diameter was limited to 19.18 mm. Untargeted metabolomics identified bioactive compounds, including 3-phenyllactic acid, pipecolic acid, and spermine, suggesting direct antifungal activity and host based modulation. The mechanistic investigations showed that Bac + CM inhibited spore germination up to 37.3%, and depletion of ergosterol with 97.09% cellular membrane leakage. Fungal hyphal deformation and structural collapse were confirmed by SEM. The BCA rapidly colonized apple fruit wounds and surfaces up to 9.4 log10CFU and reduced natural decay to 5.13% without affecting fruit quality. This study presents a combined, metabolite-enhanced biocontrol strategy that positions B. subtilis 507 as a promising candidate for sustainable management of postharvest food diseases such as blue mold in apples.
High dietary sodium in fermented foods like traditional Chinese paocai poses significant public health risks and environmental burdens. As a preventative control measure, partial NaCl substitution with KCl and MgCl2 is explored, but its complex impact on flavor and microbial mechanisms remains unclear. This multi-omics study investigated the ion-specific effects of sodium salt substitution with 30% KCl (K30), 30% MgCl2 (Mg30), and a combination of 15% KCl and 15% MgCl2 (KMg15) on the fermentation of radish paocai by Levilactobacillus brevis PL6-1. All low-sodium groups maintained comparable LAB growth, acidification, and overall acceptability, ensuring microbiological safety and stability. The 30% MgCl2 substitution significantly reduced radish hardness, while K+ promoted mannitol synthesis and influenced citric acid metabolism. Combined K+/Mg2+ substitution (KMg15) further increased the fruity compound ethyl propanoate. Transcriptomic analysis revealed targeted gene expression changes in L. brevis PL6-1, rather than widespread alterations, in response to specific ionic environments. Key genes involved in propanediol utilization, hexuronic acid degradation, and stress response were differentially expressed. Notably, the upregulation of the pduE gene may have contributed to the increase in ethyl propanoate content. Functional enrichment showed Mg2+ stimulated broader energy metabolism, increasing metabolic diversity. This research elucidates how specific cations modulate gene expression in L. brevis, shaping distinct flavor profiles. Findings provide a scientific basis for designing innovative, low-sodium fermented vegetables with tailored sensory attributes, enhancing food quality and product sensory quality through effective preventative control measures.
