Virulence and Antibiotic Resistance Profiles of Staphylococcus aureus Isolated from Epidermal Growth Factor Receptor Inhibitors-Associated Skin Lesions.

Cutaneous adverse reactions (CARs) are common complications of epidermal growth factor receptor (EGFR) inhibitor therapy, with papulopustular eruptions and paronychia being the most frequent. Growing scientific evidence implies that Staphylococcus aureus is involved in the pathogenesis of these reactions. This observational prospective study characterized 42 S. aureus strains isolated from CARs, analyzing antibiotic resistance, biofilm formation, soluble virulence factors, and virulence/resistance genes using multiplex polymerase chain reaction (PCR). S. aureus was identified in 90% of lesions; in 33% of cases, nasal and skin isolates were genetically identical. High resistance rates were noted for penicillins (85%) and tetracyclines (57%), while all strains remained susceptible to fluoroquinolones, vancomycin, and rifampicin. All isolates formed biofilms, and DNase/esculinase production significantly correlated with CAR severity. An enzymatic score based on these markers was associated with an 18-fold increased risk of severe reactions. Genotypically, clfA and clfB were prevalent (85.7%), while exotoxin genes were less common. These findings support a key role for S. aureus in exacerbating CARs via antibiotic resistance, biofilm production, and the expression of virulence factor. Additionally, we emphasize the role of routine microbial screening-including nasal swabs-and therapy guided by antibiograms. Furthermore, the enzymatic score may further be validated as a predictive biomarker.