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Persistence of a clone of methicillin-resistant Staphylococcus aureus in a burns unit
A M Al-Haddad, E E Udo1, E M Mokadas1
1School of Biomedical Sciences, Curtin University of Technology, Perth, Western Australia and *Department of Microbiology, Faculty of Medicine, Kuwait University, PO Box 24923, Safat 13110, Kuwait.
Abstract:
A total of 128 MRSA isolates from a burns unit in 1992 and 1997 was studied by resistotyping, plasmid analysis and pulsed-field gel electrophoresis (PFGE) of SmaI-digested chromosomal DNA to ascertain whether a clone of MRSA had persisted in the unit or whether different clones had been introduced at different times. All the MRSA isolates produced beta-lactamase and had high MICs to methicillin (>256 mg/L). All were resistant to tetracycline, kanamycin, cadmium acetate and mercuric chloride. Most were resistant to gentamicin, neomycin, erythromycin, chloramphenicol, trimethoprim, ciprofloxacin, propamidine isethionate and ethidium bromide, and were susceptible to minocycline, vancomycin and teicoplanin. None of the 1992 isolates was resistant to mupirocin, but 56% and 19% of the 1997 isolates expressed high- and low-level mupirocin resistance, respectively. Many of the 1997 isolates had acquired a 38-kb plasmid encoding high-level mupirocin resistance. The 1992 isolates had two main PFGE patterns; 82% of them belonged to PFGE pattern 1. The 1997 isolates had PFGE pattern 1, the same as the majority of the 1992 isolates. All MRSA isolates from both years carried the mecA gene in the same SmaI fragment. These findings demonstrated that a clone of MRSA that was prevalentin the burns unit in 1992 had persisted and became the predominant clone in 1997.
Insights
A persistent Methicillin-resistant Staphylococcus aureus (MRSA) clone dominated a burns unit from 1992 to 1997. This MRSA clone acquired mupirocin resistance, indicating evolving antimicrobial resistance patterns in healthcare settings.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in healthcare settings, particularly in specialized units like burn centers.
- Understanding the clonal dynamics and resistance mechanisms of MRSA is crucial for effective infection control and treatment strategies.
Purpose of the Study:
- To investigate the persistence and evolution of MRSA clones within a burns unit over a five-year period (1992-1997).
- To determine if a specific MRSA clone remained prevalent or if new clones were introduced.
- To analyze the acquisition of antimicrobial resistance, including mupirocin resistance, within the MRSA population.
Main Methods:
- Resistotyping, plasmid analysis, and pulsed-field gel electrophoresis (PFGE) of SmaI-digested chromosomal DNA were employed.
- 128 MRSA isolates collected in 1992 and 1997 from a burns unit were analyzed.
- Antimicrobial susceptibility testing was performed for various agents, including methicillin, mupirocin, and heavy metals.
Main Results:
- A predominant MRSA clone identified in 1992 persisted and remained the dominant clone in 1997.
- A significant increase in mupirocin resistance was observed in 1997 isolates, with many acquiring a 38-kb plasmid encoding this resistance.
- All analyzed MRSA isolates carried the mecA gene within the same SmaI chromosomal fragment.
Conclusions:
- The study demonstrates the persistence of a specific MRSA clone in a burns unit over five years.
- The emergence and spread of mupirocin resistance within this persistent clone highlight evolving resistance challenges.
- These findings underscore the importance of continuous surveillance and molecular typing for MRSA in healthcare environments.