Food color 'Azorubine' interferes with quorum sensing regulated functions and obliterates biofilm formed by food associated bacteria: An in vitro and in silico approach

Targeting motility of Listeria monocytogenes: Alternative strategies to control foodborne illness

Listeria monocytogenes, a gram-positive facultative anaerobic bacterium, demonstrates remarkable adaptability to various environmental stressors in food processing environments. It can survive and grow under extremely challenging environmental conditions such as low pH and temperatures, high salinity, and UV radiation. Its ability to generate biofilms at multiple stages of the food processing chain poses significant food safety issues. This bacterium is known for causing severe listeriosis, making it a major problem in microbiology and food safety. L. monocytogenes relies on motility to explore surfaces, attach, and build biofilms. It comprises actin-based motility, which is used for cell-to-cell propagation inside host tissues, and flagellar-driven motility, which assists in surface colonization and infection spread. Flagellar motility also plays an important function in increasing virulence throughout infection cycles. L. monocytogenes motility is regulated by a complex network of regulatory proteins that govern the expression of motility-associated genes. These proteins directly impact pathogenicity by influencing motility and biofilm formation, as well as an indirect impact via regulatory pathways. Efforts to control L. monocytogenes infections and decrease food safety impact include a variety of procedures. Natural compounds, synthetic agents, nanomaterials, and conjugates have emerged as intriguing options for inhibiting motility, disrupting biofilm formation, and reducing virulence. These strategies focus on vital elements of the L. monocytogenes life cycle and pathophysiology to improve food safety and public health. This review provides a comprehensive discussion of the regulatory mechanisms governing L. monocytogenes motility, emphasizing their role in pathogenicity, and explores potential strategies for attenuating the motility and virulence properties. Understanding these mechanisms is essential for developing targeted therapeutic approaches against L. monocytogenes infections and improving food safety practices.

In-silico and in-vitro assessment of the antibiofilm potential of azo dye, carmoisine against Pseudomonas aeruginosa

Biofilm is a community of microorganisms attached to the substrate and plays a significant role in microbial pathogenesis and medical device-related infection. Pseudomonas aeruginosa (PA) is a highly infectious gram-negative opportunistic biofilm-forming bacterium with high antibiotic resistance. Several reports underscore the antimicrobial activity of natural and synthetic food coloring agents, including carmoisine, turmeric dye, red amaranth dye, and phloxine B. However, their ability to suppress the PA biofilm is not clearly understood. Carmoisine is a red-colored synthetic azo dye containing naphthalene subunits and sulfonic groups and is widely used as a food coloring agent. This study investigated the antibiofilm potential and possible mechanism of biofilm inhibition by carmoisine against PA. Computational studies through molecular docking revealed that carmoisine strongly binds to QS regulator LasR (-12.7) and relatively less strongly but significantly with WspR (-6.9). Further analysis of the docked LasR-carmoisine complex using 100 ns MD simulation (Desmond, Schrödinger) validated the bonding strength and stability. Crystal violet assay, triphenyl tetrazolium chloride salt assay, and confocal microscopic studies were adopted for biofilm quantification, and the results indicated the dose-dependent antibiofilm activity of carmoisine against PA. We hypothesise that the carmoisine-mediated reduction of biofilm in PA is due to its interaction with LasR and interference with the QS system. The computational and biochemical analysis of another compound, 1,2-naphthoquinone-4-sulphonic acid, reiterated the role of the naphthalene ring in biofilm inhibition. Hence, this work will pave the way for the future discovery of antibiofilm drugs based on naphthalene ring-based lead compounds.Communicated by Ramaswamy H. Sarma.

