Mass spectrometry-based microbiological testing for blood stream infection.

The most successful application of mass spectrometry (MS) in laboratory medicine is identification (ID) of microorganisms using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) in blood stream infection. We describe MALDI-TOF MS-based bacterial ID with particular emphasis on the methods so far developed to directly identify microorganisms from positive blood culture bottles with MALDI-TOF MS including our own protocols. We touch upon the increasing roles of Liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) as well. Because blood culture bottles contain a variety of nonbacterial proteins that may interfere with analysis and interpretation, appropriate pretreatments are prerequisites for successful ID. Pretreatments include purification of bacterial pellets and short-term subcultures to form microcolonies prior to MALDI-TOF MS analysis. Three commercial protocols are currently available: the Sepsityper® kit (Bruker Daltonics), the Vitek MS blood culture kit (bioMerieux, Inc.), and the rapid BACpro® II kit (Nittobo Medical Co., Tokyo). Because these commercially available kits are costly and bacterial ID rates using these kits are not satisfactory, particularly for Gram-positive bacteria, various home-brew protocols have been developed: 1. Stepwise differential sedimentation of blood cells and microorganisms, 2. Combination of centrifugation and lysis procedures, 3. Lysis-vacuum filtration, and 4. Centrifugation and membrane filtration technique (CMFT). We prospectively evaluated the performance of this CMFT protocol compared with that of Sepsityper® using 170 monomicrobial positive blood cultures. Although preliminary, the performance of the CMFT was significantly better than that of Sepsityper®, particularly for Gram-positive isolates. MALDI-TOF MS-based testing of polymicrobial blood specimens, however, is still challenging. Also, its contribution to assessment of susceptibility and resistance to antibiotics is still limited. For this purpose, liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) should be more useful because this approach can identify as many as several thousand peptide sequences. MALDI-TOF MS is now an essential tool for rapid bacterial ID of pathogens that cause blood stream infection. For the purpose of assessment of susceptibility and resistance to antibiotics of the pathogens, the roles of liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) will increase in the future.

Nomura F ，Tsuchida S ，Murata S ，Satoh M ，Matsushita K ... -  《-》

Application of the biocopolymer preparation system, rapid BACpro® II kit, for mass-spectrometry-based bacterial identification from positive blood culture bottles by the MALDI Biotyper system.

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is increasingly used for identification of microorganisms from positive blood cultures. Pretreatments to effectively remove non-bacterial components and selectively collect microorganisms are a prerequisite for successful identification, and a variety of home-brew and commercial protocols have been reported. Although commercially available kits, mainly the Sepsityper Kit, are increasingly used, the identification rates reported often are not satisfactory, particularly for Gram-positive isolates. We recently developed a method to collect bacteria from positive blood culture bottles using a polyallylamine-polystyrene copolymer that has been used in wastewater processing. This pretreatment protocol is now commercially available as the rapid BACpro® II kit (Nittobo Medical Co., Tokyo, Japan). The operation time required for processing using this novel kit is approximately 10 min, and the entire procedure can be completed within a biosafety cabinet. Since the performance of the rapid BACpro® II kit has not been tested using the MALDI Biotyper system, we prospectively evaluated the performance of the rapid BACpro® II kit as compared with the Sepsityper® kit. Performance of the rapid BACpro® II kit was evaluated using a total of 193 monomicrobial cases of positive blood culture. Medium from blood culture bottles was pretreated by the rapid BACpro® II kit or the Sepsityper® Kit, and isolated cells were subjected to direct identification by MS fingerprinting in parallel with conventional subculturing for reference identification. The overall MALDI-TOF MS-based identification rates with >1.7 score and >2.0 score obtained using the rapid BACpro® II kit were 99.5% and 80.8%, respectively, whereas those obtained using the Sepsityper® Kit were 89.1% and 68.4%, respectively (P < 0.05 for >1.7 and P < 0.05 for >2.0 by Pearsons's chi-square). In Gram-positive cases, the rapid BACpro® II kit gave identification rate of 100% with >1.7 score and 69.4% with >2.0 score, whereas there were 84.7% and 56.8%, respectively by the Sepsityper® Kit (P < 0.05 for >1.7). These results are preliminary, but considering that this new kit is easy to perform and the identification rates are promising, the rapid BACpro® II kit deserves assessment in a larger-scale study with a variety of platforms for MS-based bacterial identification.

