USE OF PULSED-FIELD GEL-ELECTROPHORESIS TYPING TO STUDY AN OUTBREAK OF INFECTION DUE TO SERRATIA-MARCESCENS IN A NEONATAL INTENSIVE-CARE UNIT

Serratia marcescens is a well-known cause of nosocomial infections and outbreaks, particularly in critically ill neonates and immunocompromi sed patients. Numerous methods have been proposed for typing. We used pulsed-held gel electrophoresis (PFGE) typing to analyze an outbreak i n a neonatal intensive care unit (NICU). We included 23 patient isolat es from an outbreak (March to July 1995), and 10 patient isolates from different wards during the same time period. PFGE of whole-cell DNA d igested by SpeI was used as a marker of strain identity. The most comm on presentation of the infection was sepsis in 18 of 23 (78%) neonates . Only four different biotypes were identified; biotype A8d accounted for 84% of the strains. PFGE typing revealed two clones responsible fo r two different clonal strain dissemination outbreaks from March to Ju ly, with 24 patient isolates being pattern A and 4 patient isolates be ing pattern E. PFGE typing suggests cross transmission between patient s in the NICU and other wards. The isolates from 5 other patients show ed distinct PFGE patterns. Extensive investigation and cultures failed to identify any environmental or staff reservoir of S. marcescens. Th is is one of the first reports applying PFGE to the study of S. marces cens, and this method was a useful marker of strain identity. PFGE typ ing distinguished strains which appeared to be the same by biotyping.