Study of nisin adsorption on plasma-treated polymer surfaces for setting up materials with antibacterial properties

Highly active nisin coated polycaprolactone electrospun fibers against both Staphylococcus aureus and Pseudomonas aeruginosa

In this study, a wound dressing of electrospun polycaprolactone (PCL) fibers incorporating the antimicrobial peptide (AMP) nisin was fabricated. Nisin was physically adsorbed to the PCL fibers and tested for antibacterial activity against both Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa). The PCL fibers had an average diameter of 1.16 μm ± 0.42 μm and no significant change in diameter occurred after nisin adsorption. X-ray photoelectron spectroscopy (XPS) analysis of the fibers detected nitrogen indicative of adsorbed nisin and the signal was used to quantify the levels of coverage on the fiber surfaces. In vitro nisin release studies showed a burst release profile with 80 % of the nisin being released from the fibers within 30 min. Air plasma pre-treatment of the PCL fibers to render them hydrophilic improved nisin loading and release. Antibacterial testing was performed using minimum inhibitory concentration (MIC) and surface attachment assays. The released nisin remained active against both Gram positive S. aureus and Gram negative P. aeruginosa, which has previously been difficult to achieve with single polymer fiber systems. Mammalian cell culture of the nisin coated fibers with L-929 mouse fibroblasts and human epidermal keratinocytes (HEKa) showed that the nisin did not have a significant effect on the biocompatibility of the PCL fibers. The results presented here demonstrate that the physical adsorption, which is a post-treatment, overcomes the potential limitations of harsh chemicals and fabrication conditions of electrospinning from organic solvents and provides a drug loading system having effective antibacterial properties in wound dressings.

Assessment of prerequisite programs implementation at food packaging manufacturing companies and hygiene status of food packaging in a developing country: Cross-sectional study

Food packaging has a critical role in all food types and along the food chain from product preservation to transportation, distribution, storage, retailing, and end-use. However, it can become a source of contamination and transfer of microorganisms to the packed food when its hygienic status is not well maintained. The aim of this study was to evaluate the Prerequisite programs (PRPs) implementation in 5 food packaging companies across Mount Lebanon through on-site inspections and to assess the compliance of contact surfaces, employee hands and packaging materials to microbiological specifications. Following on-site inspection, none of the companies achieved a full total score of 100% and scores ranged from 25 to 62%. Regarding the assessment of hygienic status of contact surfaces, non-conforming results (acceptable limit ≤0.6 log colony forming units (CFU)/cm2) were observed in 50% (5/10) of the surfaces for total viable count (TVC). For the employee hands, none of the hand swab samples (10/10) was conforming for TVC that was present in all samples above the acceptable limit. Highest and lowest reported values were 4.4 and 1.7 log CFU/hands respectively. For packaging samples collected during on-site inspections, TVC and yeasts and molds were detected in 20% (2/10) of the samples. However, the samples collected from the retail market, had higher contamination rates of 95% (19/20) and 65% (13/20) for TVC and yeasts and molds, respectively. As for Enterobacteriaceae, it was not detected in all tested contact surfaces, employees' hands, and packaging samples. PRPs assessment and related verification activities showed the need for companies to strengthen their hygienic programs and highlighted the importance of food safety management systems (FSMS) implementation not only in food companies but also in food packaging companies. Additionally, the effectiveness of PRPs implementation should be assessed on planned routine basis.

