Identification of microorganisms by FilmArray and matrix-assisted laser desorption ionization-time of flight mass spectrometry prior to positivity in the blood culture system

Abstract

In this study, we investigated the performance of the FilmArray and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) in identifying microorganisms from blood culture (BC) bottles prior to positivity. First, we used simulated BacT/Alert FA Plus BC bottles with five each for Escherichia coli and Staphylococcus aureus isolates. The FilmArray identified all 10 isolates before BC positivity with 9/10 at 5 h and 1 at 7.5 h after incubation in the BC system. MALDI-TOF MS failed to identify the isolates prior to positivity. When the bottles were incubated for 2.5 h at room temperature (RT) before we put them into the BC system, the FilmArray identified 6/10 at 2.5 h and the remaining 4 at 5 h. Finally, we tested simulated BC bottles after incubation at RT. Interestingly, 9/10 isolates were identified with the FilmArray after 8 h of incubation at RT. Second, we studied clinical BC bottles in quadruplicate. When three-fourths of the parallel bottles signaled positive, the FilmArray was run on the fourth nonsignaled bottle and was found to be positive in 14/15 such cases. Third, we analyzed the performance of the FilmArray in the identification of microorganisms from clinical BC bottles before incubation in the system. Two milliliters of broth from 400 BC bottles was collected after arrival at the laboratory and stored at -70°C. Sixteen bottles later signaled positive in the system. When the frozen broth from these bottles was analyzed, the FilmArray identified all the microorganisms in 8/16 bottles prior to incubation in the BC system. This study shows that the FilmArray can identify microorganisms from BC bottles prior to positivity and in some cases even prior to incubation in the BC system.

FIG 1

Flow chart of in vitro studies of the FilmArray (FA) and MALDI-TOF MS on BacT/Alert FA Plus blood culture bottles inoculated with Escherichia coli (n = 5) and Staphylococcus aureus (n = 5).

FIG 2

Flow chart of clinical blood culture bottles tested with the FilmArray (FA) prior to positivity in the blood culture system (A) and prior to incubation in the blood culture system (B).