Assessment of the effect of culture components of clinical Pseudomonas aeruginosa isolates on vancomycin eradication of Staphylococcus aureus mature biofilms

BACKGROUND: P. aeruginosa and S. aureus are frequently co-isolated from chronic biofilm-associated infections. Microbial interactions within biofilms affect antimicrobial susceptibility, making treatment more challenging. This study aimed to investigate the effect of P. aeruginosa superinfection on mature S. aureus biofilm eradication by vancomycin. METHODS: Biofilm-producing clinical isolates of S. aureus and MDR P. aeruginosa were collected from chronic wound infections. Baseline viable cell counts in 24-hour S. aureus biofilms were determined. The minimal biofilm eradication concentration (MBEC) of vancomycin was assessed in the presence and absence of P. aeruginosa culture components. Relative gene expression of ldh and adh in biofilm cells was evaluated by RT-qPCR. RESULTS: Superinfection with P. aeruginosa reduced the viable counts of S. aureus biofilm cells and altered vancomycin MBEC for planktonic-phase biofilm cells. Disruption of S. aureus biofilms by MDR P. aeruginosa culture supernatants reduced ldh and adh gene expression, with an effect comparable to, but not additive with, that of vancomycin. CONCLUSION: Vancomycin eradication of S. aureus planktonic biofilm cells is altered by MDR P. aeruginosa superinfection. Both vancomycin and MDR P. aeruginosa culture supernatants, individually and combined, interfered with the anaerobic respiration pathways in sessile biofilm cells.