[Rapid identification and susceptibility testing of Gram-positive cocci in BacT/ALERT blood cultures by direct inoculation into the Vitek 2 system]

Abstract

Introduction: To provide the clinician with early information about blood culture results allows a better prognosis and a reduced mortality rate of the patient with sepsis. In order to contribute to this aim, we performed a study for the identification and susceptibility profiling of positive blood cultures by direct inoculation into the automated Vitek 2 system.

Materials and methods: Blood cultures of 57 patients with monomicrobial bacteriaemia due to gram-positive cocci were evaluated. Addition of saponin to the fluid from blood culture bottles was performed prior to the inoculation of Vitek 2 system cards. The same samples were also examined with the standard method starting from agar plate grown subcultures.

Results: Comparison between the results obtained with the standard method and the direct method revealed that 82% of the samples were correctly identified and that 97% of the isolates showed a concordant antimicrobial susceptibility profile for all drugs tested. Compared to the standard method, the very major error rate of the direct method was just 0.5%, the major error rate was 0.5%, and the minor error rate was 2%.

Conclusion: These data suggest that addition of saponin to the fluid from blood culture bottles of the BacT/ALERT(®) 3D before inoculation of the appropriate Vitek 2 cards leads to the rapid and reliable identification and susceptibility profiling of gram-positive cocci in blood samples. Compared to the standard method, the direct method would reduce turnaround time by at least 24 hours.