Detection of Listeria monocytogenes in Biofilms Using Immunonanoparticles

In this study, a nanoparticle-based immunoassay was developed for the sensitive detection of Listeria monocytogenes in biofilms. L. monocytogenes Scott A labeled with green fluorescent protein (GFP) was grown on glass slide to form a mono-species biofilm, or co-cultured with Pseudomonas aeruginosa ATCC 27853 to form a two-species biofilm. The anti-L. monocytogenes-coated nano-particles specifically recognized L. monocytogenes in monospecies biofilms However, under the same confocal laser scanning microscopy conditions, anti-L. monocytogenes-nanoparticles generated higher intensity of fluorescent signals, which ranged from 0 to 4000, than anti-L. monocytogenes alone did, which was in the range of 0 to 250. In two-species biofilms, L. monocytogenes cells at different depths (0–5 μm) of biofilms were successfully detected by both nanoparticle-based indirect immunoassay and fluorescent nanoparticle-based direct immunoassay but not traditional immunoassay. The results demonstrate that these nanoparticle-based immunoassays were more sensitive than traditional immunoassays for detecting L. monocytogenes in mono- or two-species biofilms.