**Barbara Speranza 1, Arcangelo Liso 2,\* , Vincenzo Russo <sup>3</sup> and Maria Rosaria Corbo 1,\***


Received: 29 November 2019; Accepted: 21 January 2020; Published: 25 January 2020

**Abstract:** This study proposes to exploit the in vivo metabolism of two probiotics (*Bifidobacterium longum* subsp. *infantis* and *Lactobacillus reuteri*) which, upon adhesion on a solid surface, form a biofilm able to control the growth of pathogenic and food spoilage bacteria. The results showed that pathogenic cell loads were always lower in presence of biofilm (6.5–7 log CFU/cm2) compared to those observed in its absence. For *Escherichia coli* O157:H7, a significant decrease (>1–2 logarithmic cycles) was recorded; for *Listeria monocytogenes*, *Staphylococcus aureus,* and *Salmonella enterica*, cell load reductions ranged from 0.5 to 1.5 logarithmic cycles. When tested as active packaging, the biofilm was successfully formed on polypropylene, polyvinyl chloride, greaseproof paper, polyethylene and ceramic; the sessile cellular load ranged from 5.77 log CFU/cm<sup>2</sup> (grease-proof paper) to 6.94 log CFU/cm<sup>2</sup> (polyethylene, PE). To test the potential for controlling the growth of spoilage microorganisms in food, soft cheeses were produced, inoculated with *L. monocytogenes* and *Pseudomonas fluorescens,* wrapped in PE pellicles with pre-formed biofim, packed both in air and under vacuum, and stored at 4 and 15 ◦C: an effective effect of biofilms in slowing the decay of the microbiological quality was recorded.

**Keywords:** probiotic; biofilm; pathogen; spoilage bacteria; active packaging