Exploring the Function of Quorum Sensing Regulated Biofilms in Biological Wastewater Treatment: A Review

Quorum sensing (QS), a type of bacterial cell–cell communication, produces autoinducers which help in biofilm formation in response to cell population density. In this review, biofilm formation, the role of QS in biofilm formation and development with reference to biological wastewater treatment are discussed. Autoinducers, for example, acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2, present in both Gram-negative and Gram-positive bacteria, with their mechanism, are also explained. Over the years, wastewater treatment (WWT) by QS-regulated biofilms and their optimization for WWT have gained much attention. This article gives a comprehensive review of QS regulation methods, QS enrichment methods and QS inhibition methods in biological waste treatment systems. Typical QS enrichment methods comprise adding QS molecules, adding QS accelerants and cultivating QS bacteria, while typical QS inhibition methods consist of additions of quorum quenching (QQ) bacteria, QS-degrading enzymes, QS-degrading oxidants, and QS inhibitors. Potential applications of QS regulated biofilms for WWT have also been summarized. At last, the knowledge gaps present in current researches are analyzed, and future study requirements are proposed.

The protective effect of natural phenolic compound on the functional and structural responses of inhibited catalase by a common azo food dye

In this research retrieval effects of natural yellow (NY) on the performance of carmoisine (CAR) inhibited bovine liver catalase (BLC) was studied using multispectral and theoretical methods. Kinetic studies showed that CAR inhibited BLC through competitive inhibition (IC₅₀ value of 2.24 × 10^-6 M) while the addition of NY recover the activity of CAR-BLC up to 82% in comparison with the control enzyme. Circular dichroism data revealed that NY can repair the structural changes of BLC, affected by CAR. Furthermore, an equilibrium dialysis study indicated that NY could reduce the stability of the CAR-catalase complex. The surface plasmon resonance (SPR) data analysis indicated a high affinity of NY to BLC compared to CAR and the binding of NY led to a decrease in the affinity of the enzyme to the inhibitor. On the other hand, fluorescence and molecular docking studies showed that the quenching mechanism of BLC by CAR occurs through a static quenching process, and van der Waals forces and hydrogen bonding play a crucial role in the binding of CAR to BLC. MLSD data demonstrated that NY could increase the binding energy of CAR-BLC complex from -7.72 kJ mol^-1 to -5.9 kJ mol^-1, leading to complex instability and catalase activity salvage.

Promising strategies to control persistent enemies: Some new technologies to combat biofilm in the food industry-A review

Biofilm is an advanced form of protection that allows bacterial cells to withstand adverse environmental conditions. The complex structure of biofilm results from genetic-related mechanisms besides other factors such as bacterial morphology or substratum properties. Inhibition of biofilm formation of harmful bacteria (spoilage and pathogenic bacteria) is a critical task in the food industry because of the enhanced resistance of biofilm bacteria to stress, such as cleaning and disinfection methods traditionally used in food processing plants, and the increased food safety risks threatening consumer health caused by recurrent contamination and rapid deterioration of food by biofilm cells. Therefore, it is urgent to find methods and strategies for effectively combating bacterial biofilm formation and eradicating mature biofilms. Innovative and promising approaches to control bacteria and their biofilms are emerging. These new approaches range from methods based on natural ingredients to the use of nanoparticles. This literature review aims to describe the efficacy of these strategies and provide an overview of recent promising biofilm control technologies in the food processing sector.

Naringin inhibits the biofilms of metallo-β-lactamases (MβLs) producing Pseudomonas species isolated from camel meat

Food producing animals harbouring bacteria carrying drug resistance genes especially the metallo-beta-lactamase (MBL) pose high risk for the human population. In addition, formation of biofilm by these drug resistant pathogens represents major threat to food safety and public health. In this study, metallo-β-lactamases (MβLs) producing Pseudomonas spp. from camel meat were isolated and assessed for their biofilm formation. Further, in vitro and in silico studies were performed to study the effect of flavone naringin on biofilm formation against isolated Pseudomonas spp. A total of 55% isolates were found to produce metallo-β-lactamase enzyme. Naringin mitigated biofilm formation of Pseudomonas isolates up to 57%. Disturbed biofilm architecture and reduced the colonization of bacteria on glass was observed under scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). The biofilm related traits such as exopolysaccharides (EPS) and alginate production was also reduced remarkably in the presence of naringin. Eradication of preformed biofilms (32–60%) was also observed at the respective 0.50 × MICs. Molecular docking revealed that naringin showed strong affinity towards docked proteins with binding energy ranging from −8.6 to −8.8 kcal mol⁻¹. Presence of metallo-β-lactamase producers indicates that camel meat could be possible reservoir of drug-resistant Pseudomonas species of clinical importance. Naringin was successful in inhibiting biofilm formation as well as eradicating the preformed biofilms and demonstrated strong binding affinity towards biofilm associated protein. Thus, it is envisaged that naringin could be exploited as food preservative especially against the biofilm forming food-borne Pseudomonas species and is a promising prospect for the treatment of biofilm based infections.

