Molecular epidemiology of coagulase-negative staphylococci causing sepsis in a neonatal intensive care unit over an 11-year period

Coagulase-negative staphylococci (CoNS) are the major causative microorganisms in neonatal nosocomial sepsis. Previous studies have shown that CoNS sepsis in the neonatal intensive care unit (NICU) is caused by predominant molecular types that are widely distributed among both neonates and staff. Some of these molecular types may persist in the NICU for years. The purpose of the present study was to determine the dynamic behavior of CoNS strains causing sepsis over a prolonged period of time by determining the molecular types of all blood isolates from septicemic infants over a period of 11 years (1991 to 2001). The results show that neonatal CoNS sepsis is increasingly caused by a few predominant molecular clusters. The most striking finding was that in recent years one molecular cluster emerged as the predominant cause of neonatal CoNS sepsis, responsible for no less than 31% (20 of 65) of blood isolates in 2001. Antibiotic resistance, particularly beta-lactam resistance, is probably an important selective force considering the high mecA gene carriage of CoNS blood isolates (70 to 92%). We conclude that neonatal CoNS sepsis is increasingly caused by a limited number of predominant molecular CoNS types and that antibiotic resistance is probably a major selective force.