Effect of Cold Plasma Treatment on the Packaging Properties of Biopolymer-Based Films: A Review

Biopolymers, like polysaccharides and proteins, are sustainable and green materials with excellent film-forming potential. Bio-based films have gained a lot of attention and are believed to be an alternative to plastics in next-generation food packaging. Compared to conventional plastics, biopolymers inherently have certain limitations like hydrophilicity, poor thermo-mechanical, and barrier properties. Therefore, the modification of biopolymers or their films provide an opportunity to develop packaging materials with desired characteristics. Among different modification approaches, the application of cold plasma has been a very efficient technology to enhance the functionality and interfacial characteristics of biopolymers. Cold plasma is biocompatible, shows uniformity in treatment, and is suitable for heat-sensitive components. This review provides information on different plasma generating equipment used for the modification of films and critically analyses the impact of cold plasma on packaging properties of films prepared from protein, polysaccharides, and their combinations. Most studies to date have shown that plasma treatment effectively enhances surface characteristics, mechanical, and thermal properties, while its impact on the improvement of barrier properties is limited. Plasma treatment increases surface roughness that enables surface adhesion, ink printability, and reduces the contact angle. Plasma-treated films loaded with antimicrobial compounds demonstrate strong antimicrobial efficacy, mainly due to the increase in their diffusion rate and the non-thermal nature of cold plasma that protects the functionality of bioactive compounds. This review also elaborates on the existing challenges and future needs. Overall, it can be concluded that the application of cold plasma is an effective strategy to modify the inherent limitations of biopolymer-based packaging materials for food packaging applications.

Combined Antimicrobial Effect of Bio-Waste Olive Leaf Extract and Remote Cold Atmospheric Plasma Effluent

A novel strategy involving Olive Leaf Extract (OLE) and Cold Atmospheric Plasma (CAP) was developed as a green antimicrobial treatment. Specifically, we reported a preliminary investigation on the combined use of OLE + CAP against three pathogens, chosen to represent medical and food industries (i.e., E. coli, S. aureus and L. innocua). The results indicated that a concentration of 100 mg/mL (total polyphenols) in OLE can exert an antimicrobial activity, but still insufficient for a total bacterial inactivation. By using plain OLE, we significantly reduced the growth of Gram positive S. aureus and L. innocua, but not Gram-negative E. coli. Instead, we demonstrated a remarkable decontamination effect of OLE + CAP in E. coli, S. aureus and L. innocua samples after 6 h. This effect was optimally maintained up to 24 h in S. aureus strain. E. coli and L. innocua grew again in 24 h. In the latter strain, OLE alone was most effective to significantly reduce bacterial growth. By further adjusting the parameters of OLE + CAP technology, e.g., OLE amount and CAP exposure, it could be possible to prolong the initial powerful decontamination over a longer time. Since OLE derives from a bio-waste and CAP is a non-thermal technology based on ionized air, we propose OLE + CAP as a potential green platform for bacterial decontamination. As a combination, OLE and CAP can lead to better antimicrobial activity than individually and may replace or complement conventional thermal procedures in food and biomedical industries.

Functionalization of Crosslinked Sodium Alginate/Gelatin Wet-Spun Porous Fibers with Nisin Z for the Inhibition of Staphylococcus aureus-Induced Infections

