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Journal of Clinical Microbiology, June 2003, p. 2444-2447, Vol. 41, No. 6
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.6.2444-2447.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Infection of a Ventriculoatrial Shunt with Phenotypically Variable Staphylococcus epidermidis Masquerading as Polymicrobial Bacteremia Due to Various Coagulase-Negative Staphylococci and Kocuria varians

Infectious Diseases Unit,¹ Division of Epidemiology,² Microbiology Laboratory, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel³

Received 25 September 2002/ Accepted 24 February 2003

The diagnosis of bloodstream infection with coagulase-negative staphylococci is frequently based on the isolation of the same organism from more than one blood culture. Phenotypic variation is a common characteristic of pathogenic strains of Staphylococcus epidermidis which may affect species identification by the microbiology laboratory. We describe a patient with a new onset of nephritis and gram-positive bacteremia. Gram-positive cocci grew in multiple blood cultures and were identified by the Vitek 2 system as Kocuria varians, Staphylococcus hyicus, and S. epidermidis. Bacterial isolates grew on blood agar and Congo red agar plates as two distinct morphotypes and exhibited phenotypic variation. Neither morphotype could be identified by the API-Staph assay. Cellular fatty acid analysis identified one of the morphotypes as S. epidermidis but could not identify the other morphotype. All isolates were found to be identical by pulsed-field gel electrophoresis, and both colonial morphotypes were identified as S. epidermidis by 16S ribosomal gene sequencing. Phenotypic variation of S. epidermidis may affect identification to the species level by phenotype-based identification systems. Caution should be exercised when differentiating between true infection and contamination based on strain identification.

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• Ben-Ami, R., Navon-Venezia, S., Schwartz, D., Schlezinger, Y., Mekuzas, Y., Carmeli, Y. (2005). Erroneous Reporting of Coagulase-Negative Staphylococci as Kocuria spp. by the Vitek 2 System. J. Clin. Microbiol. 43: 1448-1450 [Abstract] [Full Text]