{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,20]],"date-time":"2026-02-20T05:08:33Z","timestamp":1771564113330,"version":"3.50.1"},"reference-count":33,"publisher":"Proceedings of the National Academy of Sciences","issue":"17","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2001,8,14]]},"abstract":"<jats:p>\n            The key genetic component of methicillin resistance, the\n            <jats:italic>mecA<\/jats:italic>\n            determinant, is not native to\n            <jats:italic>Staphylococcus\n aureus<\/jats:italic>\n            . Thus, the evolution of methicillin-resistant\n            <jats:italic>S.\n aureus<\/jats:italic>\n            (MRSA) must have begun with the acquisition of the\n            <jats:italic>mecA<\/jats:italic>\n            determinant from an unknown heterologous source\n some time before the first reported appearance of MRSA isolates in\n clinical specimens in the U.K. and Denmark (in the early 1960s). We\n compared the genetic backgrounds and phenotypes of a group of\n methicillin-susceptible\n            <jats:italic>S. aureus<\/jats:italic>\n            (MSSA) isolates to the\n properties of MRSA strains isolated in Denmark and the U.K. during the\n same time period, and also to the genetic profiles of contemporary\n epidemic clones of MRSA. All early MRSA isolates resembled a large\n group of the early MSSA blood isolates in phenotypic and genetic\n properties, including phage group, antibiotype (resistance to\n penicillin, streptomycin, and tetracycline), pulsed-field gel\n electrophoresis pattern, and\n            <jats:italic>spaA<\/jats:italic>\n            type and multilocus\n sequence type, strongly suggesting that the early MSSA examined here\n represented the progeny of a strain that served as one of the first\n            <jats:italic>S. aureus<\/jats:italic>\n            recipients of the methicillin-resistance\n determinant in Europe. The genetic background of this group of early\n MSSA isolates was also very similar to that of the widely disseminated\n contemporary \u201cIberian clone\u201d of MRSA, suggesting that genetic\n determinants present in early MSSA and essential for some aspects of\n the epidemicity and\/or virulence of these strains may have been\n retained by this highly successful contemporary MRSA lineage.\n          <\/jats:p>","DOI":"10.1073\/pnas.161272898","type":"journal-article","created":{"date-parts":[[2002,7,26]],"date-time":"2002-07-26T14:37:36Z","timestamp":1027694256000},"page":"9865-9870","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":223,"title":["The evolution of methicillin resistance in\n            <i>Staphylococcus aureus<\/i>\n            : Similarity of genetic backgrounds in historically early methicillin-susceptible and -resistant isolates and contemporary epidemic clones"],"prefix":"10.1073","volume":"98","author":[{"given":"M. In\u00eas","family":"Cris\u00f3stomo","sequence":"first","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, NY 10021; Department\r of Clinical Microbiology, Hvidovre Hospital, DK-2650 Hvidovre,\r Denmark; and Staphylococcus Laboratory, Statens Serum\r Institute, DK-2300 Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Henrik","family":"Westh","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, NY 10021; Department\r of Clinical Microbiology, Hvidovre Hospital, DK-2650 Hvidovre,\r Denmark; and Staphylococcus Laboratory, Statens Serum\r Institute, DK-2300 Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexander","family":"Tomasz","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, NY 10021; Department\r of Clinical Microbiology, Hvidovre Hospital, DK-2650 Hvidovre,\r Denmark; and Staphylococcus Laboratory, Statens Serum\r Institute, DK-2300 Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Marilyn","family":"Chung","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, NY 10021; Department\r of Clinical Microbiology, Hvidovre Hospital, DK-2650 Hvidovre,\r Denmark; and Staphylococcus Laboratory, Statens Serum\r Institute, DK-2300 Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Duarte C.","family":"Oliveira","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, NY 10021; Department\r of Clinical Microbiology, Hvidovre Hospital, DK-2650 Hvidovre,\r Denmark; and Staphylococcus Laboratory, Statens Serum\r Institute, DK-2300 Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Herm\u00ednia","family":"de Lencastre","sequence":"additional","affiliation":[{"name":"Laboratory of Molecular Genetics, Instituto de Tecnologia\r Qu\u00edmica e Biol\u00f3gica, Universidade Nova de Lisboa, 2780\r Oeiras, Portugal; Laboratory of Microbiology, The\r Rockefeller University, New York, 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