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Infection and Immunity, December 1998, p. 5988-5993, Vol. 66, No. 12
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Selective Activation of sar Promoters with the Use of Green Fluorescent Protein Transcriptional Fusions as the Detection System in the Rabbit Endocarditis Model

A. L. Cheung,1,* Cynthia C. Nast,2,3 and A. S. Bayer3,4

Laboratory of Bacterial Pathogenesis and Immunology, The Rockefeller University, New York, New York 100211; Department of Pathology, Cedars-Sinai Medical Center, Los Angeles, California 900482; and St. John's Cardiovascular Research Center and Division of Infectious Diseases, Harbor-UCLA Medical Center,4 and UCLA School of Medicine,3 Los Angeles, California 90024

Received 22 June 1998/Returned for modification 23 July 1998/Accepted 13 August 1998

The global regulatory locus sar is composed of three overlapping transcripts initiated from a triple-promoter system (designated P1, P3, and P2). To explore if the individual sar promoters are differentially expressed in vitro and in vivo, we constructed a shuttle plasmid (pALC1434) containing a promoterless gfpUV gene (a gfp derivative [Clontech]) preceded by a polylinker region. Recombinant shuttle vectors containing individual sar promoters upstream of the gfpUV reporter gene were then introduced into Staphylococcus aureus RN6390. Northern and immunoblot analysis revealed that P1 is stronger than the P2 and P3 promoters in vitro. Additionally, the levels of the gfpUV transcript driven by individual sar promoters also correlated with the growth cycle dependency of these promoters in liquid cultures, thus suggesting the utility of pALC1434 as a vehicle for reporter fusion. Using the rabbit endocarditis model, we examined the expression of these three GFPUV fusions in vivo by fluorescence microscopy of infected cardiac vegetations 24 h after initial intravenous challenge. Similar to the in vitro findings, P1 was activated both in the center and on the surface of the vegetations. In contrast, the P3 promoter was silent both in vivo and in vitro as determined by fluorescence microscopy. Remarkably, P2 was silent in vitro but became highly activated in vivo. In particular, the sar P2 promoter was activated on the surface of the vegetation but not in the center of the lesion. These data imply that in vivo promoter activation of sar differed from that observed in vitro. Moreover, the individual sar promoters may be differentially expressed in different areas within the same anatomic niche, presumably reflecting the microbial physiological response to distinct host microenvironments. As the sar locus controls the synthesis of both extracellular and cell wall virulence determinants, these promoter-gfpUV constructs should be useful to characterize many aspects of S. aureus gene regulation in vivo.

* Corresponding author. Mailing address: The Laboratory of Bacterial Pathogenesis and Immunology, The Rockefeller University, 1230 York Ave., New York, NY 10021. Phone: (212) 327-8163. Fax: (212) 327-7584. E-mail: cheunga{at}Rockvax.rockefeller.edu.

Infection and Immunity, December 1998, p. 5988-5993, Vol. 66, No. 12
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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