Adsorption of a biosurfactant on surfaces to enhance the disinfection of surfaces contaminated with Listeria monocytogenes

Nanocoating and its application as antimicrobials in the food industry: A review

Nanocoatings are ultra-thin layers on the nanoscale (<100 nm) that are deposited on the substrate to improve their properties and functionality. These nanocoatings provide significant advantages compared to traditional coating, including stain resistance, antimicrobial and antioxidant activities, odor control and delivery of active agents, and liquid repellence properties. In the food industry, nanocoating is widely used in the food packaging sector. In this regard, nanocoating offers antimicrobials and antioxidant properties to active food packaging by incorporating active bioactive compounds into materials used in already existing packaging. The application of nanocoating is applied to these kinds of food packaging with nano coating to improve shelf life, safety, and quality of food packaging. In smart/intelligent packaging, the active packaging coating is promising food packaging, which is designed by releasing preservatives and nanocoating as an antimicrobial, antifungal, antioxidant, barrier coating, and self-cleaning food contact surfaces. In addition, nanocoating can be used for food contact surfaces, kitchen utensils, and food processing equipment to create antimicrobial, antireflective, and dirt-repellent properties. These are critical properties for food processing, especially for meat and dairy processing facilities, which can reduce biofilm formation and prevent cross-contamination. Recently, appreciable growth in the development of the application of nanocoating as edible films for coating food products has emerged to improve food safety issues. In this regard, much scientific research in the area of nanocoating fruits and vegetables, and other food products was performed to address food safety issues. Hence, this promising technology can be a great addition to the agricultural and food industries. Thus, this review addresses the most relevant information about this technology and the applications of nanocoating in the food industry.

Determining the potential use of biosurfactants in preventing endodontic infections

Microbial biofilms play a dominant role in the failure of endodontic therapies. Bacterial adhesion is the first step in the establishment of biofilms, activating the host immune response leading to tissue damage. Biosurfactants are microbe-derived tensioactive molecules with latent anti-adhesive and anti-microbial activity. This study reports the extraction and characterization of a biosurfactant from Lactobacillus (L.) plantarum (Lp-BS) and investigates its anti-microbial and anti-adhesive properties compared to rhamnolipid, a commercially available biosurfactant. Lp-BS, extracted from L. plantarum during the growth phase, was characterized as a glycoprotein, able to reduce surface tension and emulsify non-polar liquids. Proteomic analysis of Lp-BS identified three bacterial adhesin-like proteins, suggesting roles in hindering bacterial adhesion. Lp-BS did not show significant anti-microbial activity against endodontic pathogens from the Streptococcus (Strep.) anginosus group or Enterococcus (Ent.) faecalis at 50 mg/ml. However, anti-adhesive activity on abiotic surfaces was observed against both Strep. anginosus and Strep. intermedius. Rhamnolipid exhibited strong anti-microbial activity, with minimum inhibitory concentrations of 0.097 mg/ml against Strep. anginosus, and 0.048 mg/ml against Strep. constellatus and Strep. intermedius, in addition to a marked anti-adhesive activity. These findings offer preliminary evidence for the potential application of biosurfactants as an anti-microbial and/or anti-adhesive pharmacotherapy in endodontics.

Metabolic Characterization of Supernatants Produced by Lactobacillus spp. With in vitro Anti-Legionella Activity

Legionella pneumophila is an organism of public health interest for its presence in water supply systems and other humid thermal habitats. In this study, ten cell-free supernatants produced by Lactobacillus strains were evaluated for their ability to inhibit L. pneumophila strains isolated from hot tap water. Production of antimicrobial substances by Lactobacillus strains were assessed by agar well diffusion test on BCYE agar plates pre-inoculated with L. pneumophila. Cell-free supernatants (CFS) showed antimicrobial activity against all Legionella strains tested: L. rhamnosus and L. salivarius showed the highest activity. By means of a proton-based nuclear magnetic resonance (¹H-NMR) spectroscopy, we detected and quantified the Lactobacillus metabolites of these CFSs, so to gain information about which metabolic pathway was likely to be connected to the observed inhibition activity. A panel of metabolites with variations in concentration were revealed, but considerable differences among inter-species were not showed as reported in a similar work by Foschi et al. (2018). More than fifty molecules belonging mainly to the groups of amino acids, organic acids, monosaccharides, ketones, and alcohols were identified in the metabolome. Significant differences were recorded comparing the metabolites found in the supernatants of strains grown in MRS with glycerol and the same strains grown in MRS without supplements. Indeed, pathway analysis revealed that glycine, serine and threonine, pyruvate, and sulfur metabolic pathways had a higher impact when strains were grown in MRS medium with a supplement such as glycerol. Among the metabolites identified, many were amino acids, suggesting the possible presence of bacteriocins which could be linked to the anti-Legionella activity shown by cell-free supernatants.

