A formal analysis of Listeria monocytogenes cross-contamination dynamics in multi-species biofilms.

Food contamination by Listeria monocytogenes usually occurs in food processing environments, where bacteria coexist in multi-species biofilms. Using a stochastic modelling approach, this study addressed the cross-contamination dynamics of cold-smoked salmon by L. monocytogenes from multi-species biofilms (3) formed by bacterial consortia from food industry surfaces under conditions reproducing low L. monocytogenes loads. Single-species biofilms were also formed for comparison. Transfer rates (TR) were determined over successive contacts of each biofilm with 25 salmon slices. Modelling of TR probabilities revealed distinct contamination profiles. Differences were particularly marked between multi- and single-species biofilms, likely indicating the influence of the coexisting microbiota. Subsequently, the growth of L. monocytogenes in cold-smoked salmon after transfer from multi-species and single-species biofilms was examined. L. monocytogenes from multi-species biofilms showed higher growth than single-species biofilms, which would markedly increase food safety risk. These findings are critical for designing realistic challenge studies and improving contamination control of ready-to-eat foods.