<i>Corynebacterium striatum</i> modulates the sessile lifestyle of wild-type and Δ <i>srt</i> A mutant <i>Staphylococcus aureus</i> in multi-species biofilms

Corynebacterium striatum and Staphylococcus aureus are opportunistic pathogens that share ecological niches and are frequently co-isolated in healthcare-associated infections. They commonly exist as sessile populations organized within multi-species biofilms associated with medical devices. Sortase A (SrtA) plays a critical role in anchoring surface proteins in S. aureus, thereby influencing adhesion, colonization, and biofilm formation. This study evaluated the influence of C. striatum on the formation and stability of biofilms produced by wild-type and isogenic ΔsrtA mutant S. aureus on hydrophilic and hydrophobic surfaces. Five strains of C. striatum (Cs1–Cs5) and three of S. aureus (Sa1–Sa3) were characterized by biochemical testing, MALDI-TOF MS, antimicrobial susceptibility profiling, and detection of the mecA and srtA genes. The polymeric matrix was assessed on Congo red agar and by staining with Coomassie Brilliant Blue R-250 and safranin. Single- and multi-species biofilms were quantified by colony-forming units at 6, 12, 24, and 48 h, and their architecture was examined using scanning electron microscopy. All strains formed biofilms, including those exhibiting multidrug-resistant phenotypes. In mono-culture, the ΔsrtA mutant of S. aureus displayed reduced adhesion and absence of a detectable polymeric matrix. In co-culture, C. striatum exhibited a progressive competitive advantage, predominating in multi-species biofilms at 48 h. Purified supernatants from C. striatum induced a sessile-to-planktonic transition in S. aureus, reducing adherent populations by up to 5.02 log10, with the ΔsrtA mutant being the most susceptible. These findings suggest that extracellular products derived from C. striatum may contribute to modulation of biofilm stability and sessile behavior, particularly under conditions involving the absence of SrtA-mediated anchoring in S. aureus. The results highlight complex ecological interactions and suggest potential therapeutic strategies based on biofilm interference.