![]() ![]() The matrix assisted laser desorption-ionization time of flight mass spectrometry (MALDI-TOF MS) is a novel method for the direct identification of pathogens in blood culture broths, with results available within 2 hours. These assays, however, only target specific organisms require technical expertise and specimens are usually processed in batches. Rapid nucleic acid amplification methods such as real-time PCR using melting curve analysis, multiplex PCR, fluorescence in situ hybridization (FISH) and peptide nucleic acid-FISH (PNA-FISH) have been used to detect pathogens in blood cultures including Staphylococcus aureus, Enterococcus faecalis and Candida albicans. Pathogens with fastidious growth requirements and those difficult to identify by phenotypic methods require more time for identification. Traditional phenotypic based diagnostic methods for BSIs require the detection of bacterial growth in blood culture broths, followed by species identification and antimicrobial susceptibility testing (turnaround time 24–48 hours after initial growth). Rapid, accurate identification of the etiologic pathogen is critical for guiding effective antimicrobial therapy and improving patient outcomes, and for reducing length of hospitalization and hospital costs. In the first six hours of septic shock, each hour of delay in initiating effective antimicrobial therapy following the onset of hypotension is associated with a reduction in average survival by 7.6%. In Australia, in-hospital mortality for patients presenting with septic shock ranges from 23.1–27.6%. In the United States, septicemia has consistently featured in the top 10 causes of death, accounting for 35,587 deaths (11.6 per 10 5 population) in 2009 alone. A diagnostic algorithm for positive blood culture broths that incorporates gram staining and MALDI-TOF MS should identify the majority of pathogens, particularly to genus level.īloodstream infections (BSIs) are a significant cause of morbidity and mortality in hospitals. Positive predictive values for the direct identification of both gram-positive and gram-negative bacteria from monomicrobial blood culture broths to genus level were 100%. Five blood cultures were misidentified, but at species level only including four monomicrobial blood cultures with Streptococcus oralis/ mitis that were misidentified as Streptococcus pneumoniae. Significantly more gram-negative organisms were identified compared to gram-positive organisms at species level (p<0.0001). Spectral scores <1.700 (no identification) were obtained in 128/507 (25.2%) positive blood culture broths, including 31.6% and 32.3% of gram-positive and polymicrobial blood cultures, respectively. Five hundred and seven positive blood culture broths were prospectively examined, of which 379 (74.8% 358 monomicrobial, 21 polymicrobial) were identified by MALDI-TOF MS 195 (100%) and 132 (67.7%) of 195 gram-positive and 163 (100%) and 149 (91.4%) of 163 gram-negative organisms from monomicrobial blood cultures were correctly identified to genus and species level, respectively. We evaluate for the first time, the performance of the MALDI Sepsityper™ Kit and MS for the identification of bacteria compared to standard phenotypic methods using the manufacturer's specified bacterial identification criteria (spectral scores ≥1.700–1.999 and ≥2.000 indicated identification to genus and species level, respectively). Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a novel method for the direct identification of bacteria from blood culture broths.
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