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Abstract Elastomers such as silicone are common in medical devices (catheters, prosthetic implants, endoscopes), but they remain prone to microbial colonization and biofilm infections. For the first time, our work shows that rates of microbial surface attachment to polydimethylsiloxane (PDMS) silicone can be significantly affected by mechanical deformation. For a section of bent commercial catheter tubing, bacteria (P. aeruginosa) show a strong preference for the ‘convex’ side compared to the ‘concave’ side, by a factor of 4.2. Further testing of cast PDMS materials in bending only showed a significant difference for samples that were manually wiped (damaged) beforehand (1.75 × 104 and 6.02 × 103 cells/mm2 on the convex and concave sides, respectively). We demonstrate that surface microcracks in elastomers are opened under tensile stress (convex bending) to become ‘activated’ as sites for microbial colonization. This work demonstrates that the high elastic limit of elastomers enables these microcracks to reversibly open and close, as ‘dynamic defects’. Commercial catheters have relatively high surface roughness inherent to manufacturing, but we show that even manual wiping of newly-cast PDMS is sufficient to generate surface microcracks. We consider the implication for medical devices that feature sustained, surgical, or cyclic deformation, in which localized tensile conditions may expose these surface defects to opportunistic microbes. As a result, our work showcases serious potential problems in the widespread usage and development of elastomers in medical devices.

Abstract Pel exopolysaccharide biosynthetic loci are phylogenetically widespread biofilm matrix determinants in bacteria. In Pseudomonas aeruginosa, Pel is crucial for cell-to-cell interactions and reducing susceptibility to antibiotic and mucolytic treatments. While genes encoding glycoside hydrolases have long been linked to biofilm exopolysaccharide biosynthesis, their physiological role in biofilm development is unclear. Here we demonstrate that the glycoside hydrolase activity of P. aeruginosa PelA decreases adherent biofilm biomass and is responsible for generating the low molecular weight secreted form of the Pel exopolysaccharide. We show that the generation of secreted Pel contributes to the biomechanical properties of the biofilm and decreases the virulence of P. aeruginosa in Caenorhabditis elegans and Drosophila melanogaster. Our results reveal that glycoside hydrolases found in exopolysaccharide biosynthetic systems can help shape the soft matter attributes of a biofilm and propose that secreted matrix components be referred to as matrix associated to better reflect their influence.

With growing consumer awareness, exploitation of renewable resources is cost-effective and environment friendly. This work examines the potential of citrus peels as natural antioxidants and antimicrobials for food preservation. Extraction yield, total soluble phenols and flavonoids of various citrus peels (sweet orange, lemon, tangerine and grapefruit) were optimized by varying the solvent type. While the highest extract yield (~16 ​g/100g) was obtained from the sweet orange peels in methanol, extraction with ethanol maximized the concentration of total phenols and flavonoids (~80 ​mg catechol equivalents/100 ​g dry weight). In addition, sweet orange peel extract showed the highest DPPH, ABTS and hydroxyl radical scavenging values. UPLC-ESI-MS/MS analysis of aqueous and ethanolic extracts of sweet orange peels revealed more than 40 polyphenolic compounds including phenolic acids and flavonoids, some of which have not been previously reported. The predominant polyphenols were narirutin, naringin, hesperetin-7-O-rutinoside naringenin, quinic acid, hesperetin, datiscetin-3-O-rutinoside and sakuranetin. The incorporation of sweet orange peel extract into two vegetable oils enhanced their oxidative stability. In addition, all citrus peel extracts possessed high antimicrobial activity against several food-borne pathogens, and the activity was highest for the sweet orange peel extract. Overall results suggested the great potential of sweet orange peels as natural antioxidant and antimicrobials, which can be efficiently extracted using a simple and low-cost method, for enhancing the storage stability and safety of vegetable oils.

Fungal growth and mycotoxin production on foods and feeds cause poisoning and serious human diseases that may lead to death. Chemical preservatives and fungicides have negative impacts on both health and environment. In contrast, bio preservatives such as lactic acid bacteria (LAB) are effective, safe, biodegradable and have additional health benefits. Among 23 rod-shaped LAB strains that were isolated from Egyptian traditional fermented milk (Rayeb), strain RM1 showed the highest antifungal potency. Phylogenetic analysis based on complete 16S rRNA gene and unique phenotypic characteristics differentiated strain RM1 from the closely related Lactobacillus species suggesting it represents a novel species, for which the name Lactobacillus sp. RM1 is proposed. The cell-free supernatant (CFS) of Lactobacillus sp. RM1exhibited strong and broad antimicrobial activity against both toxigenic fungi and harmful bacteria. The chemical composition of CFS determined by GC–MS showed a wide variety of antioxidant and antimicrobial compounds. A complete inhibition of both aflatoxins B1 and ochratoxin A production was obtained at a CFS concentration of 15 mg/mL. When the CFS was used to treat wheat grains, the growth mycelia of Aspergillus parasiticus were completely inhibited after 2 weeks of incubation compared with untreated grains, which were covered with a mat of the fungus. The antifungal activity of Lactobacillus sp. RM1 against common toxigenic fungi, and its ability extend the shelf life of wheat grains prove its potential application as a natural preservative for food products. Keywords: Lactic acid bacteria, Lactobacillus sp. RM1, Mycotoxins, Antifungal, Fungal growth, Cell-free supernatant, HPLC, GC–MS