Nisin Z, an amphipathic peptide, with a significant antibacterial activity against Gram-positive bacteria and low toxicity in humans, has been studied for food preservation applications. Thus far, very little research has been done to explore its potential in biomedicine. Here, we report the modification of sodium alginate (SA) and gelatin (GN) blended microfibers, produced via the wet-spinning technique, with Nisin Z, with the purpose of eradicating Staphylococcus aureus-induced infections. Wet-spun SAGN microfibers were successfully produced at a 70/30% v/v of SA (2 wt%)/GN (1 wt%) polymer ratio by extrusion within a calcium chloride (CaCl₂) coagulation bath. Modifications to the biodegradable fibers' chemical stability and structure were then introduced via crosslinking with CaCl₂ and glutaraldehyde (SAGNCL). Regardless of the chemical modification employed, all microfibers were labelled as homogeneous both in size (≈246.79 µm) and shape (cylindrical and defect-free). SA-free microfibers, with an increased surface area for peptide immobilization, originated from the action of phosphate buffer saline solution on SAGN fibers, were also produced (GNCL). Their durability in physiological conditions (simulated body fluid) was, however, compromised very early in the experiment (day 1 and 3, with and without Nisin Z, respectively). Only the crosslinked SAGNCL fibers remained intact for the 28 day-testing period. Their thermal resilience in comparison with the unmodified and SA-free fibers was also demonstrated. Nisin Z was functionalized onto the unmodified and chemically altered fibers at an average concentration of 178 µg/mL. Nisin Z did not impact on the fiber's morphology nor on their chemical/thermal stability. However, the peptide improved the SA fibers (control) structural integrity, guaranteeing its stability for longer, in physiological conditions. Its main effect was detected on the time-kill kinetics of the bacteria S. aureus. SAGNCL and GNCL loaded with Nisin Z were capable of progressively eliminating the bacteria, reaching an inhibition superior to 99% after 24 h of culture. The peptide-modified SA and SAGN were not as effective, losing their antimicrobial action after 6 h of incubation. Bacteria elimination was consistent with the release kinetics of Nisin Z from the fibers. In general, data revealed the increased potential and durable effect of Nisin Z (significantly superior to its free, unloaded form) against S. aureus-induced infections, while loaded onto prospective biomedical wet-spun scaffolds.

Invited review: Advances in nisin use for preservation of dairy products

Dairy product safety is a global public health issue that demands new approaches and technologies to control foodborne pathogenic microorganisms. Natural antimicrobial agents such as nisin can be added to control the growth of pathogens of concern in dairy foods, namely Listeria monocytogenes and Staphylococcus aureus. However, several factors affect the antimicrobial efficacy of nisin when directly added into the food matrix such as lack of stability at neutral pH, interaction with fat globules, casein, and divalent cations. To overcome these limitations, new and advanced strategies are discussed including nisin encapsulation technology, addition to active packaging, bioengineering, and combination with other antimicrobials. This review highlights advanced technologies with potential to expand and improve the use of nisin as a dairy preservative.

Nisin infusion into surface cracks in oxide coatings to create an antibacterial metallic surface

The efficacy of surface topology and chemistry on the ability for a surface to retain antimicrobial performance via the immobilization of a peptide was evaluated. A nanosecond pulsed laser was used to create oxide films on Ti-6Al-4V and 304L stainless steel. The laser conditions employed created a mudflat cracked surface on titanium, but no cracks on the steel. An antimicrobial peptide, nisin, was infused into the cracked and uncracked oxide surfaces to provide antimicrobial activity against Gram-positive bacteria; Listeria monocytogenes was chosen as the model microorganism. Release tests in distilled water at room temperature show that nisin is slowly liberated from the uncracked stainless steel surface, while there was no evidence of nisin liberation from the cracked titanium alloy surfaces, likely due to immobilization of the peptide into the artificially created micro-cracks on the surface of this alloy. Surfaces treated with nisin became active and exhibit anti-microbial performance against L. monocytogenes; this behavior is mostly retained after scrubbing/washing and simple immersion in water.

Food Safety through Natural Antimicrobials

Microbial pathogens are the cause of many foodborne diseases after the ingestion of contaminated food. Several preservation methods have been developed to assure microbial food safety, as well as nutritional values and sensory characteristics of food. However, the demand for natural antimicrobial agents is increasing due to consumers' concern on health issues. Moreover, the use of antibiotics is leading to multidrug resistant microorganisms reinforcing the focus of researchers and the food industry on natural antimicrobials. Natural antimicrobial compounds from plants, animals, bacteria, viruses, algae and mushrooms are covered. Finally, new perspectives from researchers in the field and the interest of the food industry in innovations are reviewed. These new approaches should be useful for controlling foodborne bacterial pathogens; furthermore, the shelf-life of food would be extended.

