Combined effects of Allium sativum and Cuminum cyminum essential oils on planktonic and biofilm forms of Salmonella typhimurium isolates

Application of bacterioruberin from Arthrobacter sp. isolated from Xinjiang desert to extend the shelf-life of fruits during postharvest storage

Post-harvest losses and rapid fruit ripening at room temperature are major challenges in preserving fruit quality. This study aimed to reduce such losses by applying a red carotenoid pigment, bacterioruberin extracted from an Arthrobacter sp. The carotenoid was characterized as bacterioruberin and its derivative tetra anhydrous bacterioruberin (λmax 490 nm), and an m/z value of 675 and 742 (M+ 1H)+1. The annotated LIPID MAP demonstrated the presence of over 360 isoprenoids annotated transcripts. The compound exhibited significant antioxidant activity, with an IC50 of 22 μg/mL, iron chelation and antibacterial activities indicating its potential as a natural preservative. When applied to grapes, peaches, and apricots, bacterioruberin (2 %) effectively prevented spoilage for six days at room temperature. Statistical analysis using one-way ANOVA revealed a significant correlation (p = 0.05) between treated and control groups in subjective quality attributes. Computational investigation with phospholipase D and VQ22 motif protein further supported the preservative potential of bacterioruberin.

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.

Anti-biofilm mechanisms of action of essential oils by targeting genes involved in quorum sensing, motility, adhesion, and virulence: A review

Biofilms are a critical factor for food safety, causing important economic losses. Among the novel strategies for controlling biofilms, essential oils (EOs) can represent an environmentally friendly approach, able to act both on early and mature stages of biofilm formation. This review reports the anti-biofilm mechanisms of action of EOs against five pathogenic bacterial species known for their biofilm-forming ability. These mechanisms include disturbing the expression of genes related to quorum sensing (QS), motility, adhesion, and virulence. Biofilms and QS are interconnected processes, and EOs interfere with the communication system (e.g. regulating the expression of agrBDCA, luxR, luxS, and pqsA genes), thus influencing biofilm formation. In addition, QS is an important mechanism that regulates gene expression related to bacterial survival, virulence, and pathogenicity. Similarly, EOs also influence the expression of many virulence genes. Moreover, EOs exert their effects modulating the genes associated with bacterial adhesion and motility, for example those involved in curli (csg), fimbriae (fim, lpf), and flagella (fla, fli, flh, and mot) production, as well as the ica genes responsible for synthetizing polysaccharide intercellular adhesin. This review provides a comprehensive framework on the topic for a better understanding of EOs biofilm mechanisms of action.

Biofilm formation in food processing plants and novel control strategies to combat resistant biofilms: the case of Salmonella spp

Salmonella is one of the pathogens that cause many foodborne outbreaks throughout the world, representing an important global public health problem. Salmonella strains with biofilm-forming abilities have been frequently isolated from different food processing plants, especially in poultry industry. Biofilm formation of Salmonella on various surfaces can increase their viability, contributing to their persistence in food processing environments and cross-contamination of food products. In recent years, increasing concerns arise about the antimicrobial resistant and disinfectant tolerant Salmonella, while adaptation of Salmonella in biofilms to disinfectants exacerbate this problem. Facing difficulties to inhibit or remove Salmonella biofilms in food industry, eco-friendly and effective strategies based on chemical, biotechnological and physical methods are in urgent need. This review discusses biofilm formation of Salmonella in food industries, with emphasis on the current available knowledge related to antimicrobial resistance, together with an overview of promising antibiofilm strategies for controlling Salmonella in food production environments.

Carvacrol inhibits bacterial polysaccharide intracellular adhesin synthesis and biofilm formation of mucoid Staphylococcus aureus: an in vitro and in vivo study

Staphylococcus aureus (S. aureus) is one of the important human pathogens and causes both superficial and systemic infections. More importantly, the formation of S. aureus biofilms, a main cause of its pathogenicity and drug resistance, has been a critical challenge in clinical treatment. Carvacrol, a plant-based natural product, has gained great interest for therapeutic purposes due to its effective biological activity with low cytotoxicity. The present study aimed to investigate the effect of carvacrol on anti-biofilm activity. Growth curve analysis showed that applying a sub-inhibitory concentration of carvacrol (4 μg mL-1) was not lethal to S. aureus SYN; however, the inhibition rate of biofilm formation was as high as 63.6%, and the clearance rate of mature biofilms was as high as 30.7%. In addition, carvacrol effectively reduced the production of biofilm-associated extracellular polysaccharides and showed no effect on eDNA release. Furthermore, qPCR analysis revealed that carvacrol significantly down-regulated the expression of icaA, icaB, icaC, agrA, and sarA (P < 0.05). The in vivo efficacy of carvacrol against biofilm infection was further verified with a biological model of G. mellonella larvae. The results showed that carvacrol was non-toxic to the larvae and can effectively increase the survival rate of the larvae infected with S. aureus strain SYN.

