Effect of humidity during sample preparation on bacterial identification using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Impact of direct identification of bacteria in blood culture-positive specimens by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry on physician selection of antimicrobial therapy

BACKGROUND

Rapid identification of the causative organism in blood stream infections is essential for early initiation of appropriate antimicrobial therapy. Direct identification of bacteria in positive blood culture bottles using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry is a promising application. A variety of direct identification methods have been reported; however, few studies have evaluated the impact of these methods on physician decision making regarding antimicrobial therapy.

METHODS

We developed a simple method for direct bacterial identification and applied it to daily clinical practice to investigate the impact of direct identification of bacteria in positive blood culture bottles on physicians' choice of antimicrobial agents for treatment.

RESULTS

From January 2016 to December 2022, we attempted direct identification in 98 cases and successfully acquired identification results in 88 cases. In three cases, no empiric antimicrobial agents were initiated at the time of venipuncture for blood culture but later initiated based on the direct identification results. In the remaining 85 cases, empiric antimicrobial therapy was initiated at the time blood cultures were performed, and in 29 cases, empiric antimicrobial therapy was changed after direct identification. In 17 of these 29 cases, the antimicrobial therapy was changed based on the direct identification of bacterial genus/species, resulting in a change to an effective antimicrobial therapy before the antimicrobial susceptibility testing results were available.

CONCLUSIONS

Direct identification of bacteria from positive blood culture bottles could contribute to earlier selection of or changes to antimicrobial therapies by attending physicians.

Enhanced Water Sorption Performance of Polyacrylamide & Glass Fiber Paper Composites: Investigation and Comparison of Application in Desiccant Wheels

The water sorption and desorption properties of solid adsorbent materials are crucial in rotary dehumidification systems. Metal organic frameworks (MOFs) and hydrogels are mostly at the laboratory stage due to factors like the synthesis process and yield. In this study, we utilized an eco-friendly and large-scale synthesis method to prepare polyacrylamide (PAM) hydrogels (yielding approximately 500 mL from a single polymerization). Subsequently, PAM was then coated onto glass fiber paper (GFP), which serves as a commonly employed substrate in desiccant wheels. By incorporating the hygroscopic salt LiCl and optimizing the content of each component, the water sorption performance of the composite was notably improved. The water sorption and desorption performances, as well as cycling stability, were evaluated and compared with composites containing aluminum fumarate, LiCl, and GFP (AlFum-LiCl&GFP). The results revealed that PAM-LiCl&GFP outperformed AlFum-LiCl&GFP in terms of sorption capacity throughout various relative humidity (RH) levels. It achieved a water uptake of 1.06 g·g-1 at 25 °C and 30% RH, corresponding to a water sorption rate coefficient K of 15.32 × 10-4 s-1. Furthermore, the lower desorption temperature (60 °C) resulting in a desorption ratio of 82.6%, along with the excellent cycling stability and effective performance as a desiccant wheel module, provide evidence for the potential application of PAM-LiCl&GFP in desiccant wheels.

Mass Spectral Imaging to Map Plant-Microbe Interactions

Plant-microbe interactions are of rising interest in plant sustainability, biomass production, plant biology, and systems biology. These interactions have been a challenge to detect until recent advancements in mass spectrometry imaging. Plants and microbes interact in four main regions within the plant, the rhizosphere, endosphere, phyllosphere, and spermosphere. This mini review covers the challenges within investigations of plant and microbe interactions. We highlight the importance of sample preparation and comparisons among time-of-flight secondary ion mass spectroscopy (ToF-SIMS), matrix-assisted laser desorption/ionization (MALDI), laser desorption ionization (LDI/LDPI), and desorption electrospray ionization (DESI) techniques used for the analysis of these interactions. Using mass spectral imaging (MSI) to study plants and microbes offers advantages in understanding microbe and host interactions at the molecular level with single-cell and community communication information. More research utilizing MSI has emerged in the past several years. We first introduce the principles of major MSI techniques that have been employed in the research of microorganisms. An overview of proper sample preparation methods is offered as a prerequisite for successful MSI analysis. Traditionally, dried or cryogenically prepared, frozen samples have been used; however, they do not provide a true representation of the bacterial biofilms compared to living cell analysis and chemical imaging. New developments such as microfluidic devices that can be used under a vacuum are highly desirable for the application of MSI techniques, such as ToF-SIMS, because they have a subcellular spatial resolution to map and image plant and microbe interactions, including the potential to elucidate metabolic pathways and cell-to-cell interactions. Promising results due to recent MSI advancements in the past five years are selected and highlighted. The latest developments utilizing machine learning are captured as an important outlook for maximal output using MSI to study microorganisms.

Sample preparation and culture condition effects on MALDI-TOF MS identification of bacteria: A review

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an excellent tool for bacterial identification. It allows high throughput, sensitive and specific applications in clinical diagnostics and environmental research. Currently, there is no optimal standardized protocol for sample preparation and culture conditions to profile bacteria. The performance of MALDI-TOF MS is affected by several variables, such as sample preparation, culture media and culture conditions, incubation time/growth stage, incubation temperature, high salt content, blood in the culture media, and others. This review thus aims to clarify why a uniformed protocol is not plausible, to assess the effects these factors have on MALDI-TOF MS identification score, and discuss possible optimizations for its methodology, in relation to specific bacterial representatives and strain requirements.