Propionate and Butyrate Inhibit Biofilm Formation of Salmonella Typhimurium Grown in Laboratory Media and Food Models

Antibiofilm efficacies and mechanism of perillaldehyde against Shewanella putrefaciens

Shewanella putrefaciens is Gram-negative bacterium and important spoilage organism in aquatic products, negatively impacting the organoleptic properties of aquatic products. S. putrefaciens could form biofilm, which increases persistence and contamination in food system. Efficient antibiofilm strategies are urgently needed to reduce its presence in food environment. This study aimed to explore the impact of perillaldehyde on S. putrefaciens biofilm and the underlying mechanisms using transcriptomic analysis. Perillaldehyde remarkably reduced extracellular polymeric substance contents, inhibited metabolic activity of biofilm cells, disrupted bacterial motility, loose biofilm structure and decreased biofilm formation in food juice and on various surfaces (stainless steel, silicone, glass, razon clam and shrimp). Transcriptome analysis revealed that 553 differentially expressed genes were identified, among which 254 were down-regulated and 299 were up-regulated. The differentially expressed genes included ATP-binding cassette transporters, ribosome, two-component systems, resistance/nodulation/division efflux systems, quorum sensing, amino acid metabolism, biosynthesis and degradation pathways. The findings demonstrate antibiofilm properties of perillaldehyde against S. putrefaciens and indicate that perillaldehyde could be developed as an antibiofilm agent to mitigate existence and contamination of S. putrefaciens and to reduce associated food loss caused by this spoilage bacteria.

Propionate serves as a degradable control agent of citrus canker by acidifying cytoplasm and depleting intracellular ATP in Xanthomonas citri

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to global citrus production. Current disease control relies on the widespread application of copper-based bactericides. However, the excessive and recurrent use of copper has resulted in adverse outcomes, such as the emergence of copper-resistant strains and detrimental impacts on both the environment and human health. In this study, we demonstrate that propionate effectively inhibits the growth of Xanthomonas citri and is degradable by soil microbes, making it a promising and economic alternative for citrus canker management. Propionate exerts pleiotropic effects on Xcc by disrupting membrane potential, motility, and the type III secretion system. It acts as a bacteriostatic agent by acidifying the bacterial cytoplasm and disrupting proton homeostasis, which depletes intracellular ATP and induces cell dormancy. Through a Tn5 mutant library screen, we identified a propionate-sensitive mutant with a disrupted prpC gene, part of the prp operon, which is involved in propionate metabolism and regulated by PrpR. PrpR represses the prp operon by binding to a palindromic motif in the prpB promoter region. Our findings highlight propionate as a favorable control agent for citrus bacterial canker, offering effective disease management while mitigating the environmental and health concerns associated with copper-based treatments.IMPORTANCECitrus canker severely impacts citrus production, threatening a major fruit industry. Traditionally, managing this disease has depended on copper-based bactericides, which bring significant downsides, including copper resistance in pathogens and environmental toxicity. This study identifies propionate as a promising alternative to copper treatments for combating citrus canker caused by Xanthomonas citri subsp. citri. Propionate offers a dual benefit: it disrupts essential bacterial functions, effectively controlling the pathogen, and it is biodegradable in soil, which reduces environmental impact. Our findings show that propionate acidifies cytoplasm and disrupts critical bacterial processes such as membrane potential and motility, while depleting intracellular ATP and inducing cell dormancy. Propionate, therefore, emerges as an eco-friendly, cost-effective option for sustainable management of citrus bacterial canker, addressing both agricultural and environmental challenges in citrus production.

