Characterizing interactions of Staphylococcus aureus and Escherichia coli in dual-species implant-associated biofilms

While Staphylococcus aureus is the predominant pathogen in periprosthetic joint infections (PJI), polymicrobial infections involving Gram-negative organisms, such as Escherichia coli, complicate clinical outcomes. Little is known regarding implant-associated polymicrobial interactions; consequently, current PJI treatments are not optimized for their treatment. This study explored the dynamics of S. aureus-E. coli dual-species biofilms, focusing on biofilm properties, antibiotic susceptibility, and molecular interactions. Co-culture experiments revealed that E. coli significantly suppressed S. aureus biofilm viability, observed for methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Microscopic analyses demonstrated enhanced E. coli attachment facilitated by S. aureus matrix proteins; however, over time, E. coli dominated the biofilm composition. In the presence of E. coli, MSSA biofilm exhibited improved gentamicin susceptibility while MRSA showed limited change, underscoring strain-specific interactions. Notably, E. coli biofilms exhibited enhanced resistance to gentamicin in dual-species settings. Gene expression profiling revealed molecular adaptation in S. aureus and E. coli, triggered by the differential regulation of stress, adhesion, virulence, and biofilm-associated genes within a dual-species implant-associated biofilm. The suppression of S. aureus by E. coli presents potential therapeutic avenues, and in vivo studies and mechanistic investigations are crucial for optimizing treatment strategies targeting polymicrobial PJIs.