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Journal of Clinical Microbiology, February 2003, p. 867-872, Vol. 41, No. 2
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.2.867-872.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Comparative Analysis of Multidrug-Resistant, Non-Multidrug-Resistant, and Archaic Methicillin-Resistant Staphylococcus aureus Isolates from Central Sydney, Australia

Department of Infectious Diseases and Immunology, University of Sydney,¹ Department of Microbiology, Royal Prince Alfred Hospital, Sydney,³ Department of Public Health, Adelaide,² Department of Microbiology and Infectious Diseases, Concord Repatriation General Hospital, Concord, Australia⁴

Received 2 October 2001/ Returned for modification 18 December 2001/ Accepted 14 November 2002

In this study, the phenotypic and genotypic characteristics of 50 methicillin-resistant Staphylococcus aureus (MRSA) isolates (43 contemporary and 7 archaic strains from the mid-1960s) from four Sydney hospitals in the central Sydney area were compared. Phenotypic analysis based on antibiotic profiles and phage typing patterns categorized the MRSA isolates into three major groups: multidrug resistant (mMRSA), non-multidrug resistant (nmMRSA), and archaic. The nmMRSA isolates could be further subdivided into nmMRSA group 1, which was phage typeable and similar to the archaic group; nmMRSA group 2, which was non-phage typeable and only resistant to ciprofloxacin; and nmMRSA group 3, which was also nontypeable and generally resistant to other antibiotics. The characterization of all five phenotypic groups was then extended by genetic analysis. Restriction fragment length polymorphism (RFLP) analysis showed the 50 isolates could be sorted into 20 group-specific pulsotypes. mecI gene deletions and mutations at various percentages among the five MRSA groups were detected by sequencing. Several mec promoter mutations were also found. The overall findings indicated that nmMRSA strains may have independently acquired mec DNA and are more likely to be newly emergent strains than nmMRSA variants.