Effect of the presence of titania nanoparticles in the development of Pseudomonas fluorescens biofilms on LDPE

Abstract

In this study the use of TiO₂ nanoparticles in the preparation of active packaging film materials is investigated. High energy ball milling was used to uniformly disperse TiO₂ nanoparticles within low density polyethylene, LDPE. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used to characterize the nanocomposites. Growth of Pseudomonas fluorescens and subsequent bio-film formation on the surfaces of LDPE with and without TiO₂ nanoparticles were studied with Atomic Force Microscopy (AFM) and viable cell counts. A set of samples placed either face down or face-up in microwell plates were subsequently immersed in P. fluorescens cultures and incubated for up to 48 h at 4 or 30 °C. AFM images showed that the presence of titania nanoparticles affects the growth, size, distribution and arrangement of bacteria on the polymer surfaces. Cell recovery and counting experiments revealed a reduction of at least 1-log (i.e. 90% reduction) in bacterial colony forming units per square centimeter (CFU cm⁻²) for the TiO₂ nanofilled polymer compared to LDPE films, without photoactivation. In the presence of TiO₂ nanoparticles, bacterial cells attached to the surfaces formed tight aggregates with apparently minor amounts of “extracellular polymer substances” (EPS) around them.