Inhibition of multispecies biofilm formation by Listeria monocytogenes, Salmonella spp., and associated microbiota using thymol, carvacrol, lactic and acetic acid, and silver and zinc oxide nanoparticles

This study evaluated the dynamics of biofilm formation in pure and multispecies cultures of Listeria monocytogenes, Salmonella spp., and associated microbiota on polypropylene surfaces, as well as the inhibitory effects of thymol and carvacrol (THY + CAR), silver and zinc oxide nanoparticles (AgNPs + ZnONPs), and lactic and acetic acids (LA + AA) on multispecies biofilm development. Analyses included viable cell counts, microbial diversity profiling, and characterization of biofilm structure. The formation dynamics of pure and multispecies biofilms exhibited specific differences depending on incubation time; however, all biofilms reached similar cell densities after 216 h. THY + CAR exhibited the highest inhibitory effect (reductions of 99.77 %–99.9998 %), followed by LA + AA (39.34 %–99.993 %) and AgNPs + ZnONPs (57.08 %–97.01 %). These treatments also inhibited the growth of L. monocytogenes (83.89 %–99.9995 %) and Salmonella spp. (91.36 %–99.9998 %). Microbial community analysis revealed that the Yersiniaceae family was consistently present under all conditions. Moraxellaceae was more abundant in untreated biofilms, whereas Pseudomonadaceae dominated treated biofilms. Scanning electron microscopy revealed that all compounds inhibited biofilm development by reducing cell density and extracellular polymeric substances. These findings suggest that the tested compounds may serve as effective adjuncts to cleaning and sanitization protocols in the food industry.