Photodynamic Therapy and Its Synergism with Melittin Against Drug-Resistant Acinetobacter baumannii Isolates with High Biofilm Formation Ability

Drug-resistant biofilm producer A. baumannii isolates are a global concern that warns researchers about the development of new treatments. This study was designed to analyze the effect of photodynamic therapy (PDT) as monotherapy and associated with melittin on multidrug-resistant A. baumannii isolates. Sub-lethal doses of photosensitizer, LED, and PDT were determined. The PDT effect on the biofilm and expression of biofilm-associated genes was evaluated by scanning electron microscopy and quantitative real-time PCR (qRT-PCR) methods, respectively. The synergistic effect of PDT and melittin on the survival of MDR/XDR strong biofilm producer isolates was evaluated by checkerboard assay. Survival rates were significantly decreased at the lowest concentration of 12.5-50 μg/ml in 4 min at an energy density of 93.75 J/cm2 (P < 0.05). The optimized PDT method had a bactericidal effect against all tested groups, and the mean expression levels of csu, abaI, bap, and ompA genes in the strong biofilm producers were decreased significantly compared to the control group. The combined effect of LED and melittin successfully reduced the MDR/XDR A. baumannii strong biofilm producers' growth from 3.1 logs. MB-mediated aPDT and combined treatment of PDT with melittin, which has been investigated for the first time in this study, can be an efficient strategy against MDR/XDR A. baumannii isolates with strong biofilm production capacity.

Antibiofilm Action of Plant Terpenes in Salmonella Strains: Potential Inhibitors of the Synthesis of Extracellular Polymeric Substances

Salmonella can form biofilms that contribute to its resistance in food processing environments. Biofilms are a dense population of cells that adhere to the surface, creating a matrix composed of extracellular polymeric substances (EPS) consisting mainly of polysaccharides, proteins, and eDNA. Remarkably, the secreted substances, including cellulose, curli, and colanic acid, act as protective barriers for Salmonella and contribute to its resistance and persistence when exposed to disinfectants. Conventional treatments are mostly ineffective in controlling this problem; therefore, exploring anti-biofilm molecules that minimize and eradicate Salmonella biofilms is required. The evidence indicated that terpenes effectively reduce biofilms and affect their three-dimensional structure due to the decrease in the content of EPS. Specifically, in the case of Salmonella, cellulose is an essential component in their biofilms, and its control could be through the inhibition of glycosyltransferase, the enzyme that synthesizes this polymer. The inhibition of polymeric substances secreted by Salmonella during biofilm development could be considered a target to reduce its resistance to disinfectants, and terpenes can be regarded as inhibitors of this process. However, more studies are needed to evaluate the effectiveness of these compounds against Salmonella enzymes that produce extracellular polymeric substances.

Activity of Antibiotics and Potential Antibiofilm Agents against Biofilm-Producing Mycobacterium avium-intracellulare Complex Causing Chronic Pulmonary Infections

Nontuberculous mycobacteria (NTM) cause lung infections in patients with underlying pulmonary diseases (PD). The Mycobacteriumavium-intracellulare complex (MAC) is the most frequently involved NTM. The MAC-PD treatment is based on the administration of several antibiotics for long periods of time. Nonetheless, treatment outcomes remain very poor. Among the factors involved is the ability of MAC isolates to form biofilm. The aim of the study was to assess the in vitro activity of different antibiotics and potential antibiofilm agents (PAAs) against MAC biofilm. Four antibiotics and six PAAs, alone and/or in combination, were tested against planktonic forms of 11 MAC clinical isolates. Biofilm was produced after 4 weeks of incubation and analyzed with the crystal violet assay. The antibiotics and PAAs were tested by measuring the absorbance (minimum biofilm inhibition concentrations, MBICs) and by performing subcultures (minimum biofilm eradication concentrations, MBECs). The clarithromycin/amikacin and clarithromycin/ethambutol combinations were synergistic, decreasing the MBECs values compared to the individual antibiotics. The amikacin/moxifloxacin combination showed indifference. The MBIC values decreased significantly when PAAs were added to the antibiotic combinations. These results suggest that antibiotic combinations should be further studied to establish their antibiofilm activity. Moreover, PAAs could act against the biofilm matrix, facilitating the activity of antibiotics.

