Identification of Enterococcus species using an automated microarray-based nucleic acid test

Image of Enterococcus sp. Photo courtesy of Janice Haney Carr.

Cara N. Wilder, Ph.D.

Enterococcus faecalis is a Gram-positive commensal bacterium known to inhabit the gastrointestinal tract of humans and animals. In immunologically compromised individuals, E. faecalis is a leading cause of urinary tract infections and nosocomial bacteraemia. This latter condition is of particular concern as it can lead to septic shock or the hematogenous spread of bacteria to other parts of the body, resulting in high rates of mortality and organ failure.

Unfortunately, the treatment of E. faecalis infection is not straightforward as a number of strains exhibit intrinsic and acquired resistance to a variety of antibiotics, including aminoglycosides, cephalosporins, and penicillins. Presently, these drug-resistant strains are commonly treated with vancomycin; however, in some instances the extended use of this antimicrobial drug has resulted in the emergence of vancomycin-resistant strains. To make matters worse, current treatment options for vancomycin-resistant strains is limited. Therefore, the rapid identification of vancomycin-resistant strains is imperative to the successful treatment of infection.

In recent years, advances in diagnostics have yielded a number of sensitive assays for the detection of E. faecalis, including fluorescent in situ hybridization (FISH), matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS), and the microarray-based Verigene Gram-Positive Blood Culture test (BC-GP) (Nanosphere). This latter method was recently validated through an examination of 12 Gram-positive targets including E. faecalis, as well as associated drug-resistance determinants. In this study, Buchan et al. used the Verigene BC-GP test to analyze 1,252 positive blood culture broths collected from five clinical centers throughout the United States. The resultant data indicated that the BC-GP test can sensitively and specifically identify E. faecalis and other leading causes of Gram-positive bacteremia directly from positive blood cultures. Further, this assay was capable of detecting the genetic markers vanA and vanB, which confer resistance to vancomycin. Overall, the Verigene BC-GP assay may prE. faecalis, ultimately enhancing public health.
ovide diagnosticians with a more sensitive means of detecting vancomycin-resistant

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