Using Photocatalyst Metal Oxides as Antimicrobial Surface Coatings to Ensure Food Safety-Opportunities and Challenges

Cross-contamination of foods with pathogenic microorganisms such as bacteria, viruses, and parasites may occur at any point in the farm to fork continuum. Food contact and nonfood contact surfaces are the most frequent source of microbial cross-contamination. In the wake of new and emerging food safety challenges, including antibiotic-resistant human pathogens, conventional sanitation and disinfection practices may not be sufficient to ensure safe food processing, proper preparation, and also not be environmentally friendly. Nanotechnology-enabled novel food safety interventions have a great potential to mitigate the risk of microbial cross-contamination in the food chain. Especially engineered nanoparticles (ENPs) are increasingly finding novel applications as antimicrobial agents. Among various ENPs, photocatalyst metal oxides have shown great promise as effective nontargeted disinfectants over a wide range of microorganisms. The present review provides an overview of antimicrobial properties of various photocatalyst metal oxides and their potential applications as surface coatings. Further, this review discusses the most common approaches to developing antimicrobial coatings, methods to characterize, test, and evaluate antimicrobial efficacy as well as the physical stability of the coatings. Finally, regulations and challenges concerning the use of these novel photocatalytic antimicrobial coatings are also discussed.

Corrosion of carbon steel induced by a microbial-enhanced oil recovery bacterium Pseudomonas sp. SWP-4

Pseudomonas sp. SWP-4 has been proved to enhance oil recovery effectively.

Co-culture with Listeria monocytogenes within a dual-species biofilm community strongly increases resistance of Pseudomonas putida to benzalkonium chloride

Biofilm formation is a phenomenon occurring almost wherever microorganisms and surfaces exist in close proximity. This study aimed to evaluate the possible influence of bacterial interactions on the ability of Listeria monocytogenes and Pseudomonas putida to develop a dual-species biofilm community on stainless steel (SS), as well as on the subsequent resistance of their sessile cells to benzalkonium chloride (BC) used in inadequate (sub-lethal) concentration (50 ppm). The possible progressive adaptability of mixed-culture biofilms to BC was also investigated. To accomplish these, 3 strains per species were left to develop mixed-culture biofilms on SS coupons, incubated in daily renewable growth medium for a total period of 10 days, under either mono- or dual-species conditions. Each day, biofilm cells were exposed to disinfection treatment. Results revealed that the simultaneous presence of L. monocytogenes strongly increased the resistance of P. putida biofilm cells to BC, while culture conditions (mono-/dual-species) did not seem to significantly influence the resistance of L. monocytogenes biofilm cells. BC mainly killed L. monocytogenes cells when this was applied against the dual-species sessile community during the whole incubation period, despite the fact that from the 2nd day this community was mainly composed (>90%) of P. putida cells. No obvious adaptation to BC was observed in either L. monocytogenes or P. putida biofilm cells. Pulsed field gel electrophoresis (PFGE) analysis showed that the different strains behaved differently with regard to biofilm formation and antimicrobial resistance. Such knowledge on the physiological behavior of mixed-culture biofilms could provide the information necessary to control their formation.

Purification and characterization of a surfactin-like molecule produced by Bacillus sp. H2O-1 and its antagonistic effect against sulfate reducing bacteria

Background

Bacillus sp. H2O-1, isolated from the connate water of a Brazilian reservoir, produces an antimicrobial substance (denoted as AMS H2O-1) that is active against sulfate reducing bacteria, which are the major bacterial group responsible for biogenic souring and biocorrosion in petroleum reservoirs. Thus, the use of AMS H2O-1 for sulfate reducing bacteria control in the petroleum industry is a promising alternative to chemical biocides. However, prior to the large-scale production of AMS H2O-1 for industrial applications, its chemical structure must be elucidated. This study also analyzed the changes in the wetting properties of different surfaces conditioned with AMS H2O-1 and demonstrated the effect of AMS H2O-1 on sulfate reducing bacteria cells.

