Multicenter Evaluation of Rapid BACpro® II for the Accurate Identification of Microorganisms Directly from Blood Cultures Using MALDI-TOF MS

Evolving strategies in microbe identification-a comprehensive review of biochemical, MALDI-TOF MS and molecular testing methods

Detection and identification of microorganisms are the first steps to guide susceptibility testing and enable clinicians to confirm diseases and guide therapy. The faster the pathogen identification is determined, the quicker the appropriate treatment can be started. In the clinical microbiology laboratory, multiple methodologies can be used to identify organisms, such as traditional biochemical testing or more recent methods like MALDI TOF MS and nucleic acid detection/identification assays. Each of these techniques has advantages and limitations, and clinical laboratories need to determine which methodology is best suited to their particular setting in terms of clinical needs, availability of technical expertise and cost. This article presents a concise review of the history, utilization, advantages and limitations of the main methods used for identifying microorganisms in microbiology laboratories.

Comparison of Zybio Kit and saponin in-house method in rapid identification of bacteria from positive blood cultures by EXS2600 matrix-assisted laser desorption ionization time-of-flight mass spectrometry system

We evaluated the performance of Zybio EXS2600 matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) (Zybio Inc., Chongqing, China) for the identification of bacteria from positive blood culture (BC) bottles using Blood Culture Positive Sample Pretreatment Kit (Zybio Inc., Chongqing, China) in comparison to an in-house saponin method. Following a positive signal by the BACTEC™ FX system, confirmation of identification was achieved using subcultured growing biomass used for MALDI-TOF MS analysis. A total of 94 positive BC bottles with 97 bacterial isolates were analyzed. The overall identification rates at the genus and species levels for the saponin method were 89.7% (87/97) and 74.2% (72/97), respectively. With the Zybio Kit, 88.7% (86/97) and 80.4% (78/97) of microorganisms were correctly identified to the genus and species levels, respectively. The saponin method identified 65.3% (32/49) of Gram-positive bacteria at the species level, whereas the Zybio Kit achieved a higher species-level identification rate of 79.6% (39/49) (p = 0.1153). The saponin method with additional on-plate formic acid extraction showed a significantly higher overall identification rate in comparison to the saponin method without that step for both genus (87.6% [85/97] vs. 70.1% [68/97], p = 0.0029) and species level (70.1% [68/97] vs. 46.4% [45/97], p = 0.0008). Identification rates of Gram-negative bacteria showed a higher identification rate, however, not statistically significant with additional Zybio Kit protocol step on both genus (85.4% [41/48] vs. 81.3% [39/48], p = 0.5858) and species level (77.1% [37/48] vs. 75% [36/48], p = 0.8120). Zybio Kit could offer an advantage in species-level identification, particularly for Gram-positive bacteria. The inclusion of on-plate formic acid extraction in the saponin method notably enhanced identification at both genus and species levels for Gram-positive bacteria. The extended protocol provided by the Zybio Kit could potentially offer an advantage in the identification of Gram-negative bacteria at both genus and species levels. Enhancements to the Zybio EXS2600 MALDI-TOF instrument software database are necessary.

Non-electrostatic interactions associated with aggregate formation between polyallylamine and Escherichia coli

Bacterial aggregation by mixing with polymers is applied as pretreatment to identify pathogens in patients with infectious diseases. However, the detailed interaction between polymers and bacteria has yet to be fully understood. Here, we investigate the interaction between polyallylamine and Escherichia coli by isothermal titration calorimetry. Aggregation was observed at pH 10 and the binding was driven by favorable enthalpic gain such as the electrostatic interaction. Neither aggregation nor the apparent heat of binding was observed at pH 4.0, despite the strong positive charge of polyallylamine. These results suggest that intermolecular repulsive forces of the abundant positive charge of polyallylamine cause an increased loss of conformational entropy by binding. Non-electrostatic interaction plays a critical role for aggregation.

Sepsityper® Kit versus In-House Method in Rapid Identification of Bacteria from Positive Blood Cultures by MALDI-TOF Mass Spectrometry

In order to further accelerate pathogen identification from positive blood cultures (BC), various sample preparation protocols to identify bacteria with MALDI-TOF MS directly from positive BCs have been developed. We evaluated an in-house method in comparison to the Sepsityper® Kit (Bruker Daltonics, Bremen, Germany) as well as the benefit of an on-plate formic acid extraction step following positive signal by the BACTECTM FX system. Confirmation of identification was achieved using subcultured growing biomass used for MALDI-TOF MS analysis. A total of 113 monomicrobial positive BCs were analyzed. The rates of Gram-positive bacteria correctly identified to the genus level using in-house method and Sepsityper® Kit were 63.3% (38/60) and 81.7% (49/60), respectively (p = 0.025). Identification rates at species level for Gram-positive bacteria with in-house method and Sepsityper® kit were 30.0% (18/60) and 66.7% (40/60), respectively (p < 0.001). Identification rates of Gram-negative bacteria were similar with the in-house method and Sepsityper® Kit. Additional on-plate formic acid extraction demonstrated significant improvement in the identification rate of Gram-positive bacteria at both genus and species level for both in-house (p = 0.001, p < 0.001) and Sepsityper® Kit methods (p = 0.007, p < 0.001). Our in-house method is a candidate for laboratory routines with Sepsityper® Kit as a back-up solution when identification of Gram-positive bacteria is unsuccessful.