Preparation of Laser-Ablated Ag Nanoparticle–MMT Clay-Based Beeswax Antibiofilm Coating

Abstract

Unlike other antimicrobial agents, Ag-based composites are stable and currently widely used as broad spectral additives, fighting microbial biofilms and other biological threats. The goal of the present study is to develop a green, multifunctional, and robust antibiofilm water-insoluble coating, inhibiting histamine-producing Lentilactobacillus parabuchneri biofilms. Herein, laser-ablated Ag NPs (L-Ag NPs) were incorporated into and onto a montmorillonite (MMT) surface layer with a simple wet chemical method, provided that the electrostatic interaction between L-Ag NPs and MMT clay led to the formation of L-Ag/MMT nanoantimicrobials (NAMs). The use of MMT support can facilitate handling Ag NPs in industrial applications. The Ag/MMT composite was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which confirmed the entrapment of L-Ag NPs into MMT clay. The surface chemical composition was assessed with X-ray photoelectron spectroscopy, proving that Ag NPs were in contact with and deposited onto the surface of MMT. The characteristic L-Ag/MMT band was investigated with UV–vis spectroscopy. Following that, the L-Ag/MMT composite was embedded into a biosafe water-insoluble beeswax agent with a spin coating technique. The antimicrobial ion release kinetic profile of the L-Ag/MMT/beeswax coating through an electrothermal atomic absorption spectroscopy (ETAAS) study supported the controlled release of Ag ions, reaching a plateau at 420 ±80 nM, which is safe from the point of view of Ag toxicity. Microbial biofilm growth inhibition was assessed with real-time in situ Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) in a flow cell assembly over 32 h. The study was further supported by optical density (OD) measurements and SEM on bacteria incubated in the presence of the L-Ag/MMT/beeswax coating.

Characterization of the Biofilms Formed by Histamine-Producing Lentilactobacillus parabuchneri Strains in the Dairy Environment

“…[ 13 , 65 , 66 ]. New materials that might prevent microbial growth are being explored [ 67 , 68 ], including the use of safe natural antimicrobial coating surfaces [ 69 ], but there remain many that are difficult to clean. The design requirements of equipment can also render effective cleaning and disinfection difficult [ 36 ].…”

Development of super nanoantimicrobials combining AgCl, tetracycline and benzalkonium chloride

“…Bacterial cells were maintained in De Man, Rogosa and Sharpe (MRS) broth in a microaerophilic environment during incubation at 37 °C for 24 h. At the end of the exponential growth phase, the OD 600 of the bacterial solutions was monitored using a UV–Vis spectrophotometer (Specord S600, Analytik Jena AG, Germany). Cells were resuspended in fresh MRS medium to reach OD 600 = 0.7 ready for in situ IR spectroscopy [ 32 ]. The strain was isolated at − 80 °C in MRS with 10% w / v sterile glycerol.…”

“…For the real-time monitoring of L. parabuchneri biofilm growth and inhibitions, experiments were performed by the use of a customized horizontal flow cell assembly, which consists of a removable top-plate and a trapezoidal horizontal 45° six-reflection ZnSe crystal with dimensions 72 × 10 × 6 mm [ 32 ]. The IR-inactive regions of the ATR element were covered by the spray-coating deposition of AgCl/BAC/TCH/PVMK nanoantimicrobial composite.…”

“…The identification of IR inactive regions on the ZnSe waveguide was described elsewhere [ 36 ]. The active sensing regions along the ATR element were in contact with biofilm formed inside the flow-cell, exposed only to the Ag + ions released by the neighboring regions (3 × 0.5 mm spots of nanoantimicrobials deposition, 0.5 mm thickness) [ 32 ]. The IR experiments for the long-term monitoring of biofilms were carried out separately: first, with a ZnSe crystal modified with the AgCl/BAC/TCH/PVMK coating; secondly, with a bare ZnSe waveguide.…”

“…IR signature of biofilms becomes apparent after 2 h from the beginning of the experiment, confirming the initial attachment has occurred. The associated increase of the related IR absorption features related to biofilm constituents such as amides and extracellular polymeric substances are distinct indicators of bacterial adhesion and L. parabuchneri biofilm growth [ 32 ]. The fresh MRS solution medium washed out the free cells that had not attached and delivered nutrients to the microorganisms.…”