Rapid Identification of Bacteria in Positive Blood Culture Broths by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

Abstract

Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry is a rapid, accurate method for identifying bacteria and fungi recovered on agar culture media. We report herein a method for the direct identification of bacteria in positive blood culture broths by MALDI-TOF mass spectrometry. A total of 212 positive cultures were examined, representing 32 genera and 60 species or groups. The identification of bacterial isolates by MALDI-TOF mass spectrometry was compared with biochemical testing, and discrepancies were resolved by gene sequencing. No identification (spectral score of <1.7) was obtained for 42 (19.8%) of the isolates, due most commonly to insufficient numbers of bacteria in the blood culture broth. Of the bacteria with a spectral score of >1.7, 162 (95.3%) of 170 isolates were correctly identified. All 8 isolates of Streptococcus mitis were misidentified as being Streptococcus pneumoniae isolates. This method provides a rapid, accurate, definitive identification of bacteria within 1 h of detection in positive blood cultures with the caveat that the identification of S. pneumoniae would have to be confirmed by an alternative test.In the early 1970s the first semiautomated blood culture system, the radiometric Bactec system, was introduced into the clinical microbiology laboratory. In subsequent years this system was refined with the development of fully automated, closed, continuously monitoring systems for the detection of microbial growth. Recently, a commercial real-time PCR system (LightCycler SeptiFast; Roche Molecular Systems) was introduced with the hope that culture-based systems could be replaced with this technology; however, initial reports documented that this system can be used as a complement to but not a replacement for the current generation of automated systems (16,17,19). Because culture-based systems will be used in the near future, accurate, rapid identification methods are still needed. As with blood culture systems, a transition in identification systems began in the early 1970s with the introduction of commercial biochemical strips and panels and then with the rapid development and refinement of automated instruments that inoculate, incubate, interpret, and report microbial identifications. Currently, most bacteria and fungi can be identified with these systems in a few hours to 1 to 2 days, with slow-growing or metabolically inert organisms requiring additional time or supplementary tests. The identification of organisms recovered in blood culture broths requires an initial subculture of the broth and overnight incubation to obtain isolated colonies for further testing or the concentration of the bacteria or fungi by centrifugation before further processing. In general, the approach of concentrating organisms by centrifugation and then identification by rapid biochemical tests (1a), fluorescent in situ hybridization (FISH) (4, 6, 15, 18), or commercial biochemical systems is accurate, although the limitations of incubation delays, the need for supple...

Molecular-based Screening for Perinatal Group B Streptococcal Infection: Implications for Prevention and Therapy

“…MALDI-TOF MS has revolutionized clinical microbiology by allowing a rapid, accurate, and cheap identification of bacteria, including GBS [54]. In a recent study on 212 positive blood vials, MALDI-TOF MS yielded a good spectrum for 80 % of vials, with an accurate bacterial characterization of [95 % [55].…”

An Evaluation Of Direct Identification Of Pathogens From Blood Cultures By Maldi-Tof Mass Spectrometry

“…Identification of microorganisms from positive blood culture using of MALDI Sepsity per processing kit requires approximately 20 minutes and it does independent of species (6, 10,13,18,20,25,26,32,33). Batch processing added approximately 1 min per blood culture analyzed.Our estimated time to identify bacteria from the positive blood culture, of fixed automated system BD BACTEC Fx signal time to MALDI-TOF mass spectrometry identification time, is not an objective, it includes the blood smear preparation time by Gram staining, …”

“…With a special set of MALDI Sepsityper is possible to identify bacteria directly from the positive blood culture (17)(18)(19)(20)(21)(22)(23)(24)(25). Most reports describe the blood culture must be grown in automated BACTEC system vials (26,27).…”

Utilisation en routine du MALDI-TOF-MS pour l’identification des pathogènes en microbiologie médicale

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