Tsuchida S ，Murata S ，Miyabe A ，Satoh M ，Takiwaki M ，Ashizawa K ，Terada T ，Ito D ，Matsushita K ，Nomura F ... -  《-》

Comparison of rapid BACpro® II, Sepsityper® kit and in-house preparation methods for direct identification of bacteria from blood cultures by MALDI-TOF MS with and without Sepsityper® module analysis.

Kayin M ，Mert B ，Aydemir S ，Özenci V ... -  《-》

An in-house centrifugation and membrane filtration technique for identifying microorganisms from positive blood culture bottles with high identification rates using matrix-assisted laser desorption ionization-Time-of-flight mass spectrometry: A preliminar

Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) is one of the most promising technologies for the identification of microbial pathogens directly from positive blood culture bottles. As blood culture bottle medium contains various nonbacterial proteins, including those derived from blood cells, pretreatment to effectively remove host cells is key for successful proteome-based identification of microorganisms. Although the Sepsityper® kit is the most widely used pretreatment protocol, its performance is not satisfactory, particularly for gram-positive isolates. We developed a new in-house protocol, the centrifugation and membrane filtration technique (CMFT), in which vacuum-filtration is coupled with differential centrifugation. We prospectively evaluated the performance of this novel method compared with that of the Sepsityper®. For gram-negative bacterial isolates, the species-level identification rates obtained with the CMFT and the Sepsityper® were comparable (98.8% vs 92.9%). By contrast, for gram-positive isolates, the performance of the CMFT was significantly better than that of the Sepsityper® (P < 0.05). Using our new protocol, 81 (95.3%) isolates were identified with a score >2.0, and 85 (100%) isolates were identified with a score >1.7, versus 46 (54.1%) and 69 (81.2%), respectively, for the Sepsityper®. These results are preliminary, but considering that this novel protocol provides notably high species-level identification rates for gram-positive isolates, it deserves assessment in a larger-scale study with a variety of platforms for MS-based identification of microorganisms.

Tsuchida S ，Murata S ，Miyabe A ，Satoh M ，Takiwaki M ，Matsushita K ，Nomura F ... -  《-》

An improved in-house lysis-filtration protocol for bacterial identification from positive blood culture bottles with high identification rates by MALDI-TOF MS.

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is now a well-established method for identification of microorganisms from positive blood cultures. Pretreatments to effectively remove non-bacterial proteins are a prerequisite for successful identification, and a variety of protocols have been reported. Although commercially available kits, mainly the Sepsityper Kit, are increasingly used, the identification rates reported often are not satisfactory, particularly for Gram-positive isolates. We developed a new, in-house lysis-filtration protocol and prospectively evaluated its performance compared to the Sepsityper kit. The in-house protocol consists of three simple steps: lysis by ammonium chloride, aspiration with a syringe fitted with a 0.45-μm membrane, and centrifugation to collect microbes. The novel protocol requires only 20 min. Performance of the in-house protocol was evaluated using a total of 117 monomicrobial cases of positive blood culture. Medium from blood culture bottles was pretreated by the in-house protocol or the commercial kit, and isolated cells were subjected to direct identification by mass spectrometry fingerprinting in parallel with conventional subculturing for reference identification. The overall MALDI-TOF MS-based identification rates with score > 1.7 and > 2.0 obtained using the in-house protocol were 99.2% and 85.5%, respectively, whereas those obtained using the Sepsityper Kit were 85.4% and 61.5%, respectively. For Gram-positive cases, the in-house protocol yielded scores >1.7 and > 2.0 at 98.5% and 76.1%, respectively, whereas the commercial kit yielded these scores at 76.1% and 43.3%, respectively. Although these are preliminary results, these values suggest that this easy lysis-filtration protocol deserves assessment in a larger-scale test.

Tsuchida S ，Murata S ，Miyabe A ，Satoh M ，Takiwaki M ，Matsushita K ，Nomura F ... -  《-》