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 <i>Staphylococcus aureus</i> colonization. Biofilm formation modifies antibiotic resistance and the host immune response. This longitudinal study analyzed antimicrobial susceptibility and biofilm formation in 136 <i>S. aureus</i> 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 (<i>p</i> = 0.01), lack of clinical improvement (<i>p</i> = 0.04), and persistent moderate-to-severe disease (<i>p</i> = 0.01). Resistance rates for penicillin, gentamicin, clindamycin, and erythromycin exceeded 15%. Isolates from patients using dilute bleach baths showed greater resistance to ciprofloxacin (<i>p</i> < 0.0001) and exhibited constitutive or inducible macrolide-lincosamide-streptogramin B (MLS_B) resistance, with <i>erm</i>A detected in 80% of inducible cases. In conclusion, <i>S. aureus</i> biofilm formation is linked to disease severity and treatment failure in pediatric AD, underscoring the importance of culture-guided, targeted therapeutic strategies.