CHEAP AND RAPID IN-HOUSE METHOD FOR DIRECT IDENTIFICATION OF POSITIVE BLOOD CULTURES BY MALDI-TOF MS TECHNOLOGY

tamar leshem ¹ Yoram Keness ^2,3 Orna Nitzan ^4,5 Nina Pastukh ¹ Linda Tkhawkho ¹ Victoria Freidus ¹ Avi Peretz ^1,4

¹Clinical Microbiology Laboratory, Baruch Padeh Medical Center, Poriya, Israel
²Clinical Microbiology Laboratory, Ziv Medical Center, Zefat, Israel
³Clinical Microbiology Laboratory, Emek Medical Center, Afula, Israel
⁴Faculty of Medicine, Bar Ilan University, Galilee, Israel
⁵Unit of Infectious Diseases, Baruch Padeh Medical Center, Poriya, Israel

Background: Rapid and accurate pathogen identification in blood cultures is very important for septic patients and has major consequences on sepsis morbidity and mortality rates. In recent years, matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS)-based technology has become useful for highly specific and sensitive identification of bacteria and yeasts from clinical samples including sterile body fluids. Additional in-house methods enabled direct identification from blood cultures following various preparation protocols.

Methods: Blood culture (5 ml) was harvested from each bottle following microorganism growth identification by BACTEC^TMFX system and transferred into a VACUETTE^®Z Serum Sep Clot Activator tube containing an inert gel, which following centrifugation separates microorganisms from the blood cells. We used MALDI-TOF MS analysis for identification of microorganisms collected from the gel surface.

Results: Positive blood culture bottles (186) were collected. In comparison with the routine method, 99% (184/186) and 90% (168/186) of the isolates were correctly identified by the SepsiTyper kit and the in-house method, respectively. We found high concordance (Pearson coefficient=0.7, p<0.0001) between our in-house method and the SepsiTyper kit. Additionally, high correlation was found in sub-groups of identified bacteria, with Pearson coefficients of 0.77 (p<0.0001), 0.67 (p<0.0001), and 0.73 (p<0.007) for Gram negative, Gram positive, and anaerobic bacteria, respectively.

Conclusions: Our in-house method was found to be in good agreement with the SepsiTyper kit. Considering the low costs and the rapid and easy implementation of this procedure, we propose our in-house method for the direct identification of bacteria and yeasts from blood cultures.