Characteristics and distribution of plasmids in a clonally diverse set of methicillin-resistant Staphylococcus aureus strains
The aim of this study was to compare the plasmid contents of methicillin-resistant Staphylococcus aureus (MRSA) strains classified into different clonal clusters (CCs). The isolates were collected from 15 Czech hospitals in 2000–2008. Plasmid DNA was detected in 65 (89%) strains, and 33 of them harbored more than one plasmid type. Altogether 24 different types of plasmids were identified, ranging in size from 1.3 to 55 kb. Restriction endonuclease analysis, plasmid elimination, DNA hybridization, and sequencing were used for their further characterization. It has been found that the conjugative, erythromycin resistance and enterotoxin D encoding plasmids are harbored by strains from different CCs. On the other hand, chloramphenicol and tetracycline resistance plasmids, and most of the penicillinase and cryptic plasmids were only detected in certain CCs. Especially, the pUSA300-like plasmids were found exclusively in the USA300 clone strains. The high diversity in plasmid content detected in the study strains implies that plasmids play a major role in evolution of MRSA clonal lineages.
KeywordsMethicillin-resistant Staphylococcus aureus Plasmids Genetic diversity Antibiotic resistance Molecular typing
We would like to thank M. Kolářová, A. Ševčíková, and M. Hanslianová from the University Hospital Brno for collecting MRSA isolates and Eva Kodytková for valuable help. We gratefully acknowledge the financial support of the European Union (grant LSHM-CT-2006-019064) (StaphDynamics), Czech Science Foundation (310/09/0459), and Ministry of Education, Youth and Sports of the Czech Republic (MSM 0021622415).
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