Abstract
The present study aimed at the preparation of antimicrobial films based on low-density polyethylene (LDPE), with zeolite exchanged with Silver (Ag) in 1, 5 and 10 wt.%. Zeolites with Ag were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Fluorescence (XRF). LDPE films with added silver-substituted zeolite A were synthesized by wet-casting, with the zeolite content in the films ranging from 1–5 wt.%. The antibacterial activity of the silver-substituted zeolite was assessed according to its minimum inhibitory concentration (MIC), using Escherischia coli as the target bacteria. LDPE films with silver-loaded zeolite were also tested against E. coli and Staphylococcus aureus. Silver insertion in the zeolite did not change its structure. The MIC of the zeolite with 1% silver and a concentration of 0.05 mg zeolite/mL was not able to inhibit the visible growth of the bacteria; however, an increased silver concentration resulted in total inhibition after 24 h of incubation. Zeolites with 5% and 10% of silver showed a MIC of 0.05 mg zeolite/mL. The films with best antibacterial activity against E. coli and S. aureus were those prepared with 5 wt.% zeolites loaded with 5% and 10% of silver. LDPE films with silver-loaded zeolite A are potential resources in the development of active packaging for food preservation and safety.
Highlights
Metals have been widely applied in public health as antimicrobial agents [1], even before the clinical introduction of antibiotics in the 1940s [2]
The model microorganisms tested in the study of antimicrobial activity were strains of Escherichia coli
There was a clear decrease in peak intensity when an increasing silver content was incorporated into the zeolite
Summary
Metals have been widely applied in public health as antimicrobial agents [1], even before the clinical introduction of antibiotics in the 1940s [2]. Silver has been used for decades to inhibit pathogenic microorganisms in a range of areas [3]. Ionic silver has the highest antibacterial activity of all metal ions, and is widely used in topical medicines [4]. In addition to being broad spectrum antimicrobials, silver compounds, when used at appropriate concentrations, exhibit low mammalian cell toxicity [5]. Ionic silver is a Lewis acid with a high affinity to sulfur and nitrogen. In addition to damaging genetic material, silver ions react with ribosomes within the cytoplasm, directly affecting the expression of enzymes and proteins essential in the production of important substances for microorganisms [6,7,8]
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