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Evolution of Australian isolates of methicillin-resistant Staphylococcus aureus: a problem of plasmid
Abstract:
Methicillin-resistant Staphylococcus aureus (MRSA), currently causing problems in Australian hospitals, have chromosomal penicillinase and carry a new family of incompatibility group I (IncI) plasmids that encode resistance to nucleic acid-binding compounds (NAB). These plasmids may carry additional determinants for penicillinase production and resistance to gentamicin and trimethoprim. By comparison, earlier MRSA isolates from Australia were NAB-sensitive and the penicillinase determinants were carried on IncI plasmids. The possibility that these newer MRSA isolates have the same 'clonal' origin as other MRSA isolates has been investigated. Forcible maintenance of IncI penicillinase plasmids and NAC-resistance plasmids in the same cells resulted in various recombination events. Similar recombination events to those generated in the laboratory have been found in MRSA isolates.
Insights
Newer Australian Methicillin-resistant Staphylococcus aureus (MRSA) strains carry novel IncI plasmids conferring resistance to nucleic acid-binding compounds (NAB). Laboratory studies revealed recombination events similar to those found in clinical MRSA isolates.
Area of Science:
- Microbiology
- Genetics
- Hospital Epidemiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant challenge in Australian hospitals.
- Previous Australian MRSA isolates were sensitive to nucleic acid-binding compounds (NAB) and carried penicillinase determinants on IncI plasmids.
- Emerging MRSA strains exhibit altered resistance profiles, necessitating investigation into their genetic origins and plasmid content.
Purpose of the Study:
- To investigate the genetic relatedness of newer Australian MRSA isolates to earlier ones.
- To characterize the IncI plasmids and their associated resistance determinants in contemporary MRSA strains.
- To explore potential recombination events contributing to MRSA evolution.
Main Methods:
- Plasmid analysis of MRSA isolates.
- Investigation of resistance determinants, including those for penicillinase, gentamicin, and trimethoprim.
- Laboratory-based experiments involving forced maintenance of IncI penicillinase and NAB-resistance plasmids in bacterial cells.
- Comparative analysis of laboratory-generated recombination events with those observed in clinical isolates.
Main Results:
- Newer Australian MRSA isolates carry IncI plasmids encoding resistance to NAB.
- These plasmids may also confer resistance to gentamicin and trimethoprim.
- Laboratory-induced recombination between IncI penicillinase plasmids and NAB-resistance plasmids generated events mirroring those found in clinical MRSA isolates.
Conclusions:
- The findings suggest a potential common clonal origin for different MRSA isolates, linked by plasmid dynamics.
- Recombination events involving IncI plasmids play a role in the evolution and spread of antibiotic resistance in MRSA.
- Understanding these genetic mechanisms is crucial for controlling MRSA in healthcare settings.