COMPARISON OF SEROTYPE, BIOTYPE AND BACTERIOCIN TYPE WITH RDNA RFLP PATTERNS FOR THE TYPE IDENTIFICATION OF SERRATIA-MARCESCENS

Variations in rDNA gene loci in DNA digests of 209 clinical isolates o f Serratia marcescens were determined with an Escherichia coli rRNA pr obe. Forty-one restriction fragment length polymorphism patterns (ribo types) were identified, ba.sed on the size of 4-14 (mean 7.5) hybridiz ation bands. The patterns differed by more than a single band in 98 % of pair-wise comparisons. On a subset of 76 isolates, ribotyping prove d to be marginally more discriminating than biotyping (discrimination index 0.92 v. 0.89) followed by serotyping (0.87) and bacteriocin typi ng (0.74). About one-third of isolates belonged to unique ribotypes an d only two ribotypes exceeded 5% in frequency (23.0 and 6-4% respectiv ely). A combination of serotype or biotype with ribotyping defined a s imilar number of strains, although none of the methods alone was suffi ciently discriminatory to identify strains. We conclude that due to th e accessibility of biotyping and the lack of commercially available an tisera for S. marcescens, the biotype and ribotype together provide re liable markers of strain identity.