Bacterial Inactivation by Using Plastic Materials Activated with Combinations of Natural Antimicrobials

Irene Ortega Blázquez,Rosario Lucas,Antonio Gálvez,María Grande Burgos,Rubén Pérez Pulido

doi:10.3390/coatings8120460

Abstract

Natural antimicrobials have gained interest as possible inhibitors of biofilm formation. The aim of the present study was to determine the efficacy of antimicrobials derived from essential oils (carvacrol, thymol) plus bacteriocin AS-48 immobilized on two plastic supports (low density polyethylene and polyethylene–polyamide films) on bacterial inactivation. The polyethylene–polyamide vacuum-packaging plastic film activated with a combination of thymol plus enterocin AS-48 was the most effective in reducing the concentrations of viable planktonic and sessile cells for Listeria innocua, Lactobacillus fructivorans, Bacillus coagulans, and Bacillus licheniformis. Results from the study highlight the potential of polyethylene–polyamide film activated with thymol plus enterocin AS-48 for reducing the viable cell concentrations of spoilage Gram-positive bacteria and Listeria in both planktonic and sessile states.

Highlights

Biofilms are defined as microbial communities embedded in a polysaccharide matrix formed at the interface between a solid surface and the fluid that surrounds it [1]
The process of biofilm formation has been studied in detail, and it has been found that, in most cases, it passes through a series of stages that comprise the initial binding of the bacteria to the substrate in a labile manner, followed by an irreversible binding, in which adherent molecules are involved formation of microcolonies, maturation of the biofilm, and, dispersion of planktonic cells from the mature biofilm [3,4]
The plastic materials, Low-density polyethylene (LDPE) and PEA, and the concentrations of antimicrobials used in this study, were selected from preliminary trials in which squares prepared from different commercially available plastic films were activated with carvacrol, thymol, enterocin AS-48, and their combinations, at different concentrations, and deposited on bacterial lawns and further inspected by growth inhibition measured from the edge of the plastic squares

Summary

Introduction

Biofilms are defined as microbial communities embedded in a polysaccharide matrix formed at the interface between a solid surface and the fluid that surrounds it [1]. Biofilms show increased resistance to disinfection processes used in the food industry [2], and are persistent sources of contamination due to the release of planktonic cells and detachment of biofilm portions by mechanical forces. The process of biofilm formation has been studied in detail, and it has been found that, in most cases, it passes through a series of stages that comprise the initial binding of the bacteria to the substrate in a labile manner, followed by an irreversible binding, in which adherent molecules are involved formation of microcolonies, maturation of the biofilm, and, dispersion of planktonic cells from the mature biofilm [3,4]. Several strategies have been proposed for the control of biofilm formation, such as the use of bacteriocins, bacteriophages, or antimicrobial compounds of diverse nature [5,6,7].

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