Dynamics of multi-species biofilm formation on food contact surfaces

Food packaging is an essential component of the food industry as it protects and conserves foods and products. However, food contact surfaces are prone to microbial adhesion and biofilm formation, which, in turn, contribute to food contamination and increase the risk of foodborne illness. The most common foodborne pathogens are Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, and Pseudomonas aeruginosa, which are able to form single- or multi-species biofilms. The formation of multi-species biofilms is particularly problematic, as they are often more resistant to disinfection procedures. Hence, it is important to understand the dynamics of multi-species biofilm formation on polymeric surfaces typically used for food packaging (e.g. polylactic acid (PLA) and silicone) in order to develop effective strategies to prevent biofouling.

For this purpose, biofilm assays were conducted in 12-well microtiter plates using S. aureus (SH1000 expressing GFP) and P. aeruginosa (PO1 expressing mCherry). Single- and dual-species biofilms were formed on PLA and polydimethylsiloxane (PDMS) surfaces for 72 h at 4 °C without shaking to simulate food packaging conditions. The number of total cells was determined by flow cytometry based on GFP and mCherry expression, while the number of culturable cells was estimated by counting colony-forming units (CFU) using selective culture media.

Results showed that there were no significant differences between the number of total and culturable cells of S. aureus and P. aeruginosa biofilms formed on PDMS and PLA surfaces. S. aureus displayed lower biofilm-forming capability compared to P. aeruginosa (p < 0.001). Dual-species biofilms contained more cells than those formed by S. aureus or P. aeruginosa (p = 0.001). In addition, dual-species biofilms were almost entirely composed of P. aeruginosa (90%) and presented a higher number of cells on PDMS than on PLA surface (p = 0.003).

Altogether, these results suggest that, in dual-species biofilms, there is probably an interaction of commensalism between P. aeruginosa and S. aureus, with benefits for the former. In addition, both polymeric surfaces are susceptible to microbial adhesion and biofilm formation, which can compromise food quality and safety.