Development and characterization of anti-biofilm coatings applied by Non-Equilibrium Atmospheric Plasma on stainless steel

Hidden Places for Foodborne Bacterial Pathogens and Novel Approaches to Control Biofilms in the Meat Industry

Biofilms are of great concern for the meat industry because, despite the implementation of control plans, they remain important hotspots of contamination by foodborne pathogens, highlighting the need to better understand the ecology of these microecosystems. The objective of this paper was to critically survey the recent scientific literature on microbial biofilms of importance for meat safety and quality, also pointing out the most promising methods to combat them. For this, the databases PubMed, Scopus, Science Direct, Web of Science, and Google Scholar were surveyed in a 10-year time frame (but preferably papers less than 5 years old) using selected keywords relevant for the microbiology of meats, especially considering bacteria that are tolerant to cleaning and sanitization processes. The literature findings showed that massive DNA sequencing has deeply impacted the knowledge on the species that co-habit biofilms with important foodborne pathogens (Listeria monocytogenes, Salmonella, pathogenic Escherichia coli, and Staphylococcus aureus). It is likely that recalcitrant commensal and/or spoilage microbiota somehow protect the more fastidious organisms from harsh conditions, in addition to harboring antimicrobial resistance genes. Among the members of background microbiota, Pseudomonas, Acinetobacter, and Enterobacteriales have been commonly found on food contact and non-food contact surfaces in meat processing plants, in addition to less common genera, such as Psychrobacter, Enhydrobacter, Brevundimonas, and Rothia, among others. It has been hypothesized that these rare taxa may represent a primary layer in microbial biofilms, offering better conditions for the adhesion of otherwise poor biofilm formers, especially considering their tolerance to cold conditions and sanitizers. Taking into consideration these findings, it is not only important to target the foodborne pathogens per se in cleaning and disinfection plans but the use of multiple hurdles is also recommended to dismantle the recalcitrant structures of biofilms. In this sense, the last part of this manuscript presents an updated overview of the antibiofilm methods available, with an emphasis on eco-friendly approaches.

Antibiofilm Activity of PDMS/TiO2 against Candida glabrata through Inhibited Hydrophobic Recovery

Coatings with antibiofilm properties are desirable for biomedical applications. Titanium dioxide (TiO2) has been explored as an antimicrobial agent in materials development primarily due to it being an excellent photocatalyst. Candida glabrata (C. glabrata) is an emerging human fungal pathogen with known high resistance to oxidative stress. Here, we fabricated a polydimethylsiloxane/titanium dioxide (PDMS/TiO2) nanocomposite coating and tested its antibiofilm activities against C. glabrata. The resulting nanocomposite exhibited >50% reduction in C. glabrata biofilm formation with 2.5 wt % TiO2 loading, even in the dark. Through ROS detection and surface characterization, the antibiofilm activity was attributed to the synergistic interaction of TiO2 nanoparticles with the PDMS matrix, which resulted in the impediment of hydrophobic recovery. This work provides a design strategy to develop antibiofilm coatings against C. glabrata.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Critical analysis of methods to determine growth, control and analysis of biofilms for potential non-submerged antibiofilm surfaces and coatings

The potential uses for antibiofilm surfaces reach across different sectors with significant resultant economic, societal and health impact. For those interested in using antibiofilm surfaces in the built environment, it is important that efficacy testing methods are relevant, reproducible and standardised where possible, to ensure data outputs are applicable to end-use, and comparable across the literature. Using pre-defined keywords, a review of literature reporting on antimicrobial surfaces (78 articles), within which a potential application was described as non-submerged/non-medical surface or coating with antibiofilm action, was undertaken. The most used methods utilized the growth of biofilm in submerged and static systems. Quantification varied (from most to least commonly used) across colony forming unit counts, non-microscopy fluorescence or spectroscopy, microscopy analysis, direct agar-contact, sequencing, and ELISA. Selection of growth media, microbial species, and incubation temperature also varied. In many cases, definitions of biofilm and attempts to quantify antibiofilm activity were absent or vague. Assessing a surface after biofilm recovery or assessing potential regrowth of a biofilm after initial analysis was almost entirely absent. It is clear the field would benefit from widely agreed and adopted approaches or guidance on how to select and incorporate end-use specific conditions, alongside minimum reporting guidelines may benefit the literature.

