Detection, isolation and characterisation of Listeria monocytogenes-carrying biofilms from surfaces of meat, seafood and dairies processing plants

A survey to detect and characterise biofilms carrying Listeria monocytogenes from different industries belonging to fish, meat and cheese processing facilities was carried out. A total of 328 samples, including processing lines and related environments, from 3 seafood industries (n=181), 15 meat-processing plants (n=75) and from 4 cheese industries (n=72) were checked. 16S rDNA-based identification and RAPD-typing of each positive sample were further carried out so as to characterise the microbial communities’ composition of L. monocytogenes-carrying biofilms isolated from the different sectors. Eventually, the most representative dual-species association of L. monocytogenes were selected to assess their compatibility when forming mixed biofilms in a stainless steel model surface system at 25ºC. Twelve different mono and multiple-species Listeria-carrying communities were eventually isolated. Whereas the incidences of L. monocytogenes in seafood and meat processing industries were 3 and 8% respectively, no confirmed positive samples for L. monocytogenes were detected in cheese industries. RAPD-typing of L. monocytogenes isolates obtained rendered 6 different types with a homogeneous distribution in the some of the plants, especially in those of seafood. Subsequent identifications of accompanying bacteria (n=27) belonging to 17 different species highlight L. monocytogenes-Escherichia coli (37.5%) and L. monocytogenes-Carnobacterium spp. (36.3%) as the most abundant co-presence in fish and meat-manufacturing premises respectively. Finally, compatibility experiments showed that only when L. monocytogenes was cultured in presence Serratia sp. or Pseudomonas sp., a significant decrease (α<0.05) in the adhered L. monocytogenes biomass in stainless steel coupons was detected after 48 hours, indicating that most of the identified dual-species biofilms (9 out of 11) could be easily present in real food environments when both individual species are nearly located in the space. Obtained results contribute to elucidate bacterial interactions in natural environments and also to deepen in the ecology of L. monocytogenes biofilms in food processing plants in order to improve industrial hygiene and safeness to avoid final cross-contamination of food, leading to food spoilage and loss of economic benefits or even food-borne outbreaks.