Caffeine as a natural inhibitor of Salmonella biofilms in fruit juices

Caffeine holds promise for applications in food safety due to its antioxidant and antibacterial properties. Given rising antimicrobial resistance, its natural antimicrobial potential is valuable for controlling foodborne pathogens and reducing reliance on synthetic preservatives. This study aimed to explore caffeine as an alternative to control Salmonella biofilms in fruit juice substrates. Salmonella Enteritidis and S. Typhimurium biofilm were developed in brain heart infusion (BHI) broth (control) and grape and apple juice before and after caffeine application. Biofilm inhibition was quantified by crystal violet staining, exopolysaccharide (EPS) production, and visualization through confocal and scanning electron microscopy. Swimming motility assays assessed caffeine's impact on bacterial motility. Both strains formed biofilms in the tested juices. The minimum inhibitory concentration (MIC) of caffeine was 9.37 mM mL-1 for S. Typhimurium and 18.75 mM mL-1 for S. Enteritidis. Biofilm inhibition was observed for treatments before and after caffeine application, with varying levels depending on the matrix. EPS production and inhibition were higher in biofilms formed in grape and apple juices compared to the control (BHI). Sub-inhibitory concentrations of caffeine reduced motility in both strains. These findings suggest that caffeine may be a promising approach to control Salmonella biofilms in the food industry.

Dietary limonin alleviates Salmonella Typhimurium-induced colitis via dual targeting virulence SopB and SopE2 and inhibiting RAC1/CDC42/Arp2/3 pathway and regulating gut microbiota

Salmonella enterica serovar Typhimurium (STM) causes severe colitis, necessitating the development of effective drugs. Here, the dockings of limonin with the STM T3SS-1 virulence factor SopB or SopE2 showed strong binding activity in silico and was verified by CETSA and DARTS assays in vitro. Limonin inhibited the enzyme activities and expression of SopB and SopE2 in vitro. Furthermore, we found that limonin treatment significantly reduced the number of STM colony-forming units (CFUs) in infected HeLa and Raw264.7 cells, which resulted in a decrease in the rate of membrane ruffling mediated by SopB-regulated Arf6/Cyth2/Arf1-, RAC1-, and CDC42-driven Arp2/3-dependent actin polymerization and the SopE2-regulated CDC42/Arp2/3 pathway, and the confocal laser scanning microscopy analysis revealed that limonin treatment repressed the recruitment of the Salmonella-containing vacuole (SCV) biomarkers LC3, Rab7, GAL8 and NDP52. Furthermore, limonin treatment ameliorated STM-induced colitis by reducing the disease activity index (DAI), colon shortening, and MPO and EPO activities; mitigating the severity of S. Typhimurium-induced colitis damage; and influencing the levels of inflammatory factors (IL-1β, IL-6, IL-10, TNF-α and IFN-γ) while increasing the levels of colonic epithelial barrier and tight junction genes (Mucin 1, Mucin 2, Occludin, Claudin-3 and ZO-1). A gut microbiota analysis revealed that limonin treatment influenced α- and β-diversity of the flora and increased the counts of the beneficial bacteria Muribaculum and Faecalibaculum to regulate gut microbiota dysbiosis. Finally, colon SCFA measurements revealed that limonin treatment significantly increased acetate, butyrate, propionate and valerate concentrations. Thus, this study is an important reference for the anti-STM effects of limonin on induced colitis.

Differences in Biofilm Formation of Listeria monocytogenes and Their Effects on Virulence and Drug Resistance of Different Strains

