Tissue destruction during food spoilage is associated with the formation of biofilms by Pseudomonas species

Members of the Pseudomonas genus are common spoilers of a range of meat, dairy and vegetable products. While we have a good understanding of the Pseudomonas species typically responsible for spoilage, we know very little about how these bacteria interact with food surfaces during spoilage. Here we assessed the spoilage capabilities of a large panel (n = 124) of Pseudomonas species food-derived isolates on meat (chicken) and leafy greens (spinach). Most isolates (71/124) were capable of spoiling both foods, but some were only capable of spoiling only chicken (21/124) or spinach (23/124), or neither (9/124). Our data also demonstrated that the type of fresh food the strain was isolated from influenced spoilage capabilities: strains isolated from meat products were equally likely to spoil both chicken and spinach; isolates from seafood products were significantly more likely to spoil chicken; and those isolated from leafy greens were significantly more likely to spoil spinach. We used fluorescence microscopy to visualise how Pseudomonas spoilage species interacted with the meat or leaf tissue and observed significant tissue destruction associated with biofilm formation. For chicken, this was associated with the formation of dense biofilm pillars that penetrated deep into the tissue. For spinach we observed biofilms on the leaf in areas of tissue degradation. Finally, we explored the correlation between potentially relevant phenotypes (in vitro biofilm, motility and secreted enzyme production) and spoilage capabilities. After controlling for the phylogenetic relationships between samples there was no evidence for association between these phenotypes and spoilage capability in either product. Overall, this study increases our understanding of processes involved in food spoilage by Pseudomonas species.