Antimicrobial susceptibility patterns of and biofilm formation by Staphylococcus aureus strains isolated from pediatric patients with atopic dermatitis

Background: Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction and susceptibility to Staphylococcus aureus colonization. Biofilm formation alters antibiotic resistance and the immune response. This study examines the antimicrobial susceptibility patterns and biofilm formation of S. aureus isolates from pediatric AD patients. Methods: A prospective longitudinal observational study was conducted with 136 S. aureus isolates collected from 26 pediatric patients with moderate-to-severe AD over 18 months. Isolates were obtained from both lesional and nonlesional skin and from nares. Antimicrobial susceptibility was evaluated using the disk diffusion method, whereas biofilm production was quantified using a crystal violet microtiter assay. Clinical characteristics, including AD severity, response to treatment, and the use of adjunctive dilute bleach baths, were analyzed for associations with S. aureus features. Results: Of the isolates, 60.2% exhibited moderate-to-strong biofilm production, which was associated with severe AD at baseline (p=0.01), lack of clinical improvement (p=0.04), and persistent moderate-severe disease (p=0.01). The antimicrobial resistance rates for penicillin, gentamicin, clindamycin, and erythromycin exceeded 15%. Isolates from patients receiving dilute bleach baths presented greater resistance to ciprofloxacin (p<0.0001) and constitutive and inducible macrolide-lincosamide-streptogramin B resistance (MLSB). Inducible MLSB was associated with the ermA gene in 80% of the cases. Conclusions: S. aureus biofilm formation correlates with disease severity and treatment resistance in pediatric AD patients. These findings highlight the need for culture-guided therapy and emphasize the importance of tailored strategies to manage S. aureus colonization and infection in AD patients.