Related Experiment Videos
Distribution of plasmid-borne resistance to nucleic acid binding compounds in methicillin-resistant Staphylococcus
Abstract:
Methicillin-resistant Staphylococcus aureus (MRSA) which are epidemic in Australian hospitals have been found to be genetically different from strains previously isolated in Australia and in Europe. A characteristic feature of the recent Australian isolates is a plasmid which encodes resistance to nucleic acid binding compounds (NAB) such as propamidine isethionate. Of 753 MRSA strains isolated from around the world in 1980-1983, c. 60% were NAB resistant. The determinant for this resistance could be transferred from 90% of strains to a recipient strain in mixed culture. A plasmid analysis revealed that, in general, the largest plasmid of MRSA isolates coded for NAB resistance and may carry other determinants for penicillinase production and resistance to gentamicin, trimethoprim, neomycin, tetracycline, cadmium and mercury. Some plasmids exhibited unusual behaviour with the appearance of deletion mutants after transfer and, in one case, a high-frequency alteration in the expression of gentamicin resistance from high-level to low-level resistance, correlated to a deletion of c. 0.5 megadalton of plasmid DNA. These results demonstrate that these NAB-resistance plasmids are not unique to Australian MRSA strains but are widely distributed throughout the world.
Insights
New Methicillin-resistant Staphylococcus aureus (MRSA) strains in Australian hospitals carry plasmids conferring resistance to nucleic acid binding compounds (NAB). These NAB-resistance plasmids are widespread globally in MRSA, not unique to Australia.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in hospital settings worldwide.
- Recent MRSA isolates in Australian hospitals exhibit genetic differences compared to historical and European strains.
- A key distinguishing feature of these Australian strains is the presence of plasmids encoding resistance to nucleic acid binding compounds (NAB).
Purpose of the Study:
- To investigate the prevalence and characteristics of NAB resistance plasmids in global MRSA isolates.
- To determine if NAB resistance plasmids found in Australian MRSA are unique or widespread.
- To analyze the genetic features and transferability of these resistance determinants.
Main Methods:
- Analysis of 753 MRSA strains isolated globally between 1980-1983.
- Plasmid DNA analysis and characterization.
- Bacterial conjugation experiments to assess plasmid transferability.
- Investigation of plasmid deletion mutants and their effect on antibiotic resistance expression.
Main Results:
- Approximately 60% of the global MRSA strains analyzed were resistant to NAB compounds.
- The NAB resistance determinant was transferable via mixed culture in 90% of resistant strains.
- The largest plasmid in MRSA isolates generally conferred NAB resistance and potentially other resistance traits (e.g., gentamicin, tetracycline).
- Plasmid transfer sometimes resulted in deletion mutants, including alterations in gentamicin resistance expression linked to DNA deletions.
Conclusions:
- NAB resistance plasmids are not unique to Australian MRSA strains but are widely distributed internationally.
- These plasmids are mobile genetic elements that can carry multiple resistance genes.
- Plasmid instability, including deletions, can influence the expression of antibiotic resistance phenotypes.