A Review of Antimicrobial Polymer Coatings on Steel for the Food Processing Industry

This article will focus on the issue of protection against the pathogenic biofilm development on steel surfaces within the food sectors, highlighting steel's prominence as a material choice in these areas. Pathogenic microorganism-based biofilms present significant health hazards in the food industry. Current scientific research offers a variety of solutions to the problem of protecting metal surfaces in contact with food from the growth of pathogenic microorganisms. One promising strategy to prevent bacterial growth involves applying a polymeric layer to metal surfaces, which can function as either an antiadhesive barrier or a bactericidal agent. Thus, the review aims to thoroughly examine the application of antibacterial polymer coatings on steel, a key material in contact with food, summarizing research advancements in this field. The investigation into polymer antibacterial coatings is organized into three primary categories: antimicrobial agent-releasing coatings, contact-based antimicrobial coatings, and antifouling coatings. Antibacterial properties of the studied types of coatings are determined not only by their composition, but also by the methods for applying them to metal and coating surfaces. A review of the current literature indicates that coatings based on polymers substantially enhance the antibacterial properties of metallic surfaces. Furthermore, these coatings contribute additional benefits including improved corrosion resistance, enhanced aesthetic appeal, and the provision of unique design elements.

Impact of lactic acid bacteria strains against Listeria monocytogenes biofilms on various food-contact surfaces

Listeria monocytogenes is one of the most important foodborne pathogens, causing listeriosis, a disease characterized by high mortality rates. This microorganism, commonly found in food production environments and transmitted to humans by consuming contaminated food, has the ability to form biofilms by attaching to a wide variety of surfaces. Traditional hygiene and sanitation procedures are not effective enough to completely remove L. monocytogenes biofilms from food-contact surfaces, which makes them a persistent threat to food safety. Alternative approaches to combating Listeria biofilms are needed, and the use of lactic acid bacteria (LAB) and their antimicrobial compounds shows promise. The present study investigated the effect of Lactobacillus strains, previously isolated from various foods and known to possess antimicrobial properties, on the biofilm formation of L. monocytogenes on three different food-contact surfaces. To study L. monocytogenes IVb ATCC 19115 type, culture was preferred to represent serotype IVb, which is responsible for the vast majority of listeriosis cases. The results demonstrated that cell-free supernatants (CFSs) of LAB strains inhibited biofilm formation by up to 51.57% on polystyrene, 60.96% on stainless steel, and 30.99% on glass surfaces. Moreover, these CFSs were effective in eradicating mature biofilms, with reductions of up to 78.86% on polystyrene, 73.12% on stainless steel, and 72.63% on glass surfaces. The strong inhibition rates of one strain of L. curvatus (P3X) and two strains of L. sakei (8.P1, 28.P2) used in the present study imply that they may provide an alternate technique for managing Listeria biofilms in food production environments.

Durable superhydrophobic coatings for stainless-steel: An effective defense against Escherichia coli and Listeria fouling in the post-harvest environment

Increasing concerns revolve around bacterial cross-contamination of leafy green vegetables via food-contact surfaces. Given that stainless-steel is among the commonly used food-contact surfaces, this study reports a coating strategy enhancing its hygiene and microbiological safety through an antifouling approach via superhydrophobicity. The developed method involves growing a nickel-nanodiamond nanocomposite film on 304 stainless-steel via electroplating and sequential functionalization of the outer surface layer with nonpolar organosilane molecules via polydopamine moieties. The resultant superhydrophobic stainless-steel surfaces had a static water contact angle of 156.3 ± 1.9° with only 2.3 ± 0.5° contact angle hysteresis. Application of the coating to stainless-steel was demonstrated to yield 2.3 ± 0.6 log10 and 2.0 ± 0.9 log10 reductions in the number of adherent gram-negative Escherichia coli O157:H7 and gram-positive Listeria innocua cells, respectively. These population reductions were shown to be statistically significant (α = 0.05). Coated stainless-steel also resisted fouling when contacted with contaminated romaine lettuce leaves and maintained significant non-wetting character when abraded with sand or contacted with high concentration surfactant solutions. The incorporation of superhydrophobic stainless-steel surfaces into food processing equipment used for washing and packaging leafy green vegetables has the potential to mitigate the transmission of pathogenic bacteria within food production facilities.

