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DNA banding pattern polymorphism in vancomycin-resistant Enterococcus faecium and criteria for defining strains
D Morrison1, N Woodford, S P Barrett
1Laboratory of Hospital Infection, Central Public Health Laboratory, London, United Kingdom. donald-morrison@msn.com
Abstract:
The degree of DNA banding pattern polymorphism exhibited by vancomycin-resistant Enterococcus faecium (VREM) strains isolated on a renal unit over an 11-month period was investigated. Thirty VREM strains from different patients were analyzed by pulsed-field gel electrophoresis (PFGE; with extended run and optimal pulse times), ribotyping, plasmid profile analysis, biotyping, pyrolysis mass spectrometry, and antibiogram analysis. PFGE resolved 17 banding patterns which formed four distinct clusters at the 82% similarity level. Intercluster band differences ranged from 14 to 31 bands. The strains in one cluster, which contained seven patterns that differed from each other by one to seven bands and from the common pattern by five bands, were confirmed to be a single strain by four of the five other typing methods. The strains in a second cluster with eight patterns, which differed from each other by 1 to 12 bands, contained two subclusters. This subdivision was supported by ribotyping and biotyping. However, it was unclear whether these subclusters represented distinct strains. In one strain, marked polymorphism (patterns that differed from each other by up to four bands) was observed in the ribotype pattern. This study demonstrates the high degree of DNA banding pattern polymorphism found for some strains of VREM and illustrates the complexity involved in defining such strains.
Insights
This study investigated vancomycin-resistant Enterococcus faecium (VREM) DNA banding patterns over 11 months. High DNA polymorphism was observed, highlighting the complexity in defining VREM strains.
Area of Science:
- Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Vancomycin-resistant Enterococcus faecium (VREM) poses a significant threat in healthcare settings, particularly on renal units.
- Understanding the genetic diversity and strain relationships of VREM is crucial for effective infection control.
Purpose of the Study:
- To investigate the DNA banding pattern polymorphism of VREM strains isolated over an 11-month period.
- To assess the discriminatory power of various molecular typing methods for VREM.
Main Methods:
- Thirty VREM strains were analyzed using pulsed-field gel electrophoresis (PFGE), ribotyping, plasmid profiling, biotyping, pyrolysis mass spectrometry, and antibiogram analysis.
- PFGE was optimized with extended run and pulse times to resolve DNA banding patterns.
- Data were analyzed to determine strain similarity and clustering.
Main Results:
- Pulsed-field gel electrophoresis (PFGE) resolved 17 distinct DNA banding patterns, forming four main clusters with 82% similarity.
- Significant intercluster band differences (14–31 bands) were observed.
- One cluster with seven PFGE patterns was confirmed as a single strain by multiple methods, while another cluster showed potential sub-strains.
Conclusions:
- VREM strains exhibit a high degree of DNA banding pattern polymorphism, complicating strain definition.
- Multiple molecular typing methods are necessary to accurately characterize VREM populations.
- The findings underscore the challenges in epidemiological surveillance and control of VREM outbreaks.