Effects of Bacteriophage P100 at Different Concentrations on the Structural Parameters of Listeria monocytogenes Biofilms.

Because listeriosis is one of the deadliest foodborne diseases, controlling and eradicating Listeria monocytogenes biofilms is a serious challenge for food safety. Biofilms (24 h old) formed on polystyrene by a L. monocytogenes strain of food origin were exposed for a further 24 h to 12 different concentrations (from 100 to 1011 PFU/mL) of the bacteriophage P100 (Listex P100). The structural parameters of biofilms were studied by using confocal laser scanning microscopy and digital image analysis. The biovolume in the observation field (14,121 μm2 ) of control (untreated) biofilms was 237,333.1 ± 2,692.6 μm3 . The biomass of treated biofilms ranged from 164.7 ± 89.0 μm3 (biofilms exposed to 1010 PFU/mL) to 231,170.5 ± 15,142.0 μm3 (100 PFU/mL). The lowest biomass was achieved after treatment with 108 PFU/mL, with no further decrease in biovolume when higher phage concentrations were used. A strong ( P < 0.001) correlation was found between phage concentration (log units) and biovolume (-0.965), surface coverage (-0.939), roughness (0.976), maximum thickness (-0.853), and average thickness (-0.965). Findings from this research suggest that bacteriophage P100 at concentrations equal to or greater than 8 log PFU/mL successfully removes L. monocytogenes biofilms from polystyrene surfaces.