Can Staphylococcus aureus form biofilm on uncoated plastic?

Introduction: Plastics provide physical support to microorganisms for biofilm formation (BF), protecting them from extreme conditions and facilitating their persistence for extended periods. While previous studies have focused on the impact of (plasma‐)treated plastic surfaces with improved hydrophilicity on the ability of bacteria to form biofilm, little is known about the influence of pristine (micro)plastics with strong hydrophobic properties in the attachment of foodborne pathogens. Purpose: In this study, we analysed the ability of bacteria to form biofilm on uncoated plastic at different temperatures using Staphylococcus aureus as model organism, one of the most common causes of foodborne intoxication worldwide. Methods: The ability of 35 S. aureus strains isolated from food and clinical samples to form biofilm was determined on flat-bottomed, non-treated 96-well polystyrene microtiter plates for 24 h at 22°C and 37°C following the crystal violet staining method. Moreover, the isolates were sequenced using the Nanopore technology to analyze their genetic content and identify potential genes associated with their biofilm-forming ability through a Genome-Wide Association Study using Scoary. Results: BF was found to be dependent on the strains (p < 0.001) and the temperature (p < 0.001), with increasing BF at 37°C (0.161 ± 0.089) compared to 22°C (0.114 ± 0.031). A total of 21 S. aureus strains (60%) were able to form biofilm at any temperature, although only 10 (28.6%) formed biofilm at both temperatures. Moreover, the sasG gene was the only biofilm-associated gene that was found to be significantly associated with BF (Fisher’s exact p = 0.007). However, when the pangenome was investigated, no gene showed a statistically significant association with BF (p > 0.05). Significance: The ability of S. aureus to form biofilm on pristine plastic pose a significant challenge to food safety and public health by facilitating the persistence of the pathogen in the environment.