Evaluation the effect of CeO₂ nanoparticles on the expression of biofilm-associated genes in Staphylococcus aureus isolated from wound infections

Staphylococcus aureus (S. aureus) is one of the most dangerous human pathogens, and its capacity to form biofilms is linked to the persistence of infection and increased resistance to antimicrobial agents. The aim of this study was to assess the effect of cerium dioxide nanoparticles (CeO₂ NPs) on biofilm formation and the gene expression of the icaA and icaD genes in S. aureus isolates. Fifty-six isolates were collected from wound infections in several hospitals in Baghdad and identified using the VITEK-II system and 16S rRNA PCR,. Antibiotic susceptibility testing revealed a high prevalence of methicillin-resistant Staphylococcus aureus (MRSA), at 85.71%. All isolates demonstrated the ability to form biofilms; 58.93% were moderate producers, 17.86% were strong producers, and 23.21% were weak producers. The icaA and icaD genes were also found in all 30 isolates selected for molecular analysis (100%).The CeO₂ nanoparticles were characterized using XRD, FT-IR, AFM and SEM. The minimum inhibitory concentration (MIC) was 12,500 μg/mL for all isolates. Sub-MIC treatment effectively inhibited biofilm formation, showing the strongest effect on high-production isolates (95.42%), followed by medium- (89.28%) and low-production isolates (88.36%). CeO₂ nanoparticles also demonstrated a clear and statistically significant reduction in gene expression; the mean change in expression was 0.091 for the icaA gene and 0.077 for the icaD gene compared with the control group. The nanoparticles also exhibited antioxidant activity, achieving an inhibition rate of 59.2% ± 1.05 at the lowest concentration used (0.003 μg/ml)