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Susceptibility to antimicrobial agents and analysis of plasmids in gentamicin- and methicillin-resistant
Abstract:
Methicillin- and gentamicin-resistant Staphylococcus aureus (MGRSA) strains isolated from Dublin Hospitals were classified into two groups (phenotypes). Phenotype-I strains expressed high level resistance to gentamicin and were susceptible to fusidic acid; strains resistant to tetracycline harboured a 3 X 10(6)-mol. wt plasmid. Strains in phenotype II usually expressed low level resistance to gentamicin, were resistant to fusidic acid and often harboured a (22-24) X 10(6)-mol. wt plasmid that specified resistance to ethidium bromide, tetracycline, kanamycin, neomycin and trimethoprim, or to combinations of these markers. A few phenotype-II strains expressed higher levels of resistance to gentamicin and other aminoglycosides. All MGRSA strains carried a 21 X 10(6)-mol. wt plasmid conferring resistance to penicillin, ethidium bromide, cadmium and mercury. Gentamicin resistance was invariably chromosomal and all strains carried chromosomal resistance to methicillin, erythromycin, streptomycin and spectinomycin. Several methicillin-resistant S. aureus (MRSA) strains isolated before the emergence of gentamicin resistance harboured a 21 X 10(6)-mol. wt penicillinase plasmid with the same restriction endonuclease profile as that from some MGRSA strains. Some MRSA strains carried other plasmids related to those found in MGRSA strains.
Insights
Methicillin- and gentamicin-resistant Staphylococcus aureus (MGRSA) strains exhibit distinct resistance patterns and plasmid profiles. Understanding these differences is crucial for combating hospital-acquired infections.
Area of Science:
- Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant healthcare concern.
- The emergence of gentamicin resistance in MRSA strains (MGRSA) presents new challenges.
- Understanding the genetic basis of MGRSA resistance is vital for effective treatment strategies.
Purpose of the Study:
- To classify MGRSA strains based on their resistance phenotypes and plasmid content.
- To investigate the genetic determinants of methicillin and gentamicin resistance in Staphylococcus aureus.
- To compare plasmid profiles of MGRSA strains with those of earlier MRSA isolates.
Main Methods:
- Phenotypic characterization of MGRSA strains for antibiotic resistance.
- Plasmid profiling using molecular weight determination.
- Analysis of plasmid-borne and chromosomal resistance markers.
- Restriction endonuclease profiling of key plasmids.
Main Results:
- MGRSA strains were classified into two phenotypes based on gentamicin and fusidic acid resistance.
- Phenotype I strains showed high-level gentamicin resistance and carried a 3 x 10(6) mol. wt. plasmid.
- Phenotype II strains typically exhibited low-level gentamicin resistance, fusidic acid resistance, and carried larger plasmids (22-24 x 10(6) mol. wt.) with multiple resistance markers.
- All MGRSA strains possessed a 21 x 10(6) mol. wt. plasmid conferring resistance to penicillin, ethidium bromide, cadmium, and mercury.
- Gentamicin resistance and resistance to methicillin, erythromycin, streptomycin, and spectinomycin were chromosomal.
- Some MRSA strains predating gentamicin resistance shared plasmid profiles with MGRSA strains.
Conclusions:
- MGRSA strains display diverse resistance mechanisms involving both chromosomal and plasmid-borne genes.
- Distinct plasmid types are associated with different MGRSA phenotypes.
- The study highlights the dynamic nature of antibiotic resistance evolution in Staphylococcus aureus.
- Understanding these genetic elements is critical for developing targeted interventions against MGRSA infections.