Bacteriocin typing and biotyping of clinical isolates of Serratia marcescens

A total of 727 clinical isolates of Serratia marcescens from 474 patients were typed for bacteriocin susceptibility; 707 of the isolates (97.25%) were typable and comprised 46 different bacteriocin types. The biotyping method of Grimont and Grimont permitted categorization of 726 of the 727 isolates into 50 biotype profiles. However, 98 of the 726 biotypable isolates (13.5%) yielded previously unknown biotype profiles; similarly, 24 out of 59 reference strains of S. marcescens gave biotype profiles that had not been encountered before. Multiple S. marcescens isolates (366 of the 727 isolates) had been recovered from 113 patients. Phenotypic variation in bacteriocin susceptibility occurred in 15 of these patients, whereas phenotypic variation in biotype profiles was noted in 26 of these patients. In 5 of the 113 patients, phenotypic variation accounted for changes both in bacteriocin type and in biotype profile. It is suggested that serotyping should remain the method of choice until new methods have been evaluated accordingly.