Insights into the mechanisms and key factors influencing biofilm formation by Aeromonas hydrophila in the food industry: A comprehensive review and bibliometric analysis

Salinity-induced virulence alteration of Aeromonas hydrophila isolated from Scatophagus argus: insights from transcriptomic profiling and phenotypic characterization

BACKGROUND

The emerging foodborne pathogen, Aeromonas hydrophila, co-infects humans and animals, especially fish, threatening aquacultural production and public health. Previously, we found that Scatophagus argus, a widely cultivated fish species with high economic value, exhibited enhanced growth but increased susceptibility to A. hydrophila infection under freshwater conditions compared to seawater conditions. However, the exact mechanisms involved remain unclear.

RESULTS

Our study demonstrated that the enhanced virulence of A. hydrophila 201416, isolated from S. argus, in response to increasing salinity was associated with altered quorum sensing-related gene expression and regulated behaviors. Results from virulence assays incorporating phenotypic characterization indicated that elevated salinity levels (from 0 to 35‰) significantly hindered Ah201416 infection of S. argus. This trend correlated with increased biofilm mass and swimming motility, yet was inversely related to bacterial growth. RNA-sequencing and quantitative reverse transcriptional PCR analysis confirmed significant upregulation of genes related to flagellar assembly (flgB, flgH, flgC, flgI, flhA, and fliA), bacterial secretion (HlyD and Ahh1), and quorum sensing (AhyR, LuxO, and LuxE) of Ah201416 in response to elevated salinity. These findings suggested that increased salinity not only enhanced the virulence of Ah201416 but also bolstered the resistance of S. argus, thereby mitigating its susceptibility.

CONCLUSIONS

This study provides deeper insights into the microbial risks associated with A. hydrophila in aquacultural production, which is critical to developing effective prevention and control strategies and ensuring a safe seafood supply.

CLINICAL TRIAL NUMBER

Not applicable.

Microbiota Dysbiosis in Mytilus chilensis Is Induced by Hypoxia, Leading to Molecular and Functional Consequences

Bivalve microbiota play a vital role in host health, supporting nutrient processing, immunity, and disease resistance. However, the increasing hypoxia in Chilean coastal waters, caused by climate change and eutrophication, threatens to disrupt this microbial balance, potentially promoting pathogens and impairing essential functions. Mytilus chilensis is vulnerable to hypoxia-reoxygenation cycles, yet the effects on its microbiota remain poorly understood. This study investigates the impact of hypoxia on the structure and functional potential of the microbial communities residing in the gills and digestive glands of M. chilensis. Employing full-length 16S rRNA gene sequencing, we explored hypoxia's effects on microbial diversity and functional capacity. Our results revealed significant alterations in the microbial composition, with a shift towards facultative anaerobes thriving in low oxygen environments. Notably, there was a decrease in dominant bacterial taxa such as Rhodobacterales, while opportunistic pathogens such as Vibrio and Aeromonas exhibited increased abundance. Functional analysis indicated a decline in critical microbial functions associated with nutrient metabolism and immune support, potentially jeopardizing the health and survival of the host. This study sheds light on the intricate interactions between host-associated microbiota and environmental stressors, underlining the importance of managing the microbiota in the face of climate change and aquaculture practices.

Ultrasound and lactic/malic acid treatment for mitten crab decontamination: Efficacy and mechanisms against A. hydrophila

The Chinese mitten crab (Eriocheir sinensis), recognized as a high-value aquatic product, necessitates effective cleaning to ensure both safety and quality. Conventional cleaning methods frequently fail to eliminate biofilms and pathogenic bacteria, such as Aeromonas hydrophila, which pose significant health risks and contribute to spoilage. This study explores the bactericidal efficacy and underlying mechanisms of ultrasound treatment combined with a lactic acid and malic acid complex solution for decontaminating crabs and enhancing food safety. Employing a range of methodologies, including microscopic imaging, live/dead staining, RT-qPCR, and texture and microstructure analysis, the results indicate that the combined treatment significantly reduced A. hydrophila counts by 4.16 lg CFU/mL and induced substantial bacterial membrane damage, as evidenced by scanning electron microscopy (SEM). Gene expression analysis revealed a pronounced downregulation of biofilm-related genes. Notably, the treatment also preserved the texture and sensory properties of crab meat, thereby ensuring high product quality. These findings suggest that the application of ultrasound in conjunction with a lactic acid-malic acid solution represents a green and effective strategy for improving food safety and quality in the processing of aquatic products, offering a sustainable and eco-friendly alternative to traditional cleaning methods.