Listeria monocytogenes is recognized as one of the primary pathogens responsible for foodborne illnesses. The ability of L. monocytogenes to form biofilms notably increases its resistance to antibiotics such as ampicillin and tetracycline, making it exceedingly difficult to eradicate. Residual bacteria within the processing environment can contaminate food products, thereby posing a significant risk to public health. In this study, we used crystal violet staining to assess the biofilm-forming capacity of seven L. monocytogenes strains and identified ATCC 19112 as the strain with the most potent biofilm-forming. Subsequent fluorescence microscopy observations revealed that the biofilm-forming capacity was markedly enhanced after two days of culture. Then, we investigated into the factors contributing to biofilm formation and demonstrated that strains with more robust extracellular polymer secretion and self-agglutination capabilities exhibited a more pronounced ability to form biofilms. No significant correlation was found between surface hydrophobicity and biofilm formation capability. In addition, we found that after biofilm formation, the adhesion and invasion of cells were enhanced and drug resistance increased. Therefore, we hypothesized that the formation of biofilm makes L. monocytogenes more virulent and more difficult to remove by antibiotics. Lastly, utilizing RT-PCR, we detected the expression levels of genes associated with biofilm formation, including those involved in quorum sensing (QS), flagellar synthesis, and extracellular polymer production. These genes were significantly upregulated after biofilm formation. These findings underscore the critical relationship between extracellular polymers, self-agglutination abilities, and biofilm formation. In conclusion, the establishment of biofilms not only enhances L. monocytogenes' capacity for cell invasion and adhesion but also significantly increases its resistance to drugs, presenting a substantial threat to food safety.

Anti-biofilm mechanism of a synthetical low molecular weight poly-d-mannose on Salmonella Typhimurium

In this study, a low molecular weight poly-d-mannose (LMWM) was separated from a mixed polysaccharide synthesized previously. Monosaccharide composition, Fourier-Transform infrared spectroscopy (FT-IR), periodate oxidation and smith degradation were determined. After safety evaluation, the inhibition of LMWM on the different biofilm formation stages of Salmonella enterica serovar Typhimurium (S. Typhimurium) was tested in vitro. Furthermore, the effect of LMWM on the adhesion of S. Typhimurium to Caco-2 cells and cell surface hydrophobicity (CSH) were observed. Results indicated that LMWM was a homopolysaccharide without cytotoxicity and hemolysis, containing both α-mannose and β-mannose. It showed obvious anti-biofilm activity on S. Typhimurium and mainly activated on the initial adhesion and formation stage, even better than the commercial S. cerevisiae mannan (CM). LMWM inhibited the adhesion of S. Typhimurium on Caco-2 cells with the inhibition rate of 61.04 % at 2 mg/ml. Meanwhile, LMWM decreased the hydrophobicity of S. Typhimurium cell surface. In conclusion, the inhibitory effect on S. Typhimurium biofilm was not caused by bacteriostatic or bactericidal activity of LMWM. The specific anti-adhesion and the decrease of bacterial CSH by LMWM may closely relate to anti-biofilm mechanism. This study provides some supports for the application of LMWM as antibiotics alternative on S. Typhimurium in the future.

Gut microbiome derived short chain fatty acids: Promising strategies in necrotising enterocolitis

Necrotising enterocolitis (NEC) is a devastating condition that poses a significant risk of morbidity and mortality, particularly among preterm babies. Extensive research efforts have been directed at identifying optimal treatment and diagnostic strategies but results from such studies remain unclear and controversial. Among the most promising candidates are prebiotics, probiotics and their metabolites, including short chain fatty acids (SCFAs). Such metabolites have been widely explored as possible biomarkers of gut health for different clinical conditions, with overall positive effects on the host observed. This review aims to describe the role of gut microbiome derived SCFAs in necrotising enterocolitis. Until now, information has been conflicting, with the primary focus on the main three SCFAs (acetic acid, propionic acid, and butyric acid). While numerous studies have indicated the relationship between SCFAs and NEC, the current evidence is insufficient to draw definitive conclusions about the use of these metabolites as NEC biomarkers or their potential in treatment strategies. Ongoing research in this area will help enhance both our understanding of SCFAs as valuable indicators of NEC and their practical application in clinical settings.

