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Phenotypic variation of clinical Serratia marcescens isolates repeatedly recovered from individual patients
W H Traub1, A Eiden, B Leonhard
1Institut für Medizinische Mikrobiologie und Hygiene, Universität des Saarlandes, Homburg/Saar, Germany.
Abstract:
A total of 129 selected isolates of Serratia marcescens which had been recovered from 50 patients during the 1980-1995 period and which revealed phenotypic variation in terms of bacteriocin (phage tail) susceptibility, carbon source assimilation, or serotype, were reexamined with these three phenotypic methods. Seven isolates (5.4%) were bacteriocin nontypable; all 129 isolates utilized carbon sources and could be serotyped. Fourty-eight isolates from 20 patients yielded unambiguous results with these 3 phenotypic methods and were excluded from further analysis. Among the remaining 81 isolates from 30 patients, isolates from 2 patients revealed phenotypic variation in bacteriocin susceptibility 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. marcescens of different phenotype and genotype. In 4 patients, previously motile (H12) isolates had become nonmotile (H-). PFGE analysis of XbaI and SpeI-restricted genomic DNA of the 81 isolates of the 30 patients demonstrated the isolates of 22 patients to be genotypically identical. The isolates from 3 patients were closely related by genotype, and those from an additional patient proved to be possibly related. PFGE analysis demonstrated one patient to have become infected by two genotypically different strains of S. marcescens of identical serotype, which, however, differed in bacteriocin type and biochemical profile. It was concluded that PFGE analysis of restricted genomic S. marcescens DNA was superior to the three phenotypic methods examined comparatively. Serotyping was more reliable than bacteriocin typing, and the latter technique yielded fewer phenotypic variants than determination of biochemical profiles among consecutively recovered isolates from patients with long-lasting S. marcescens infection.
Insights
Pulsed-field gel electrophoresis (PFGE) is superior for tracking Serratia marcescens infections compared to phenotypic methods. PFGE accurately identifies genotypic variations in bacterial strains during long-term patient infections.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Serratia marcescens infections can exhibit phenotypic variation over time.
- Traditional methods like bacteriocin susceptibility, carbon source assimilation, and serotyping have limitations in accurately characterizing strain diversity.
- Long-term infections present challenges in distinguishing between strain evolution and new infections.
Purpose of the Study:
- To compare the discriminatory power of Pulsed-field gel electrophoresis (PFGE) with traditional phenotypic methods for analyzing Serratia marcescens isolates.
- To investigate genotypic and phenotypic diversity of S. marcescens in patients with prolonged infections.
- To determine the most reliable method for tracking S. marcescens strain evolution and superinfections.
Main Methods:
- Phenotypic characterization of 129 Serratia marcescens isolates from 50 patients using bacteriocin susceptibility, carbon source assimilation, and serotyping.
- Genomic DNA analysis of 81 selected isolates from 30 patients using PFGE with XbaI and SpeI restriction enzymes.
- Comparative analysis of results obtained from phenotypic methods and PFGE.
Main Results:
- PFGE analysis demonstrated genotypic identity in isolates from 22 patients, close relatedness in 3, and possible relatedness in 1.
- Phenotypic methods revealed variations in bacteriocin susceptibility, biochemical profiles, and serotypes, but were less discriminatory than PFGE.
- One patient was infected with two genotypically distinct S. marcescens strains exhibiting identical serotypes but different bacteriocin types and biochemical profiles.
- PFGE identified genotypic variations missed by phenotypic methods, including superinfections and strain evolution.
Conclusions:
- PFGE is a superior method for analyzing genotypic relatedness of Serratia marcescens isolates compared to phenotypic methods.
- Serotyping is more reliable than bacteriocin typing, which is less reliable than biochemical profiling for detecting phenotypic variants.
- PFGE is crucial for accurately identifying distinct strains and understanding the dynamics of S. marcescens infections in patients.