Linker-free covalent immobilization of nisin using atmospheric pressure plasma induced grafting

The linker-free covalent immobilization of polymers on surfaces has the potential to impart new properties and functions to surfaces for a wide range of applications. However, most current methods for the production of these surfaces involve multiple chemical steps and do not have a high degree of control over the chemical functionalities at the surface. A comprehensive study detailing the facile two-step covalent grafting of the antimicrobial peptide nisin onto polystyrene surfaces is reported. Functionalization is achieved using an atmospheric pressure plasma jet, and the reaction is monitored and compared with a standard wet chemical functionalization approach using a variety of analytical techniques. The reactive species produced by the atmospheric pressure plasma jet were analyzed by mass spectrometry and optical emission spectroscopy. The surface chemistry and topography of the functionalized surfaces were determined using contact angle measurements, Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy and atomic force microscopy respectively. Following surface analysis, the antimicrobial efficacy of the covalently grafted nisin against two major food borne pathogens (Staphylococcus aureus and Listeria monocytogenes) was assessed at two different pHs. The results demonstrated that a post-plasma treatment step after nisin deposition is required to covalently graft the peptide onto the surface. The covalent immobilization of nisin resulted in a significant reduction in bacterial counts within a short 30 minutes contact time. These surfaces were also significantly more antimicrobial compared to those prepared via a more traditional wet chemical approach indicating that the reported method could be a less expensive and less time consuming alternative.

Biocompatibility of plasma-treated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanofiber mats modified by silk fibroin for bone tissue regeneration

The objective of this study was to produce biocompatible plasma-treated and silk-fibroin (SF) modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofiber mats. The mats were plasma-treated using O2 or N2 gas to increase their hydrophilicity followed by SF immobilization for the improvement of biocompatibility. Contact angle measurements and SEM showed increased hydrophilicity and no disturbed morphology, respectively. Cell proliferation assay revealed that SF modification together with N2 plasma (PS/N2) promoted higher osteoblastic (SaOs-2) cell viability. Although, O2 plasma triggered more mineral formation on the mats, it showed poor cell viability. Consequently, the PS/N2 nanofiber mats would be a potential candidate for bone tissue engineering applications.

Kinetics and functional effectiveness of nisin loaded antimicrobial packaging film based on chitosan/poly(vinyl alcohol)

The aim of this study was to evaluate the kinetics and functional effectiveness of Nisin loaded chitosan/poly(vinyl alcohol) (Nisin-CS/PVA) as an antibacterial packaging film. The films were prepared by coating method and Staphylococcus aureus (S. aureus, ATCC6538) was used as test bacterium. The intermolecular hydrogen bonds between CS and PVA molecules were confirmed. The elasticity of films was significantly improved by the incorporation of PVA, and the film could also bear a relative high tensile strength at 26.7 MPa for CS/PVA=1/1. As CS/PVA ratio decreased, the water vapor permeability (WVP) decreased and reached its minimum value 0.983 × 10(-10)gm(-1)s(-1) at CS/PVA=1/1, meanwhile, oxygen permeability (OP) increased but still lower than 0.91 cm(3) μm m(-2)d(-1)kPa(-1) for CS/PVA=1/1 as the CS/PVA ratio was above 1:1. The initial diffusion of nisin (Mt/M ∞ < 2/3) from CS/PVA film could be well described by the Fickian diffusion equation. Owing to the positively charged nisin at pH below isoelectric point (pI, 8.8) and its increasing dissolubility in water as the pH reduced, the diffusion of nisin from the films strongly depended on pH and ionic strength besides CS/PVA ratio and temperature. Moreover, the thermodynamic parameters suggested the spontaneous and endothermic diffusion of nisin from the films. The resulting data can provide some valuable information for the design of film in structure and ingredient.

Rhamnolipid biosurfactant adsorption on a plasma-treated polypropylene surface to induce antimicrobial and antiadhesive properties

A glycolipid type of biosurfactant (rhamnolipid), which is obtained fromPseudomonas aeruginosaMA01, was adsorbed on a polypropylene film to produce an antimicrobial and antiadhesive polymeric surface for the first time.