Listeria innocua and Listeria monocytogenes strains from dairy plants behave similarly in biofilm sanitizer testing

Five L. innocua and five L. monocytogenes, including persistent and non-persistent isolates collected from Gorgonzola processing plants, were compared regarding their biofilm-forming ability and biofilm susceptibility to two hydrogen peroxide (HP) based disinfectants in use at the plants. No significant difference in biofilm-forming ability by both species was observed (P > 0.05) in crystal violet and viable count assays. The susceptibility to disinfectants was determined in simulated clean and soiled biofilm forming conditions, by growing biofilms, respectively, in 1/10 diluted TSB-YE and in TSB-YE. The results showed no significant differences between species or conditions (P > 0.05) regardless of whether the isolates were classified as persistent or non-persistent. A hierarchical clustering based on Principal Component Analysis performed on the tested variables, indicated the presence of two major clusters. Isolates from both species were allocated in both clusters, suggesting that they behaved in a similar way in response to the tested conditions. This study showed that biofilms of L. innocua could monitor the effectiveness of HP-based disinfectants. Moreover, biofilms of L. innocua from the same environment could be used as surrogates of L. monocytogenes in sanitizer-based biofilm eradication trials simulating dairy processing environments, whenever the use of the pathogen is not an option.