Standardized method for quantifying colony-forming units in Corynebacterium striatum and Staphylococcus aureus biofilms on hydrophilic and hydrophobic surfaces

The formation of bacterial biofilms on inert surfaces poses a significant challenge in clinical settings, especially concerning medical devices. This study aimed to evaluate the adhesion and biofilm-forming capacity of Corynebacterium and Staphylococcus strains on hydrophilic (glass and polyurethane) and hydrophobic (polystyrene and silicone) surfaces, using a quantitative colony-forming unit (CFU) methodology. Nineteen strains, including clinical isolates and reference strains from a culture collection, were analyzed and identified through phenotypic characterization and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Antimicrobial resistance profiles were determined by the disk-diffusion method, following Clinical and Laboratory Standards Institute (CLSI) guidelines. Biofilm formation was quantified after bacterial growth on each substrate by mechanical disruption using sterilized silica beads, followed by CFU counting. Hydrophilic surfaces, particularly glass and polyurethane, promoted significantly greater bacterial adhesion. Among the strains tested, S. aureus (Sa-191-0033169) and C. striatum (Cs-319-0001961) exhibited the highest adhesion and biofilm production. The CFU-based quantification technique proved highly sensitive in detecting viable cells within biofilms, outperforming traditional methods such as crystal violet staining and metabolic assays like XTT. These findings highlight the importance of considering both the physicochemical properties of materials and the genetic background of bacterial strains when developing strategies to prevent and control biofilm-associated nosocomial infections on medical devices.