Nosocomial transmission of Serratia odorifera biogroup. 2: Case report demonstration by macrorestriction analysis of chromosomal DNA using pulsed-field gel electrophoresis.

Objectives: To investigate a cluster of Serratia odorifera in a cardiothoracic surgery unit (CTSU) and to evaluate the applicability of three typing methods for this species. Design: During a surveillance surgical wound study, S odorifera was isolated from two patients in the CTSU. The patients' hospital charts were reviewed for the details of surgery and for common personnel, procedures, or medications. Cultures were obtained of water, soap, and unit dose medications from the CTSU, the operating room, and the surgical intensive care unit. The isolates' antibiograms, biotypes (Vitek identification card and API 20E), and patterns of chromosomal DNA (chrDNA) by pulsed-field gel electrophoresis (PFGE) were examined. S odorifera isolates from our organism collection were used as controls. Setting: A 900-bed university hospital with a 22-bed CISU. Results: ChrDNA patterns of isolates from the two patients were identical, suggesting a possible nosocomial source. However, no source of organisms or mode of transmission was identified. Neither biotype nor antibiogram were useful for epidemiologically typing S odorifera , and PFGE was necessary to discriminate among isolates. Conclusions: Although rarely isolated, S odorifera and other non- marcescens Serratia species may cause nosocomial outbreaks. PFGE of chrDNA seems to be a reliable method for epidemiologically typing this species.