Bacteria colonise surfaces to form biofilms, which are communities that can cause persistent contamination or infections. Understanding the early stages of biofilm formation and the factors that influence it is crucial for developing better prevention strategies. However, capturing the dynamic process of bacterial adhesion and growth on surfaces in real time remains challenging. This study addresses that gap by using a biophysical approach to monitor and characterise surface colonisation by bacteria under various conditions.
Quartz crystal microbalance with dissipation (QCM-D) was used to monitor bacterial adhesion and biofilm formation on gold surfaces in real time. Two model bacteria were studied: Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative). The effects of varying nutrient availability, temperature, and the presence of a quorum sensing inhibitor on biofilm development were examined. Complementary biofilm assays and imaging were performed to confirm and expand upon the QCM-D observations.
QCM-D captured distinct patterns of surface colonisation and biofilm growth, which were
consistent with microscopy and biomass measurements. Both species formed much more extensive biofilms in nutrient-rich broth than in nutrient-poor medium, and a higher temperature (37 °C) accelerated biofilm development compared to room temperature (25 °C). S. aureus and P. aeruginosa exhibited markedly different adhesion behaviours: S. aureus rapidly formed multilayered clusters resulting in a soft, highly viscoelastic biofilm, whereas P. aeruginosa adhered more gradually and produced thinner, stiffer biofilm layers. In S. aureus, inhibiting quorum sensing with savirin delayed biofilm maturation, prolonging the initial attachment phase and reducing overall biofilm accumulation. Comparisons with inert silica colloidal particles indicated that physical deposition alone could mimic the early stage of adhesion, but live bacteria diverged by actively aggregating and producing a viscoelastic polymer matrix.
These findings demonstrate the effectiveness of QCM-D for real-time biofilm monitoring and reveal how growth conditions and microbial traits shape biofilm formation. The study highlights that S. aureus and P. aeruginosa employ different strategies to colonise surfaces, and that interfering with bacterial signalling can modulate biofilm development. Overall, this work provides a more comprehensive biophysical understanding of how biofilms develop on surfaces, which could inform the design of targeted strategies to control or prevent biofilm-related issues
