Direct identification of bacteria from charcoal-containing blood culture bottles using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.
Several protocols for direct matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) from positive blood cultures are currently used to speed up the diagnostic process of bacteraemia. Identification rates are high and results are accurate for the BACTEC™ system and for charcoal-free bottles. Only a few studies have evaluated protocols for charcoal-containing BacT/ALERT bottles reaching substantially lower identification rates. We established a new protocol for sample preparation from aerobic and anaerobic positive charcoal-containing BacT/ALERT blood culture bottles and measured the protein profiles (n = 167). Then, we integrated this protocol in the routine workflow of our laboratory (n = 212). During the establishment of our protocol, 74.3 % of bacteria were correctly identified to the species level, in 23.4 %, no result and in 2.4 %, a false identification were obtained. Reliable criteria for correct species identification were a score value ≥1.400 and a best match on rank 1-3 of the same species. Identification rates during routine workflow were 77.8 % for correct identification, 20.8 % for not identified samples and 1.4 % for discordant identification. In conclusion, our results indicate that MALDI-TOF MS is possible, even from charcoal-containing blood cultures. Reliable criteria for correct species identification are a score value ≥1.400 and a best match on rank 1-3 of a single species.
Institute of Medical Microbiology and Hygiene, University Medical Centre Freiburg, Hermann-Herder-Straße 11, 79104 Freiburg, Germany. nicole.wueppenhorst@uniklinik-freiburg.de
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N
Wüppenhorst
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Consoir
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Lörch
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Schneider
D016470:Bacteremia / Q000175:diagnosis* / Q000382:microbiology; D001420:Bacteria, Aerobic / Q000145:classification / Q000302:isolation & purification*; D001421:Bacteria, Anaerobic / Q000145:classification / Q000302:isolation & purification*; D001426:Bacterial Proteins / Q000032:analysis; D001431:Bacteriological Techniques / Q000379:methods; D002606:Charcoal; D004755:Enterobacteriaceae / Q000145:classification / Q000302:isolation & purification; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013210:Staphylococcus / Q000145:classification / Q000302:isolation & purification; D013291:Streptococcus / Q000145:classification / Q000302:isolation & purification; D013997:Time Factors
D001426:Bacterial Proteins; D011933:Reagent Kits, Diagnostic; D002606:Charcoal