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Antibiotic resistances and plasmids in Staphylococcus aureus from Italian hospitals
Abstract:
A total of 473 Staphylococcus aureus isolates from six Italian hospitals was examined for susceptibility to several antimicrobial agents and for plasmid content. Methicillin-resistant S. aureus (MRSA) were characterised by a plasmid of mol. wt (10(6)) 18-22 or 25 that carried the determinants for penicillinase production, resistance to cadmium ions and resistance to tetracycline. MRSA isolates usually harboured other smaller plasmids of mol. wt (10(6)) 2.8, 2.6 and 1.65 that encoded resistance to tetracycline, chloramphenicol and erythromycin, respectively, and cryptic plasmids of mol. wt (10(6)) c. 2 and 1 were found frequently. Methicillin-sensitive S. aureus (MSSA) that produced penicillinase often carried plasmids of mol. wt (10(6)) 11 or 13. No particular difference was found in plasmid patterns of strains from the various sources. Analysis of plasmids by EcoRI digestion showed that plasmids of similar mol. wt and phenotypic characteristics may have different restriction patterns, but often share one or more fragments in common.
Insights
This study analyzed 473 Staphylococcus aureus isolates, identifying specific plasmids in methicillin-resistant S. aureus (MRSA) linked to antibiotic resistance. Plasmid profiles varied, but common resistance determinants were observed in these hospital-acquired bacterial strains.
Area of Science:
- Microbiology
- Molecular Biology
- Medical Science
Background:
- Staphylococcus aureus is a significant human pathogen, with antibiotic resistance posing a major public health challenge.
- Methicillin-resistant S. aureus (MRSA) strains are a particular concern due to their resistance to a wide range of antibiotics.
- Plasmids are extrachromosomal DNA elements that often carry genes conferring antibiotic resistance, playing a crucial role in bacterial adaptation and spread.
Purpose of the Study:
- To investigate the plasmid content of Staphylococcus aureus isolates from Italian hospitals.
- To correlate plasmid profiles with antimicrobial susceptibility patterns, particularly in MRSA.
- To characterize the genetic determinants of resistance carried on plasmids in S. aureus.
Main Methods:
- Phenotypic characterization of 473 S. aureus isolates for antimicrobial susceptibility.
- Plasmid DNA extraction and analysis of molecular weight (mol. wt).
- Restriction enzyme digestion (EcoRI) of plasmids to analyze their genetic structure.
Main Results:
- MRSA isolates were characterized by plasmids (mol. wt 18-22 or 25 x 10^6) encoding penicillinase production, cadmium, and tetracycline resistance.
- Smaller plasmids (mol. wt 2.8, 2.6, 1.65 x 10^6) in MRSA carried resistance to tetracycline, chloramphenicol, and erythromycin, respectively.
- Methicillin-sensitive S. aureus (MSSA) producing penicillinase often carried plasmids (mol. wt 11 or 13 x 10^6); plasmid patterns showed no significant variation across hospitals.
Conclusions:
- Specific plasmids are associated with key resistance mechanisms in S. aureus, including MRSA.
- The presence of multiple resistance-conferring plasmids contributes to the multidrug-resistant phenotype of S. aureus.
- Plasmid analysis, including restriction digestion, provides insights into the genetic diversity and relatedness of S. aureus strains.