Molecular surveillance of clinical methicillin-resistant Staphylococcus aureus isolates in neonatal intensive care units

BACKGROUND AND OBJECTIVE: Methicillin-resistant Staphylococcus aureus (MRSA) has become an important nosocomial pathogen in our neonatal intensive care units (NICUs) and accounts for almost all S. aureus clinical isolates. The objective of this study was to assess the relatedness of these MRSA strains. DESIGN: MRSA clinical isolates were collected from infants hospitalized in our NICUs. Pulsed-field gel electrophoresis with SmaI digestion was used to fingerprint these isolates. SETTING: Level-III NICUs in a university-affiliated children's hospital. RESULTS: Between 1998 and 2000, a total of 122 MRSA clinical isolates were collected from 104 infants hospitalized in our NICUs. Fifteen infants had multiple isolates (range, 2 to 4 isolates). The sources of specimens included blood (72), pus (23), sputum (15), body fluids (3), and catheter tips (9). A total of 4 genotypes with 20 subtypes were identified. There were 2 genotypes in 1998, 2 genotypes in 1999, and 4 genotypes in 2000. All but 2 isolates belonged to either genotype A (63.1%; 7 subtypes) or genotype C (35.2%; 11 subtypes). Among the 15 infants with multiple isolates, the genotypes of the isolates from a single episode of MRSA infection were different in 2 of 12 cases, and reinfection with a new strain was noted in 3 of 5 cases with recurrent infections. CONCLUSIONS: Two predominant MRSA clones prevailed in our NICUs between 1998 and 2000. Polyclonal bacteremia and reinfection with a new strain were noted.