Butyrate affects bacterial virulence: a new perspective on preventing enteric bacterial pathogen invasion

Enteric bacterial pathogens are a major threat to intestinal health. With the widespread use of antibiotics, bacterial resistance has become a problem, and there is an urgent need for a new treatment to reduce dependence on antibiotics. Butyrate can control enteric bacterial pathogens by regulating the expression of their virulence genes, promoting the posttranslational modification of their proteins, maintaining an anaerobic environment, regulating the host immune system and strengthening the intestinal mucosal barrier. Here, this review describes the mechanisms by which butyrate regulates the pathogenicity of enteric bacterial pathogens from various perspectives and discusses the prospects and limitations of butyrate as a new option for the control of pathogenic bacteria.

Therapeutic Approach Targeting Gut Microbiome in Gastrointestinal Infectious Diseases

While emerging evidence highlights the significance of gut microbiome in gastrointestinal infectious diseases, treatments like Fecal Microbiota Transplantation (FMT) and probiotics are gaining popularity, especially for diarrhea patients. However, the specific role of the gut microbiome in different gastrointestinal infectious diseases remains uncertain. There is no consensus on whether gut modulation therapy is universally effective for all such infections. In this comprehensive review, we examine recent developments of the gut microbiome's involvement in several gastrointestinal infectious diseases, including infection of Helicobacter pylori, Clostridium difficile, Vibrio cholerae, enteric viruses, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa Staphylococcus aureus, Candida albicans, and Giardia duodenalis. We have also incorporated information about fungi and engineered bacteria in gastrointestinal infectious diseases, aiming for a more comprehensive overview of the role of the gut microbiome. This review will provide insights into the pathogenic mechanisms of the gut microbiome while exploring the microbiome's potential in the prevention, diagnosis, prediction, and treatment of gastrointestinal infections.

Anti-Biofilm Activity of Laurel Essential Oil against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a primary seafood-associated pathogen that could cause gastroenteritis. It can attach to various surfaces and form a biofilm, which poses serious threats to food safety. Hence, an effective strategy is urgently needed to control the biofilm formation of V. parahaemolyticus. Laurel essential oil (LEO) is used in food, pharmaceutical and other industries, and is commonly used as a flavoring agent and valuable spice in food industries. The potential antibiofilm effects of LEO against V. parahaemolyticus were examined in this study. LEO obviously reduced biofilm biomass at subinhibitory concentrations (SICs). It decreased the metabolic activity and viability of biofilm cells. Microscopic images and Raman spectrum indicted that LEO interfered with the structure and biochemical compositions of biofilms. Moreover, it also impaired swimming motility, decreased hydrophobicity, inhibited auto-aggregation and reduced attachment to different food-contact surfaces. RT-qPCR revealed that LEO significantly downregulated transcription levels of biofilm-associated genes of V. parahaemolyticus. These findings demonstrate that LEO could be potentially developed as an antibiofilm strategy to control V. parahaemolyticus biofilms in food industries.

Live and pasteurized Akkermansia muciniphila decrease susceptibility to Salmonella Typhimurium infection in mice

INTRODUCTION

The gut microbiome is vital for providing resistance against colonized pathogenicbacteria. Recently, specific commensal species have become recognized as important mediators of host defense against microbial infection by a variety of mechanisms.

OBJECTIVES

To examine the contribution of live and pasteurized A. muciniphila to defend against the intestinal pathogen Salmonella Typhimurium in a streptomycin-treated mouse model of infection.

METHODS

C57B6J mice were pretreated with phosphate-buffered saline (PBS), live Akkermansia muciniphila (AKK), and pasteurized A. muciniphila (pAKK) for two weeks, then mice were infected by S. Typhimurium SL 1344. 16S rRNA-based gut microbiota analysis was performed before and after infection. Bacterial counts in feces and tissues, histopathological analysis, gut barrier-related gene expression, and antimicrobial peptides were examined. Co-housing was performed to examine the role of microbiota in the change of susceptibility of mice to infection.

