title: 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.
abstract: 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.
authors.affiliation: Department of Clinical Microbiology, Aarhus University Hospital, Skejby, Denmark. dfd@rn.dk
authors.forename: David
authors.initials: D
authors.lastname: Fuglsang-Damgaard
authors.forename: Camilla Houlberg
authors.initials: CH
authors.lastname: Nielsen
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Mandrup
authors.forename: Kurt
authors.initials: K
authors.lastname: Fuursted
mesh_terms: D016470:Bacteremia / Q000097:blood* / Q000382:microbiology*; D001419:Bacteria / Q000737:chemistry / Q000302:isolation & purification*; D001431:Bacteriological Techniques / Q000379:methods*; D001769:Blood / Q000382:microbiology; D005840:Gentian Violet; D006801:Humans; D010619:Phenazines; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods* / Q000592:standards
chemical_list: C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet