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Antimicrob. Agents Chemother. doi:10.1128/AAC.01099-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Reconstruction of the phenotypes of methicillin resistant Staphylococcus aureus (MRSA) by replacement of the staphylococcal cassette chromosome mec (SCCmec) with a plasmid-borne copy of S. sciuri pbpD gene

Laboratory of Microbiology, The Rockefeller University, New York, NY 10021, USA

^* To whom correspondence should be addressed. Email: tomasz{at}rockefeller.edu.

	Abstract

The mecA gene, the central determinant of methicillin resistant Staphylococcus aureus (MRSA), is not native to this bacterial species but may have originated in the animal commensal species Staphylococcus sciuri. All S. sciuri strains carry a close homologue of mecA in the form of pbpD, the genetic determinant of penicillin binding protein (PBP) 4 of S. sciuri. Here we describe an experimental system that could provide additional tests for this proposition. The S. sciuri pbpD gene was cloned into a shuttle plasmid and introduced into a methicillin susceptible S. aureus strain COL-S derived from the parental MRSA strain COL from which the resistance cassette SCCmec was excised. The S. sciuri pbpD determinant was transcribed and translated in the S. aureus transductants producing large amounts of the 84 kDa S. sciuri PBP4 which was deposited in the plasma membrane of the host bacterium. Transductants carrying the heterologous S. sciuri pbpD gene exhibited typical properties of the parental MRSA strain COL including broad spectrum, high level, and homogeneous resistance to structurally different -lactams. Antibiotic resistance was dependent on the functioning of S. aureus PBP2 and was suppressed by the specific regulatory genes mecI/mecR and by inhibitors of an early step in cell wall biosynthesis. S. sciuri PBP4 was also able to replace the essential physiological function(s) of the native PBP2 of S. aureus and produce peptidoglycan typical of the parental MRSA strain COL. Our results provide further support that the resistance determinant mecA of MRSA strains has evolved from S. sciuri pbpD.