Blood Pathogens Rapidly Identified by Novel Molecular Methods

Rapid and accurate identification of pathogens responsible for sepsis, a life-threatening medical condition that is defined as systemic inflammatory response syndrome, is essential for early and targeted antimicrobial therapy.

Blood cultures represent the reference standard for the detection and identification of pathogens that cause bloodstream infections but conventional culture-based identification systems are time consuming but can be improved by using additional test systems.

Microbiologists at the Medical University of Graz (Austria) examined 103 positive blood cultures collected from December 2012 until March 2013. Blood cultures were obtained from patients with suspected sepsis as part of the standard hospital care and transferred to the laboratories.

The investigators evaluated the hemoFISH test using Beacon-Based Fluorescence in Situ Hybridization (bbFISH) technology for accurate identification of microorganisms in positive blood cultures by comparison with culture-based identification methods. The hemoFISH assay (miacom diagnostics, Inc.; Düsseldorf, Germany) is an in vitro diagnostic/Conformité Européene (CE) labeled test system that uses the bbFISH technology.

A total number of 103 positive blood culture bottles, with 59.0% grown in BACTEC Plus Aerobic/F and 41.0% BACTEC Plus Anaerobic/F (Becton Dickinson Diagnostic Systems; Franklin Lakes, NJ, USA), were tested. Culture-dependent identification with the use of the reference methods of mass spectrometry (MALDI-TOF MS Shimatzu Corporation; Kyoto, Japan) or Vitek2 (bioMérieux; Marcyl`Etoile, France) indicated that 95.1% of the blood culture bottles showed monomicrobial growth and 4.9% showed polymicrobial growth.

From the 106 bacterial species identified with the reference methods, the hemoFISH correctly identified 55.7% to species level, 34.0% to genus level, 7.5% to family level, and 2.8% were unidentifiable. The hemoFISH assay showed a sensitivity and specificity of 100%. From the 106 slides tested, in 11 cases the readout was initially challenging because of slight autofluorescence from certain probes. These slides were reevaluated and double-checked by a second investigator. In all cases, the result obtained by the two investigators was in agreement with the culture results. The specific fluorescence was much brighter than the observed autofluorescence.

The authors concluded that the hemoFISH assay that uses the novel bbFISH technology is an easy-to-handle, rapid, reliable tool for the identification of a broad range of microorganisms and facilitates the decision of antimicrobial therapy in septic patients. The study was published in the November 2013 issue of the Journal of Molecular Diagnostics.

Related Links:
Medical University of Graz
miacom diagnostics
Becton Dickinson Diagnostic Systems