Anti-Biofilms’ Activity of Garlic and Thyme Essential Oils against Salmonella typhimurium

Biofilm control by essential oil (EO) application has recently increased to preclude biofilm production on foods and environmental surfaces. In this work, the anti-biofilm effects of garlic and thyme essential oils using the minimum inhibitory concentration (MIC) method against Salmonella typhimurium recovered from different abattoir samples were investigated along with the virulence genes (InvA, SdiA and Stn genes), and the antimicrobial susceptibility profile of S. typhimurium as well. The obtained results revealed that S. typhimurium contaminated abattoir samples to varying degrees. The InvA gene was investigated in all isolates, whereas the SdiA and Stn genes were observed in four and three isolates, respectively. Utilizing the disc diffusion method, S. typhimurium isolates demonstrated substantial resistance to most of the examined antibiotics with a high multiple antibiotic resistance index. S. typhimurium isolates demonstrated biofilm formation abilities to various degrees at varied temperatures levels (4 °C and 37 °C). In conclusion, the obtained samples from the research area are regarded as a potential S. typhimurium contamination source. Furthermore, garlic essential oil (GEO) has more potential to inhibit S. typhimurium biofilm at different sub-minimum inhibitory concentrations as compared to thyme essential oil (TEO). Therefore, these EOs are considered as potential natural antibacterial options that could be applied in food industry.

Salmonella spp. quorum sensing: an overview from environmental persistence to host cell invasion

Salmonella spp. is one of the main foodborne pathogens around the world. It has a cyclic lifestyle that combines host colonization with survival outside the host, implying that Salmonella has to adapt to different conditions rapidly in order to survive. One of these environments outside the host is the food production chain. In this environment, this foodborne pathogen has to adapt to different stress conditions such as acidic environments, nutrient limitation, desiccation, or biocides. One of the mechanisms used by Salmonella to survive under such conditions is biofilm formation. Quorum sensing plays an important role in the production of biofilms composed of cells from the same microorganism or from different species. It is also important in terms of food spoilage and regulates the pathogenicity and invasiveness of Salmonella by regulating Salmonella pathogenicity islands and flagella. Therefore, in this review, we will discuss the genetic mechanism involved in Salmonella quorum sensing, paying special attention to small RNAs and their post-regulatory activity in quorum sensing. We will further discuss the importance of this cell-to-cell communication mechanism in the persistence and spoilage of Salmonella in the food chain environment and the importance in the communication with microorganisms from different species. Subsequently, we will focus on the role of quorum sensing to regulate the virulence and invasion of host cells by Salmonella and on the interaction between Salmonella and other microbial species. This review offers an overview of the importance of quorum sensing in the Salmonella lifestyle.

Quorum-quenching activity of some Iranian medicinal plants

Anti-quorum sensing (QS) or quorum quenching (QQ) is known as a new anti-bacterial strategy to combat bacterial infection. One of the best candidates for this strategy is a natural plant or traditional herbal medicine. This review aimed to summarize and introduce Iranian medicinal plants with anti-QS properties. Biomedical databases (PubMed, Scopus, Google Scholar and Web of sciences) were investigated to retrieve all related manuscripts published in English and Persian. Out of 65 documents, 47 papers were published during 2010–2020. We categorized and summarized 19 papers that particularly presented the anti-QS activity of Iranian medicinal plants. Based on our results, different studies have been completed on the QQ effects of medicinal plants. We identified 106 plant species with different properties in medicine that have been evaluated for anti-QS activities in Iran. The QQ effects of herbal extracts were identified through different in vitro examinations on biosensor and clinical bacterial strains. Only 35 medicinal plants have shown these effects at sub-MICs. Our review summarizes Iranian medicinal plants with anti-QS properties. Some of these herbal extracts showed anti-QS activity against biosensors, standard and clinical bacterial strains. This result is very important because QS systems can be considered as a new target for the development of new remedial strategies and it is a good opportunity to perform QQ studies to effectively combat bacterial infections in the future.

A review on traditional uses, phytochemistry, pharmacology, and clinical research of dietary spice Cuminum cyminum L

Cuminum cyminum L. is a versatile spice belonging to family Apiaceae. Though the plant has pan-tropical distribution but it is indigenous to Egypt, the Mediterranean, and South Asian countries. It exhibits numerous culinary, traditional, and pharmacological attributes. Its traditional uses also validate its immense pharmacological potential. Cuminum cyminum is the hub of numerous bioactives such as alkaloids, flavonoids, terpenoids, and so forth. Cuminaldehyde is the major bioactive, rendered to most of its pharmacological as well as clinical significance. The present study comprised of current knowledge on its taxonomy, nutritional, traditional, phytochemistry, pharmacology (antimicrobial, antioxidant, anti-inflammation, antidiabetic, wound healing, anticancer, etc.), toxicology, and clinical attributes. Besides, the mechanism of action is also well explained. The present study provides a rationale for further bioprospection of this wonder plant. Future studies are needed to fill the research gaps, particularly on relevant phytocompound isolation, their pre-clinical and clinical characterization, evaluation, and structure-activity relationship. Moreover, well-designed and highly appropriate clinical and placebo trials are still needed to demonstrate the trustworthy role of cumin on human health.