Corynebacterium striatum modulates the population dynamics of wild-type and ΔagrA mutant Staphylococcus aureus in multi-species biofilms

Corynebacterium striatum and Staphylococcus aureus are opportunistic pathogens frequently isolated from nosocomial infections, but their interactions within multi-species biofilms remain poorly understood. This study evaluated the influence of C. striatum on biofilm formation by wild-type and Δ agr A S. aureus . Clinical and reference strains were characterized phenotypically (biochemical tests, slime production on Congo Red agar) and genotypically (MALDI-TOF MS, detection of mec A and agr locus genes, construction of a Δ agr A isogenic mutant). The single- and multi-species biofilms were quantified on hydrophilic and hydrophobic surfaces over 48 h, and their architecture and extracellular polymeric substances (EPS) were analyzed through differential staining and field emission scanning electron microscopy (FESEM). The effect of C. striatum cell-free supernatants (CFS) on the dispersal of S. aureus biofilms was also assessed. Both species formed robust single-species biofilms, with variability among strains. In multi-species biofilms, synergistic interactions were observed, increasing total biomass, with C. striatum often predominating, particularly on glass surfaces. Exposure to CFS reduced sessile cells and increased planktonic populations, suggesting active dispersal, with Δ agr A being more susceptible, underscoring the role of the agr system. Therefore, C. striatum influences the sessile lifestyle of S. aureus , possibly via quorum sensing (QS), acting as an ecological modulator in multi-species biofilms, with implications for anti-biofilm strategies.