Targeted insights into Aeromonas hydrophila biofilms: Surface preferences, resistance mechanisms, and gene expression

This study provides a comprehensive analysis of biofilm formation, antibiotic resistance, motility, and gene expression in four Aeromonas hydrophila strains-ATCC 15467, ATCC 7966, KCTC 2358, and KCTC 11533-on stainless steel (SS), silicon rubber (SR), polyethylene terephthalate (PET), and high-density polyethylene (HDPE) surfaces over 24, 48, 72, and 96 h. Biofilm formation peaked at 72 h, with ATCC 7966 demonstrating the highest biofilm density on PET (6.50 ± 0.08 log CFU/cm²), underscoring PET's role as a favorable substrate for biofilm development. In contrast, HDPE consistently exhibited the lowest biofilm levels, reflecting its potential as a biofilm-resistant material. Antibiotic susceptibility profiling revealed multidrug resistance (MDR) in ATCC 15467 and KCTC 11533 (MARI = 0.80), particularly against beta-lactams, aminoglycosides, and fluoroquinolones while ATCC 7966 and KCTC 2358 displayed moderate resistance. Motility assays highlighted strain-specific capabilities, with KCTC 11533 exhibiting the highest swimming motility (76.0 ± 6.6 mm) and KCTC 2358 excelling in swarming (47.7 ± 3.5 mm). Genetic analysis confirmed the presence of luxS and ahyR in all strains, while csgA was exclusive to ATCC 7966, correlating with its superior biofilm formation. Confocal microscopy revealed biofilm maturation dynamics, with red fluorescence indicating cell death and aging at 96 h, while SEM images captured intricate surface-specific biofilm architectures. These findings elucidate the critical interplay between strain characteristics, surface properties, and incubation time, providing a foundation for developing targeted strategies to control A. hydrophila biofilms in food processing environments.

Exposure to low concentrations of ethanol alters global gene expression patterns in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a foodborne pathogen commonly associated with seafood worldwide. Ethanol is widely used as a disinfectant and preservative in the food industry. Low concentrations of ethanol can inhibit the growth of V. parahaemolyticus and alter its protein expression profile and stress resistance. However, it remains unknown how ethanol exposure affects the behavior and gene expression of V. parahaemolyticus. In this study, RNA sequencing revealed differential expression of 1020 genes in response to 1.5 % (v/v) ethanol, including biofilm-associated genes, c-di-GMP metabolism-related genes, major virulence genes, putative regulatory genes, and Hsp-like protein encoding genes. Specifically, genes involved in exopolysaccharides, type VI secretion system 1, thermostable direct hemolysin, and type III secretion system 2 were upregulated upon exposure to 1.5 % ethanol. Additionally, the data also suggest a significant decrease in swimming and swarming motility, as well as a notable increase in biofilm formation, under 1.5 % ethanol stress. This study enhances our understanding of how V. parahaemolyticus adapts its behavior and gene expression to low concentrations of ethanol.

Mechanistic and bibliometric insights into RpoS-mediated biofilm regulation and its strategic role in food safety applications

Biofilm, complex structures formed by microorganisms within an extracellular polymeric matrix, pose significant challenges in the sector by harboring dangerous pathogens and complicating decontamination, thereby increasing the risk of foodborne illnesses. This article provides a comprehensive review of the sigma factor, rpoS's role in biofilm development, specifically in gram-negative bacteria, and how the genetic, environmental, and regulatory elements influence rpoS activity with its critical role in bacterial stress responses. Our findings reveal that rpoS is a pivotal regulator of biofilm formation, enhancing bacterial survival in adverse conditions. Key factors affecting rpoS activity include oxidative and osmotic stress and nutrient availability. Understanding rpoS-mediated regulatory pathways is essential for developing targeted biofilm management strategies to improve food quality and safety. Furthermore, a bibliometric analysis highlights significant research trends and gaps in the literature, guiding future research directions. Future research should focus on detailed mechanistic studies of rpoS-mediated biofilm regulation, the development of specific rpoS inhibitors, and innovative approaches like biofilm-resistant surface coatings. This knowledge can lead to more effective contamination prevention and overall food safety enhancements.

Bibliometric Analysis of Probiotic Bacillus in Food Science: Evolution of Research Trends and Systematic Evaluation

With the in-depth and comprehensive research on probiotic Bacillus, it has become a hot topic in food science. However, the current status of research using bibliometric analysis to assess the application of probiotic Bacillus in food science has not been comprehensively reviewed. The Web of Science (WOS) database was used in this review's bibliometric analysis to determine the hotspots for research as well as the extent of completed experiments. Furthermore, a systematic review was conducted on the research hotspots of probiotic Bacillus in food science. The comprehensive analysis showed it was a growing and global research field. The keywords with high frequency mainly included "spore," "strain," and "production," which were research hot topics in the last decade. The application of the spore form or nutrient cells of probiotic Bacillus in industrialized food production through nutrient fortification, fermentation agents, and highly efficient synthesis of metabolites showed great development potential.

