To our knowledge, no studies have previously been carried out on the heterogeneity and intrafamily colonization of impetigo Staphylococcus aureus strains obtained by powerful discriminating methods such as pulsed-field gel electrophoresis (PFGE). To explore this topic, macrorestriction patterns of S. aureus strains were analyzed after SmaI and SgrAI digestion. The two enzymes provided superimposable results. A total of ninety-seven S. aureus strains was found in the 26 families whose lesions and nasal and pharyngeal samples were examined. There were 39 strains which were different by PFGE, and of these, 24 were found in the lesions. Although 85% of impetigo patients showed nasal colonization and 58% showed pharyngeal colonization, only 54% of the patients had the same PFGE strain in the lesion and in the nose, and 35% in the lesion and the pharynx. In half of the 26 families, at least one member (mother, father, or relative) presented a S. aureus strain identical, by PFGE, to strains isolated in patients' lesions. Nineteen percent of mothers, 15% of fathers, and 19% of the other relatives presented nasal colonization with strains identical to those isolated in the children's lesions. Lesional strains showed higher antimicrobial resistance than nonlesional isolates. (C) 2000 Editions scientifiques et medicales Elsevier SAS.