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The use of Gram stain and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry on positive blood culture: synergy between new and old technology

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Fuglsang‐Damgaard D, Nielsen CH, Mandrup E, Fuursted K. The use of Gram stain and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry on positive blood culture: synergy between new and old technology. APMIS 2011; 119: 681–88.

Matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) is promising as an alternative to more costly and cumbersome methods for direct identifications in blood cultures. We wanted to evaluate a simplified pre‐treatment method for using MALDI‐TOF‐MS directly on positive blood cultures using BacT/Alert blood culture system, and to test an algorithm combining the result of the initial microscopy with the result suggested by MALDI‐TOF‐MS. Using the recommended cut‐off score of 1.7 the best results were obtained among Gram‐negative rods with correct identifications in 91% of Enterobacteriaceae, 83% in aerobic/non‐fermentative Gram‐negative rods, whereas results were more modest among Gram‐positive cocci with correct identifications in 52% of Staphylococci, 54% in Enterococci and only 20% in Streptococci. Combining the results of Gram stain with the top reports by MALDI‐TOF‐MS, increased the sensitivity from 91% to 93% in the score range from 1.5 to 1.7 and from 48% to 85% in the score range from 1.3 to 1.5. Thus, using this strategy and accepting a cut‐off at 1.3 instead of the suggested 1.7, overall sensitivity could be increased from 88.1% to 96.3%. MALDI‐TOF‐MS is an efficient method for direct routine identification of bacterial isolates in blood culture, especially when combined with the result of the Gram stain.
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Document Type: Research Article

Affiliations: Department of Clinical Microbiology, Aarhus University Hospital, Skejby, Aarhus N, Denmark

Publication date: 2011-10-01

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