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Epidemiological validation of pulsed-field gel electrophoresis patterns for methicillin-resistant Staphylococcus
D S Blanc1, M J Struelens, A Deplano
1Division Autonome de Médecine Préventive Hospitalière, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. Dominique.Blanc@chuv.hospvd.ch
Abstract:
To determine the stability of pulsed-field gel electrophoresis (PFGE) patterns of methicillin-resistant Staphylococcus aureus in the nosocomial setting, we analyzed isolates from long-term carriers (>1 month) and from patients involved in well-defined nosocomial epidemics. The number of fragment differences between the first isolate and subsequent isolates in long-term carriers showed a bimodal distribution, with one group having 0 to 6 fragment differences and the other group having 14 to 24 fragment differences. The PFGE patterns of isolates involved in epidemics also presented a similar bimodal distribution of the number of fragment differences. Typing these isolates with another molecular method (inter-IS256 PCR) showed that isolates of the first group (i.e., with 1 to 6 fragment differences) were clonally related, whereas the second group (with 14 to 24 fragment differences) could be considered genetically different. Among long-term carriers with clonally related isolates, 74 of 84 (88%) of consecutive isolates showed indistinguishable patterns, whereas 10 of 84 (12%) showed related patterns differing by one to six fragments. Moreover, the frequency of apparition of related patterns is higher when the time between the first and the subsequent isolate is longer. During seven nosocomial epidemics lasting from 1 to 15 months, only 2 of 120 isolates (1.7%) showed a pattern which was different, although related, from the predominant one involved in each of these outbreaks.
Insights
Pulsed-field gel electrophoresis (PFGE) patterns of methicillin-resistant Staphylococcus aureus are generally stable in hospitals. Most long-term carriers and epidemic isolates showed minimal or no changes in PFGE patterns over time.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of nosocomial infections.
- Understanding the genetic stability of MRSA strains is crucial for infection control and outbreak investigations.
Purpose of the Study:
- To assess the stability of pulsed-field gel electrophoresis (PFGE) patterns of MRSA in a hospital setting.
- To differentiate between clonally related and genetically distinct MRSA isolates over time and during outbreaks.
Main Methods:
- Analysis of MRSA isolates from long-term carriers (>1 month) and nosocomial epidemics using PFGE.
- Comparison of fragment differences between sequential isolates.
- Confirmation of clonal relatedness using inter-IS256 PCR.
Main Results:
- PFGE patterns showed a bimodal distribution of fragment differences (0-6 vs. 14-24) in both carriers and epidemic isolates.
- Isolates with 1-6 fragment differences were clonally related, while those with 14-24 were genetically distinct.
- In long-term carriers, 88% of consecutive isolates had indistinguishable PFGE patterns; 12% showed related patterns (1-6 fragment differences).
- During seven epidemics, only 1.7% of isolates showed a related, but different, pattern from the predominant outbreak strain.
Conclusions:
- MRSA PFGE patterns exhibit considerable stability in the nosocomial environment, particularly for clonally related isolates.
- Minor genetic variations (1-6 fragments) can occur over time, especially in long-term carriers.
- PFGE is a reliable tool for tracking MRSA strains during hospital-acquired infections and outbreaks.