Fabrication of Zinc Oxide-Xanthan Gum Nanocomposite via Green Route: Attenuation of Quorum Sensing Regulated Virulence Functions and Mitigation of Biofilm in Gram-Negative Bacterial Pathogens

The unabated abuse of antibiotics has created a selection pressure that has resulted in the development of antimicrobial resistance (AMR) among pathogenic bacteria. AMR has become a global health concern in recent times and is responsible for a high number of mortalities occurring across the globe. Owing to the slow development of antibiotics, new chemotherapeutic antimicrobials with a novel mode of action is required urgently. Therefore, in the current investigation, we green synthesized a nanocomposite comprising zinc oxide nanoparticles functionalized with extracellular polysaccharide xanthan gum (ZnO@XG). Synthesized nanomaterial was characterized by structurally and morphologically using UV-visible spectroscopy, XRD, FTIR, BET, SEM and TEM. Subinhibitory concentrations of ZnO@XG were used to determine quorum sensing inhibitory activity against Gram-negative pathogens, Chromobacterium violaceum, and Serratia marcescens. ZnO@XG reduced quorum sensing (QS) regulated virulence factors such as violacein (61%), chitinase (70%) in C. violaceum and prodigiosin (71%) and protease (72%) in S. marcescens at 128 µg/mL concentration. Significant (p ≤ 0.05) inhibition of biofilm formation as well as preformed mature biofilms was also recorded along with the impaired production of EPS, swarming motility and cell surface hydrophobicity in both the test pathogens. The findings of this study clearly highlight the potency of ZnO@XG against the QS controlled virulence factors of drug-resistant pathogens that may be developed as effective inhibitors of QS and biofilms to mitigate the threat of multidrug resistance (MDR). ZnO@XG may be used alone or in combination with antimicrobial drugs against MDR bacterial pathogens. Further, it can be utilized in the food industry to counter the menace of contamination and spoilage caused by the formation of biofilms.

Bio-inspired facile fabrication of silver nanoparticles from in vitro grown shoots of Tamarix nilotica: explication of its potential in impeding growth and biofilms of Listeria monocytogenes and assessment of wound healing ability

Novel, safe, and effective antilisterial agents are required in order to prevent Listeria monocytogenes infections and maintain food safety. This study synthesized silver nanoparticles (AgNPs) from the shoot extract of in vitro-grown Tamarix nilotica (TN) and characterized them using X-ray diffraction, Fourier transform infrared spectroscopy, UV-visible spectroscopy, dynamic light scattering, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS), and transmission electron microscopy (TEM). We also assessed the antilisterial potential of the synthesized TN-AgNPs by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against two strains of L. monocytogenes and L. innocua. TN-AgNPs (2×MICs) showed a significant decrease in growth in all Listeria test strains. Release of cellular content and cell morphology analysis of TN-AgNP-treated bacterial cells demonstrated the mechanism of bactericidal activity of AgNPs. In addition, TN-AgNPs induced a significant decrease in swimming motility (62-71%), biofilm formation (57-64%), and preformed biofilms (48-58%) in all Listeria test strains at sub-inhibitory concentrations. Microtitre plate assay results for biofilm inhibition were confirmed by SEM and CLSM visualization of TN-AgNP-treated and TN-AgNP-untreated Listeria test strains. TN-AgNPs also showed wound-healing activity in MCF-7 cells by inhibiting cell migration in a scratch plate assay. TN-AgNP-induced enhanced reactive oxygen species generation in treated cells could be a plausible reason for the biofilm inhibitory activity of AgNPs. TN-AgNPs having antilisterial, antibiofilm, and wound-healing properties can be effectively used to prevent L. monocytogenes infections in the food industry and healthcare.