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Journal of Clinical Microbiology, September 2009, p. 2802-2811, Vol. 47, No. 9
0095-1137/09/$08.00+0     doi:10.1128/JCM.00485-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of Clinical Enterococcus faecalis Small-Colony Variants{triangledown}

Nele Wellinghausen,1* Indranil Chatterjee,2 Anja Berger,3 Andrea Niederfuehr,1 Richard A. Proctor,4 and Barbara C. Kahl5

Institute of Medical Microbiology and Hygiene, University Hospital of Ulm, Ulm,1 Institute of Medical Microbiology and Hygiene, Institutes of Infectious Disease Medicine, University of Saarland, Homburg/Saar,2 Bavarian Health and Food Safety Authority, Oberschleissheim,3 Institute of Medical Microbiology, University Hospital of Muenster, Muenster, Germany,5 Departments of Medicine and Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, Wisconsin4

Received 9 March 2009/ Returned for modification 17 June 2009/ Accepted 7 July 2009

In this report, we present a clinical case of chronic aortic valve endocarditis caused by Enterococcus faecalis small-colony variants (SCVs), with ensuing characterization of the SCV phenotype in comparison to the clonally related normal phenotype with respect to alterations in microscopic and ultrastructural morphology, growth behavior, and metabolic pathways. In contrast to the normal phenotype, light and electron microscopy of the Enterococcus SCVs demonstrated the presence of heterogeneous cells of different sizes with aberrant shapes. Furthermore, SCVs showed excessive production of an intercellular substance and alterations in cell division displayed by a thick, coarse cell wall and incomplete, branched, and multiple cross walls without obvious cell separation. In addition, empty "ghost" cells were visible. In growth experiments, SCVs displayed an extended lag phase with delayed entrance into the stationary phase. Interestingly, SCV cells growing under aerobic conditions did not attain the growth and viability of the normal phenotype or those of SCVs growing under microaerobic conditions, suggesting impaired growth behavior and enhanced vulnerability in the presence of oxygen. By metabolite analysis, SCVs failed to produce significant amounts of acetate or lactate under aerobic growth conditions but were able to produce lactate under microaerobic growth conditions, implicating the induction of a fermentative metabolism. In conclusion, the observed structural alterations and changes in the cellular growth and metabolic pathways facilitated the survival of Enterococcus SCVs under microaerobic conditions in vitro and thus presumably in vivo during endocarditis.

* Corresponding author. Current address: Dr. Gaertner & Colleagues Laboratories, Elisabethenstr. 11, D-88212 Ravensburg, Germany. Phone: 49-751-502 220. Fax: 49-751-502 833. E-mail: nele.wellinghausen{at}labor-gaertner.de

{triangledown} Published ahead of print on 15 July 2009.

Journal of Clinical Microbiology, September 2009, p. 2802-2811, Vol. 47, No. 9
0095-1137/09/$08.00+0     doi:10.1128/JCM.00485-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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