The background microbiota and sanitization agent drive the fate of Listeria monocytogenes in multispecies biofilms formed on a plasma-polymerized coating applied on stainless steel

The present study evaluates the anti-biofilm activity of a coating applied with an atmospheric-pressure plasma jet system on AISI 316 stainless steel (SS) against multispecies biofilms containing Listeria monocytogenes (using background microbiota from three different meat industries) using culture-dependent and culture-independent approaches. Also, the disinfection effectiveness and biofilm evolution after sanitization with two food industry biocides were assessed. The anti-biofilm activity of the coating against L. monocytogenes, observed on mono-species biofilms (p < 0.05), was lost on the multispecies biofilms developed for 7 days at 12 °C (p > 0.05), with L. monocytogenes counts ranging from 5.5 ± 0.7 to 6.1 ± 0.5 CFU/cm² on the uncoated SS and from 4.4 ± 0.2 to 6.4 ± 0.5 CFU/cm² on the coated SS. The taxonomic composition of the formed biofilms was highly dependent on the industry but not affected by the artificial inoculation with L. monocytogenes and the nature of the surface (coated vs uncoated SS). When L. monocytogenes was artificially inoculated, its growth was partially controlled in the biofilms developed, with the magnitude of this effect being lower (p < 0.05 on coated SS) for the industry with the lowest taxonomy richness and diversity (3.8 ± 0.2 CFU/cm²), as compared the other two sampled industries (2.4 ± 0.4 and 1.6 ± 0.2 CFU/cm²). The 15-min disinfection treatments with either sodium hypochlorite or peracetic acid at 0.5 % resulted in total viable and L. monocytogenes counts below the limit of detection in most cases, immediately after treatment. The subsequent incubation of the sanitized plates for another 7 days at 12 °C in fresh BHI media led to the development of biofilms with lower bacterial richness and alpha diversity, and higher beta diversity. Even though sodium hypochlorite was in general slightly less effective than peracetic acid immediately after application, it caused a stronger growth control (p < 0.05) of the naturally present L. monocytogenes on the multispecies biofilms developed. This finding highlights the importance of understanding the interspecific competitive relationships between the members of the background microbiota and L. monocytogenes for the long-term control of this pathogen in food processing facilities.

Cold plasma surface treatments to prevent biofilm formation in food industries and medical sectors

Environmental conditions in food and medical fields enable the bacteria to attach and grow on surfaces leading to resistant bacterial biofilm formation. Indeed, the first step in biofilm formation is the bacterial irreversible adhesion. Controlling and inhibiting this adhesion is a passive approach to fight against biofilm development. This strategy is an interesting path in the inhibition of biofilm formation since it targets the first step of biofilm development. Those pathogenic structures are responsible for several foodborne diseases and nosocomial infections. Therefore, to face this public health threat, researchers employed cold plasma technologies in coating development. In this review, the different factors influencing the bacterial adhesion to a substrate are outlined. The goal is to present the passive coating strategies aiming to prevent biofilm formation via cold plasma treatments, highlighting antiadhesive elaborated surfaces. General aspects of surface treatment, including physico-chemical modification and application of cold plasma technologies, were also presented. KEY POINTS: • Factors surrounding pathogenic bacteria influence biofilm development. • Controlling bacterial adhesion prevents biofilm formation. • Materials can be coated via cold plasma to inhibit bacterial adhesion.

Durability Assessment of a Plasma-Polymerized Coating with Anti-Biofilm Activity against L. monocytogenes Subjected to Repeated Sanitization

Biofilm formation on food-contact surfaces is a matter of major concern causing food safety and spoilage issues to this sector. The aim of this study was to assess the durability of the anti-biofilm capacity of a plasma-polymerized coating composed of a base coating of (3-aminopropyl)triethoxysilane (APTES) and a functional coating of acrylic acid (AcAc). Coated and uncoated AISI 316 stainless steel (SS) plates were subjected to five sanitization cycles with sodium hypochlorite (0.05%) and peracetic acid (0.5%). The effectiveness of the coating for the inhibition of multi-strain Listeria monocytogenes biofilm formation was confirmed using a three-strain cocktail, which was grown on the SS plates at 12 °C for 6 days. Compared to the uncoated SS, relative biofilm productions of 14.6% on the non-sanitized coating, 27.9% on the coating after sanitization with sodium hypochlorite, and 82.3% on the coating after sanitization with peracetic acid were obtained. Morphological and physicochemical characterization of the coatings suggested that the greater anti-biofilm effectiveness after sanitization with sodium hypochlorite was due to the high pH of this solution, which caused a deprotonation of the carboxylic acid groups of the functional coating. This fact conferred it a strong hydrophilicity and negatively charged its surface, which was favorable for preventing bacterial attachment and biofilm formation.