APPLICATION OF A BIOTYPING SYSTEM AND DNA RESTRICTION FRAGMENT ANALYSIS TO THE STUDY OF SERRATIA-MARCESCENS FROM HOSPITALIZED-PATIENTS

We applied a nine-test biotyping system to the study of 138 Serratia marcescens isolates from 93 patients hospitalized in 33 different hospital bed units. Test reproducibility for a panel of 10 isolates tested in triplicate on 3 separate days was 100%. Overall, the biotyping system delineated 25 strains. In examining strain variation among isolates obtained from multiple anatomic sites over time we found that the same biotype was recovered from tracheal aspirates, urine, wounds, and blood in a given patient and that these strains were carried over time. In general, patients were infected or colonized with their own distinct biotype of S. marcescens. Temporally related isolates from seven surgical intensive care unit (SICU) patients and six unrelated control isolates were typed by biotyping and DNA restriction fragment analysis (RFA). The distribution of biotypes was similar among SICU outbreak and control isolates, with five distinct biotypes among the seven SICU isolates. Each isolate had a different DNA subtype by RFA, confirming the lack of nosocomial transmission of a single strain. These results will be useful in studying the epidemiology of S. marcescens.