Effect of sonication on staphylococcal and gram-negative biofilms relevant to prosthetic joint infections: an in vitro study.

backgroundPeriprosthetic joint infections (PJIs) are severe complications of arthroplasty in which biofilm formation on implant surfaces compromises microbiological diagnosis and antimicrobial efficacy. Although staphylococci remain the predominant pathogens, Gram-negative bacilli have increasingly been associated with diagnostic failure and unfavorable clinical outcomes. This study aimed to evaluate the formation, maturation, and structural organization of Gram-positive and Gram-negative bacterial biofilms and to investigate the effects of a standardized sonication protocol on biofilm disruption.

methodsBiofilms of Staphylococcus aureus (ATCC 43300), Staphylococcus epidermidis (ATCC 35984), Escherichia coli (ATCC 25922), and Pseudomonas aeruginosa (ATCC 53278) were formed on polyethylene catheter segments for 24, 48, and 72 h and analyzed by scanning electron microscopy (SEM). A standardized sonication protocol was applied to disrupt the extracellular polymeric substance (EPS) matrix, and the resulting sonication fluid was subsequently cultured. Complementary semi-quantitative image-based analysis was performed to compare structural changes after sonication.

resultsAll species developed progressively mature biofilms over time, with increased structural complexity and EPS accumulation at later stages. Gram-positive bacteria formed denser and more compact biofilms, whereas Gram-negative species exhibited more heterogeneous and multilayered architectures. Sonication consistently disrupted biofilm integrity across all species and maturation stages, leading to fragmentation of the EPS matrix and increased cellular dispersion. Semi-quantitative image-based analysis suggested greater dispersion in Gram-negative biofilms and reduction of biofilm structural area in Gram-positive species, with more pronounced effects observed in P. aeruginosa and S. epidermidis. Bacterial growth was observed in cultures obtained from the sonication fluid after the procedure.

conclusionThe standardized sonication protocol effectively disrupted biofilms formed by both Gram-positive and Gram-negative bacteria, promoting the release of bacterial cells from the biofilm matrix and reinforcing the potential role of sonication as a complementary diagnostic approach for prosthetic joint infections.