Typing of nosocomial Strains of Serratia marcescens: Comparison of restriction enzyme cleaved genomic DNA fragment (PFGE) analysis with bacteriocin typing, biochemical profiles and serotyping

Eighty-eight selected clincial isolates of Serratia marcescens, representing 27 putative outbreaks of nosocornial cross-infection encountered during 1980–1995, were tested comparatively by bacteriocin typing, carbon source assimilation tests, serotyping (0 and H antigens), and restriction pattern (RFLP) analysis of restriction cleaved (Spel, XbaI) genomic DNA fragments after pulsed-field gel electrophoresis (PFGE). Serotyping served as the “gold standard” of the phenotypic methods. One pseudo-outbreak (bacteriocin typing incriminated type 26) was uncovered through serotyping as well as the biochemical profile and confirmed by PFGE analysis of genomic DNA. Bacteriocin typing and determination of biochemical profiles disclosed several instances of phenotypic variation; serotyping revealed two episodes of shifts from motility (H12) to nonmotility. Resolution of restricted genomic DNA fragments with the PFGE procedure permitted detection of 27 PFGE patterns (A-M, N-1-N-3, O-1, O-2, P-1-P-3, Q-1-Q-3, R-1-R-3, S-1, and T). Based on the analysis of PFGE patterns against the background of epidemiological data, the number of nosocomically significant strains of S. marcescens could be reduced to 16 (PFGE patterns A-M, N-2, O-1, P-2, and T). It was concluded that PFGE analysis of restricted genomic DNA of S. marcescens was superior to the three phenotypic methods.