Novel insights into biofilm formation and the key differentially expressed genes in Yersinia enterocolitica from meat: Implications for food safety and disease prevention

Yersinia enterocolitica is an important foodborne pathogen that can cause a zoonotic disease known as yersiniosis, which causes symptoms such as acute diarrhea, mesenteric adenitis, terminal ileum inflammation, pseudo appendicitis, sepsis, and other complications. The mechanism of biofilm formation in Y. enterocolitica remains poorly understood, with limited research available on this topic. This study systematically examined the distribution characteristics and biofilm formation ability of Y. enterocolitica isolated from poultry and livestock related samples. Analysis of food samples collected indicated significant presence of Y. enterocolitica (207/670, 30.9 %), particularly in frozen duck meat (7/11, 63.6 %). Majority of the isolated strains did not demonstrate biofilm-forming ability (52.7 %), while a notable percentage exhibited moderate (6.8 %) to strong (11.6 %) biofilm-forming ability. Additionally, a significant percentage of strains (16/207, 7.7 %) displayed extremely high optical density/cut-off OD (OD/ODC) ratios (the average OD value of each sample divided by the average OD value of the negative controls of each 96-well plate plus 3 standard deviations) (exceeding 10). Time-course analysis of biofilm formation in 10 isolates revealed three distinct patterns: (i) rapid increase from 6 h to 12 h, with gradual peak between 48 and 72 h followed by a slight decline and stabilization; (ii) little biofilm formation at 24 h with a gradual increase up to 96 h, maintaining this level until 120 h; and (iii) complete absence of biofilm formation throughout the experiment. Subsequent examination of differentially expressed genes (DEGs) in planktonic cells and biofilms of two strains with distinct biofilm formation capabilities identified seven metabolic pathways, including ribosome, photosynthesis, fatty acid degradation, valine, leucine, and isoleucine degradation, as well as pinene, camphor, and geraniol degradation. Significantly elevated expression levels of genes associated with flagellar assembly, bacterial chemotaxis, and quorum sensing (partially) were observed exclusively in planktonic cells of the selected strain with stronger biofilm-forming ability, implying that the heightened expression of flagellar assembly and bacterial chemotaxis-related genes is an important but not sole determinant of biofilm formation. The study contributes to the elucidation of the underlying mechanisms governing biofilm formation in Y. enterocolitica and may offer valuable insights for the advancement of novel food safety strategies.

Bacterial Adhesion to Natural and Synthetic Fibre-Forming Polymers: Influence of Material Properties

Polymer-based textiles have a major impact on human well-being, as they provide the desired functional protection and aesthetic comfort when worn. However, natural and synthetic polymer-based textiles can also pose serious health risks, as they are surfaces that allow the adhesion of various bacteria, including pathogenic bacteria. To minimise these problems, antibacterial chemical treatments are generally applicable in the case of polymer-based textiles. However, to avoid the use of potentially toxic chemicals, sustainable approaches require the customised design of non-adhesive polymer-based textiles, considering their chemical, physicochemical, constructional, and textural properties. Before designing, several articles are required to gain sufficient knowledge of the described object. Despite the urgent need to combat bacteria (on polymer-based textiles), which pose a serious global health risk, only a few review articles have been published that address bacterial adhesion in the context of superhydrophobic and antibacterial textile materials, while only one review article holistically addresses the textile factors and their influence on this phenomenon. The aim of this review article is to expand the insufficient knowledge about bacterial adhesion to polymer-based textiles on the basis of theoretical findings and real examples through a high degree of structuring, simplification, holistic consideration, and visualization. Therefore, this review provides an insight into the mechanisms involved in bacterial adhesion and a comprehensive overview of the influence of different textile factors, such as chemical composition, hydrophilicity/hydrophobicity, surface charge, surface free energy, roughness, and porosity, on bacterial adhesion. To emphasise the importance of the synergistic effect of the combined textile factors, examples of the influence of hydrophilicity/hydrophobicity in combination with surface charge, surface roughness, and porosity are discussed. From the review, it can be concluded that the combination of hydrophilicity/hydrophobicity and the surface charge of textile fibres and bacteria is crucial for bacterial adhesion, with roughness and porosity being the most important factors among the constructive and textural properties of polymer-based textiles.

