Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) bacterial identification has revolutionized clinical microbiology. Typically, bacteria must be first cultured prior to identification; however, several techniques have emerged that allow the identification of bacteria directly from certain specimen types, including blood cultures. The aim of this study was to compare a direct MALDI-TOF MS identification technique of positive blood cultures with those having at least 4-6 hours of sufficient growth
Only blood cultures flagged overnight as positive by the BD Bactec® were included for study. A one ml aliquot was drawn and immediately processed using a lysis centrifugation technique and analyzed using MALDI-TOF (bioMérieux). Positive blood culture samples were also sub-cultured onto agar plates as per standard laboratory practice, incubated for 4-6 hours and if sufficient growth was present, processed using MALDI-TOF. Cultures with insufficient growth are incubated overnight. Direct identifications were compared to those where sufficient growth was achieved
Between June 2015 to February 2016, 300 positive blood cultures were included for study. Of these there were 156 Gram positive cocci, 112 Gram negative bacilli, 15 anaerobic organisms, 11 Gram positive bacilli and 6 yeast. Using a confidence threshold of 99.9%, 69% of all organisms were correctly identified using the direct identification method. The identification of any organism with a confidence threshold <99.9% was not accepted. Approximately 81% of Gram negative bacilli were correctly identified compared with 64% of Gram positive cocci 36% of Gram positive bacilli.
The lysis-centrifugation direct identification method is a relatively inexpensive ($1.00) and rapid technique that will allow clinicians to receive the identification of organisms from approximately 70% of bacteremic patients 6 to 24 hours early than waiting for sufficient growth. This should allow clinicians to make better informed empiric antimicrobial choices to manage their patients.
H. Al Sidairi,
J. Head, None
R. Davidson, None
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