Results

A lipopeptide mixture from AMS H2O-1 was partially purified on a silica gel column and identified via mass spectrometry (ESI-MS). It comprises four major components that range in size from 1007 to 1049 Da. The lipid moiety contains linear and branched β-hydroxy fatty acids that range in length from C13 to C16. The peptide moiety contains seven amino acids identified as Glu-Leu-Leu-Val-Asp-Leu-Leu.

Transmission electron microscopy revealed cell membrane alteration of sulfate reducing bacteria after AMS H2O-1 treatment at the minimum inhibitory concentration (5 μg/ml). Cytoplasmic electron dense inclusions were observed in treated cells but not in untreated cells. AMS H2O-1 enhanced the osmosis of sulfate reducing bacteria cells and caused the leakage of the intracellular contents. In addition, contact angle measurements indicated that different surfaces conditioned by AMS H2O-1 were less hydrophobic and more electron-donor than untreated surfaces.

Conclusion

AMS H2O-1 is a mixture of four surfactin-like homologues, and its biocidal activity and surfactant properties suggest that this compound may be a good candidate for sulfate reducing bacteria control. Thus, it is a potential alternative to the chemical biocides or surface coating agents currently used to prevent SRB growth in petroleum industries.

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.

Synergistic effect of lipopeptide biosurfactant with antibiotics against Escherichia coli CFT073 biofilm

Biofilms are microcolonies of microbes adherent to biotic and abiotic surfaces, often responsible for chronic infections and medical device contamination. Escherichia coli is one of the prevalent pathogens involved in uropathogenic infections and contamination of catheters. A biosurfactant produced by Bacillus licheniformis V9T14 was tested alone and in association with various antibiotics against a mature 24-h uropathogenic E. coli CFT073 biofilm. Biofilm was grown on polystyrene pegs of a Calgary Biofilm Device, providing a tool to evaluate the efficacy of antimicrobial agents. Antibiotics tested were ampicillin, cefazolin, ceftriaxone, ciprofloxacin, piperacillin, tobramycin and trimethoprim/sulfamethoxazole (19:1). Biosurfactant alone at the concentrations tested was not able to remove the adherent cells of the pre-formed biofilm. However, the difference between the effect of antibiotic alone and in combination with the biosurfactant was significant and exceeded 1log(10) (90%) reduction in most cases. Results of this study indicate that V9T14 biosurfactant in association with antibiotics leads to a synergistic increase in the efficacy of antibiotics in biofilm killing, and in some combinations leads to total eradication of E. coli CFT073 biofilm.

Microbial biosurfactants production, applications and future potential

Microorganisms synthesise a wide range of surface-active compounds (SAC), generally called biosurfactants. These compounds are mainly classified according to their molecular weight, physico-chemical properties and mode of action. The low-molecular-weight SACs or biosurfactants reduce the surface tension at the air/water interfaces and the interfacial tension at oil/water interfaces, whereas the high-molecular-weight SACs, also called bioemulsifiers, are more effective in stabilising oil-in-water emulsions. Biosurfactants are attracting much interest due to their potential advantages over their synthetic counterparts in many fields spanning environmental, food, biomedical, and other industrial applications. Their large-scale application and production, however, are currently limited by the high cost of production and by limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and the latest advances in biosurfactant applications and the biotechnological strategies being developed for improving production processes and future potential.

Impact on disinfection efficiency of cell load and of planktonic/adherent/detached state: case of Hafnia alvei inactivation by plasma activated water

This paper describes the effects of initial microbial concentration and planktonic/adherent/detached states on the efficiency of plasma-activated water. This disinfecting solution was obtained by treating distilled water with an atmospheric pressure plasma produced by gliding electric discharges in humid air. The inactivation kinetics of planktonic cells of Hafnia alvei (selected as a bacterial model) were found to be of the first order. They were influenced by the initial microbial concentration. Efficiency decreased when the initial viable population N(0) increased, and the inactivation rate k(max) was linearly modified as a function of Log(10) (N(0)). This relation was used to compare planktonic, adherent, and detached cells independently from the level of population. Bacteria adhering to stainless steel and high-density polyethylene were also sensitive to treatment, but at a lower rate than their free-living counterparts. Moreover, cells detached from these solid substrates exhibited an inactivation rate lower than that of planktonic cells but similar to adherent bacteria. This strongly suggests the induction of a physiological modification to bacteria during the adhesion step, rendering adherent--and further detached--bacteria less susceptible to the treatment, when compared to planktonic bacteria.