PHENOTYPIC VARIATION OF CLINICAL SERRATIA-MARCESCENS ISOLATES REPEATEDLY RECOVERED FROM INDIVIDUAL PATIENTS

A total of 129 selected isolates of Serratia marcescens which had been recovered from 50 patients during the 1980-1995 period and which reve aled phenotypic variation in terms of bacteriocin (phage tail) suscept ibility, carbon source assimilation, or serotype, were reexamined with these three phenotypic methods. Seven isolates (5.4%) were bacterioci n nontypable; all 129 isolates utilized carbon sources and could be se rotyped. Fourty-eight isolates from 20 patients yielded unambiguous re sults with these 3 phenotypic methods and were excluded from further a nalysis. Among the remaining 81 isolates from 30 patients, isolates fr om 2 patients revealed phenotypic variation in bacteriocin susceptibil ity only, whereas isolates from 6 patients showed variant bacteriocin types and variant biochemical profiles, but were of identical serotype . Isolates from 20 patients revealed variant biochemical profiles only . Three patients had become superinfected with strains of S. marcescen s of different phenotype and genotype. In 4 patients, previously motil e (H12) isolates had become nonmotile (H-). PFGE analysis of XbaI and SpeI-restricted genomic DNA of the 81 isolates of the 30 patients demo nstrated the isolates of 22 patients to be genotypically identical. Th e isolates from 3 patients were closely related by genotype, and those from an additional patient proved to be possibly related. PFGE analys is demonstrated one patient to have become infected by two genotypical ly different strains of S. marcescens of identical serotype, which, ho wever, differed in bacteriocin type and biochemical profile. It was co ncluded that PFGE analysis of restricted genomic S. marcescens DNA was superior to the three phenotypic methods examined comparatively. Sero typing was more reliable than bacteriocin typing, and the latter techn ique yielded fewer phenotypic variants than determination of biochemic al profiles among consecutively recovered isolates from patients with long-lasting S. marcescens infection.