Antimicrobial Susceptibility Patterns and Biofilm Formation of Staphylococcus aureus Strains Isolated from Pediatric Patients with Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction and susceptibility to Staphylococcus aureus colonization. Biofilm formation modifies antibiotic resistance and the host immune response. This longitudinal study analyzed antimicrobial susceptibility and biofilm formation in 136 S. aureus isolates obtained over 18 months from lesional, nonlesional, and nasal samples of 26 pediatric patients with moderate-to-severe AD. Antimicrobial susceptibility testing was determined by the disk diffusion method, and biofilm production was quantified using a crystal violet microtiter assay. Clinical parameters, including disease severity, treatment response, and the administration of dilute bleach baths, were evaluated in relation to bacterial characteristics. Overall, 60.2% of isolates exhibited moderate-to-strong biofilm production, significantly associated with severe AD at baseline (p = 0.01), lack of clinical improvement (p = 0.04), and persistent moderate-to-severe disease (p = 0.01). Resistance rates for penicillin, gentamicin, clindamycin, and erythromycin exceeded 15%. Isolates from patients using dilute bleach baths showed greater resistance to ciprofloxacin (p < 0.0001) and exhibited constitutive or inducible macrolide–lincosamide–streptogramin B (MLSB) resistance, with ermA detected in 80% of inducible cases. In conclusion, S. aureus biofilm formation is linked to disease severity and treatment failure in pediatric AD, underscoring the importance of culture-guided, targeted therapeutic strategies.