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Analysis of an outbreak of variably methicillin-resistant Staphylococcus aureus with chromosomal RFLPs and mec region
P R Stewart1, W el-Adhami, B Inglis
1Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra ACT.
Abstract:
An outbreak of infections with multi-resistant Staphylococcus aureus with unusual methicillin resistance at a Melbourne hospital was investigated by examining restriction fragment length polymorphisms (RFLPs) of total DNA digested with the rare-cutting endonuclease SmaI. The polymorphisms were identified by pulsed-field gel electrophoresis (PFGE) and were analysed numerically to give quantitative estimates of genetic distances between isolates. The majority of the isolates were found to belong to one group, with only minor genetic differences between the isolates that showed varying resistance to methicillin, thereby suggesting development of resistant variants from one clonal type during the outbreak. These results were confirmed by DNA hybridisation analysis with specific resistance gene probes for parts of a multi-resistance gene cluster (including methicillin) in the chromosome. Analysis of the RFLP patterns of S. aureus isolates is potentially a useful procedure in clinical epidemiology.
Insights
This study investigated a multi-resistant Staphylococcus aureus outbreak using DNA fingerprinting. Results suggest resistant strains evolved from a single clone, highlighting DNA analysis for tracking hospital infections.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- An outbreak of multi-resistant Staphylococcus aureus with unusual methicillin resistance occurred at a Melbourne hospital.
- Investigating the genetic relatedness of bacterial isolates is crucial for understanding outbreak dynamics.
Purpose of the Study:
- To investigate the genetic relationships between methicillin-resistant Staphylococcus aureus (MRSA) isolates during a hospital outbreak.
- To determine if the outbreak strains originated from a common ancestor.
Main Methods:
- Restriction Fragment Length Polymorphism (RFLP) analysis of bacterial DNA using SmaI endonuclease.
- Pulsed-field gel electrophoresis (PFGE) to separate DNA fragments and identify polymorphisms.
- Numerical analysis of RFLP patterns to estimate genetic distances between isolates.
- DNA hybridization with specific probes to confirm the presence of resistance genes.
Main Results:
- The majority of Staphylococcus aureus isolates belonged to a single genetic group.
- Minor genetic variations were observed among isolates with differing levels of methicillin resistance.
- DNA hybridization confirmed the presence of a multi-resistance gene cluster, including methicillin resistance genes, within the isolates.
- The findings suggest the emergence of resistant variants from a single clonal type during the outbreak.
Conclusions:
- Restriction Fragment Length Polymorphism (RFLP) analysis is a valuable tool for molecular typing of Staphylococcus aureus.
- RFLP patterns can effectively track the evolution and spread of multi-resistant bacteria in clinical settings.
- This method aids in understanding the epidemiology of hospital-acquired infections caused by resistant pathogens.