RESULTS

AKK and pAKK markedly decreased Salmonella fecal and systemic burdens and reduced inflammation during infection. Notably, further characterization of AKK and pAKK protective mechanisms revealed different candidate protective pathways. AKK promoted gutbarrier gene expression and the secretion of antimicrobial peptides, and co-housing studies suggested that AKK-associated microbial community played a role in attenuating infection. Moreover, pAKK had a positive effect on NLRP3 in infected mice. We verified that pretreatment of pAKK could promote the expression of NLRP3, and enhance the antimicrobial activity of macrophage, likely through increasing the production of reactive oxygen (ROS), nitric oxide (NO), and inflammatory cytokines.

CONCLUSION

Our study demonstrates that live or pasteurized A. muciniphila can be effective preventive measures for alleviating S. Typhimurium-induced disease, highlighting the potential of developing Akkermansia-based probiotics or postbiotics for the prevention of Salmonellosis.

Lactobacillus reuteri in digestive system diseases: focus on clinical trials and mechanisms

Objectives

Digestive system diseases have evolved into a growing global burden without sufficient therapeutic measures. Lactobacillus reuteri (L. reuteri) is considered as a new potential economical therapy for its probiotic effects in the gastrointestinal system. We have provided an overview of the researches supporting various L. reuteri strains' application in treating common digestive system diseases, including infantile colic, diarrhea, constipation, functional abdominal pain, Helicobacter pylori infection, inflammatory bowel disease, diverticulitis, colorectal cancer and liver diseases.

Methods

The summarized literature in this review was derived from databases including PubMed, Web of Science, and Google Scholar.

Results

The therapeutic effects of L. reuteri in digestive system diseases may depend on various direct and indirect mechanisms, including metabolite production as well as modulation of the intestinal microbiome, preservation of the gut barrier function, and regulation of the host immune system. These actions are largely strain-specific and depend on the activation or inhibition of various certain signal pathways. It is well evidenced that L. reuteri can be effective both as a prophylactic measure and as a preferred therapy for infantile colic, and it can also be recommended as an adjuvant strategy to diarrhea, constipation, Helicobacter pylori infection in therapeutic settings. While preclinical studies have shown the probiotic potential of L. reuteri in the management of functional abdominal pain, inflammatory bowel disease, diverticulitis, colorectal cancer and liver diseases, its application in these disease settings still needs further study.

Conclusion

This review focuses on the probiotic effects of L. reuteri on gut homeostasis via certain signaling pathways, and emphasizes the importance of these probiotics as a prospective treatment against several digestive system diseases.

A high-sucrose diet causes microbiota composition shift and promotes the susceptibility of mice to Salmonella Typhimurium infection

A westernized diet characterized by high fat and sugar is tightly associated with the development of metabolic diseases and inflammatory bowel disease. Although a high-fat diet has been extensively studied for its involvement in various diseases, fewer studies have examined the impact of a high-sugar diet on the development of certain diseases, particularly enteric infections. This study aimed to explore the effect of a high sucrose diet on Salmonella Typhimurium-induced infection. C57BL/6 mice received a normal diet (Control) or a high sucrose diet (HSD) for eight weeks and then were infected by Salmonella Typhimurium. The high-sugar diet profoundly altered the relative abundance of certain microbial taxa. Bacteroidetes and Verrucomicrobiota were more abundant in normal diet-fed mice than in HSD-fed mice. Moreover, short-chain fatty acids (SCFAs) and branched-chain fatty acids (BCFAs) were significantly higher in mice from the control group than the HSD group. More S. Typhimurium counts in feces and other tissues were observed in HSD-fed mice after infection. Tight junction proteins and antimicrobial peptides were significantly decreased in HSD-fed mice. Fecal microbiota transplantation (FMT) demonstrated that mice that received normal fecal microbiota had lower Salmonella Typhimurium burdens compared with mice that received HSD fecal microbiota, indicating that the altered microbial communities are associated with the severity of infection. Together, these findings suggest that the excessive intake of sucrose disturbs intestinal homeostasis and predisposes mice to Salmonella-induced infection.