Comparative evaluation of an automated repetitive-sequence-based PCR instrument versus pulsed-field gel electrophoresis in the setting of a Serratia marcescens nosocomial infection outbreak

A semiautomated repetitive-sequence-based polymerase chain reaction (rep-PCR) instrument (DiversiLab system) was evaluated in comparison with pulsed-field gel electrophoresis (PFGE) to investigate an outbreak of Serratia marcescens infections in a neonatal intensive care unit (NICU). A selection of 36 epidemiologically related and eight epidemiologically unrelated isolates were analyzed. Among the epidemiologically related isolates PFGE identified five genetically unrelated patterns. Thirty-two isolates from patients and wet nurses showed an identical PFGE profile (pattern A). Genetically unrelated PFGE patterns were found in one patient (pattern B), in two wet nurses (patterns C,D), and in the NICU environmental isolate (pattern G). Rep-PCR identified seven different patterns, three of which included the 32 isolates belonging to PFGE type A. One to two band differences in isolates belonging to these three types allowed isolates to be categorized as similar and included in a unique cluster. Isolates belonging to different PFGE types also exhibited unrelated rep-PCR types. All the epidemiologically unrelated isolates belonged to different PFGE and rep-PCR types. The level of discrimination exhibited by rep-PCR with the DiversiLab system allowed to conclude that this method was able to identify genetic similarity in a spatio-temporal cluster of Serratia marcescens isolates.