Assessment of Vibrionaceae prevalence in seafood from Qidong market and analysis of Vibrio parahaemolyticus strains

The aim of this study was to investigate the prevalence of Vibrionaceae family in retail seafood products available in the Qidong market during the summer of 2023 and to characterize Vibrio parahaemolyticus isolates, given that this bacterium is the leading cause of seafood-associated food poisoning. We successfully isolated a total of 240 Vibrionaceae strains from a pool of 718 seafood samples. The breakdown of the isolates included 146 Photobacterium damselae, 59 V. parahaemolyticus, 18 V. campbellii, and 11 V. alginolyticus. Among these, P. damselae and V. parahaemolyticus were the predominant species, with respective prevalence rates of 20.3% and 8.2%. Interestingly, all 59 isolates of V. parahaemolyticus were identified as non-pathogenic. They demonstrated proficiency in swimming and swarming motility and were capable of forming biofilms across a range of temperatures. In terms of antibiotic resistance, the V. parahaemolyticus isolates showed high resistance to ampicillin, intermediate resistance to cefuroxime and cefazolin, and were sensitive to the other antibiotics evaluated. The findings of this study may offer valuable insights and theoretical support for enhancing seafood safety measures in Qidong City.

Quercetin disrupts biofilm formation and attenuates virulence of Aeromonas hydrophila

Aeromonas hydrophila poses significant health and economic challenges in aquaculture owing to its pathogenicity and prevalence. Overuse of antibiotics has led to multidrug resistance and environmental pollution, necessitating alternative strategies. This study investigated the antibacterial and antibiofilm potentials of quercetin against A. hydrophila. Efficacy was assessed using various assays, including antibacterial activity, biofilm inhibition, specific growth time, hemolysis inhibition, autoaggregation, and microscopic evaluation. Additionally, docking analysis was performed to explore potential interactions between quercetin and virulence proteins of A. hydrophila, including proaerolysin, chaperone needle-subunit complex of the type III secretion system, and alpha-pore forming toxin (PDB ID: 1PRE, 2Q1K, 6GRK). Quercetin exhibited potent antibacterial activity with 21.1 ± 1.1 mm zone of inhibition at 1.5 mg mL-1. It also demonstrated significant antibiofilm activity, reducing biofilm formation by 46.3 ± 1.3% at the MIC and attenuating autoaggregation by 55.9 ± 1.5%. Hemolysis was inhibited by 41 ± 1.8%. Microscopic analysis revealed the disintegration of the A. hydrophila biofilm matrix. Docking studies indicated active hydrogen bond interactions between quercetin and the targeted virulence proteins with the binding energy -3.2, -5.6, and -5.1 kcal mol⁻1, respectively. These results suggest that quercetin is an excellent alternative to antibiotics for combating A. hydrophila infection in aquaculture. The multifaceted efficacy of quercetin in inhibiting bacterial growth, biofilm formation, virulence factors, and autoaggregation highlights the potential for aquaculture health and sustainability. Future research should delve into the precise mechanisms of action and explore synergistic combinations with other compounds for enhanced efficacy and targeted interventions.

Biofilm formation: mechanistic insights and therapeutic targets

Biofilms are complex multicellular communities formed by bacteria, and their extracellular polymeric substances are observed as surface-attached or non-surface-attached aggregates. Many types of bacterial species found in living hosts or environments can form biofilms. These include pathogenic bacteria such as Pseudomonas, which can act as persistent infectious hosts and are responsible for a wide range of chronic diseases as well as the emergence of antibiotic resistance, thereby making them difficult to eliminate. Pseudomonas aeruginosa has emerged as a model organism for studying biofilm formation. In addition, other Pseudomonas utilize biofilm formation in plant colonization and environmental persistence. Biofilms are effective in aiding bacterial colonization, enhancing bacterial resistance to antimicrobial substances and host immune responses, and facilitating cell‒cell signalling exchanges between community bacteria. The lack of antibiotics targeting biofilms in the drug discovery process indicates the need to design new biofilm inhibitors as antimicrobial drugs using various strategies and targeting different stages of biofilm formation. Growing strategies that have been developed to combat biofilm formation include targeting bacterial enzymes, as well as those involved in the quorum sensing and adhesion pathways. In this review, with Pseudomonas as the primary subject of study, we review and discuss the mechanisms of bacterial biofilm formation and current therapeutic approaches, emphasizing the clinical issues associated with biofilm infections and focusing on current and emerging antibiotic biofilm strategies.