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Infection and Immunity, August 2005, p. 4888-4894, Vol. 73, No. 8
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.8.4888-4894.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Fsr-Independent Production of Protease(s) May Explain the Lack of Attenuation of an Enterococcus faecalis fsr Mutant Versus a gelE-sprE Mutant in Induction of Endocarditis

Kavindra V. Singh,^1,2 Sreedhar R. Nallapareddy,^1,2 Esteban C. Nannini,^1,2, and Barbara E. Murray^1,2,3*

Center for the Study of Emerging and Reemerging Pathogens,¹ Division of Infectious Diseases, Department of Internal Medicine,² Department of Microbiology and Molecular Genetics, The University of Texas Medical School at Houston, Houston, Texas 77030³

Received 17 December 2004/ Returned for modification 26 January 2005/ Accepted 21 March 2005

An Enterococcus faecalis gelE insertion disruption mutant (TX5128), which produces neither gelatinase (GelE) nor the cotranscribed (in the wild type) serine protease (SprE), was found to be attenuated in a rat endocarditis model with a significant decrease in the endocarditis induction rate versus wild-type E. faecalis OG1RF (GelE⁺, SprE⁺). TX5266, which has a nonpolar deletion in fsrB and, like TX5128, is phenotypically GelE^– under usual conditions, was also studied; fsrB is a homologue of agrB of staphylococci and participates in regulation of gelE-sprE expression. Unexpectedly, TX5266 approximated wild-type OG1RF in the endocarditis model and was significantly less attenuated than TX5128. This is in contrast to other models which have found fsr mutants to be as or more attenuated than TX5128. Further study found that the fsrB mutant produced very low levels of gelatinase activity after prolonged incubation in vitro versus no gelatinase activity with TX5128 and did not show the extensive chaining characteristic of TX5128. Reverse transcription-PCR confirmed that gelE was expressed in TX5266 at a very low level versus wild-type OG1RF and was not expressed at all in TX5128. Possible explanations for the increased induction of endocarditis by TX5266 versus TX5128 include the production of low levels of protease(s) or some other effect(s) of the inactivation of the E. faecalis fsr regulator. The equivalent ability of OG1RF and its fsr mutant to initiate endocarditis may explain why we did not find naturally occurring fsr mutants, which account for ca. 35% of E. faecalis isolates, unrepresented in endocarditis versus fecal isolates (J. C. Roberts, K. V. Singh, P. C. Okhuysen, and B. E. Murray, J. Clin. Microbiol. 42:2317-2320, 2004).

Editor: F. C. Fang

Present address: Córdoba 1614, Rosario (2000), Argentina.

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