Use of a sample injection loop for an accurate measurement of particle number concentration by flow cytometry

Flow cytometry plays a pivotal role in biotechnology by providing quantitative measurements for a wide range of applications. Nonetheless, achieving precise particle quantification, particularly without relying on counting beads, remains a challenge. In this study, we introduce a novel exhaustive counting method featuring a sample loop-based injection system that delivers a defined sample volume to a detection system to enhance quantification in flow cytometry. We systematically assess the performance characteristics of this system with micron-sized polystyrene beads, addressing issues related to sample introduction, adsorption, and volume measurement. Results underscore the excellent analytical performance of the proposed method, characterized by high linearity and repeatability. We compare our approach to counting bead-based measurements, and while an approximate bias value was observed, the measured values were found to be similar between the methods, demonstrating its comparability and reliability. This method holds great promise for improving the accuracy and precision of particle quantification in flow cytometry, with implications for various fields including healthcare and environmental monitoring.

Multimodal Magneto-Fluorescent Nanosensor for Rapid and Specific Detection of Blood-Borne Pathogens

Detection of bacterial contaminants in blood and platelet concentrates (PCs) continues to be challenging in clinical settings despite available current testing methods. At the same time, it is important to detect the low bacterial contaminants present at the time of transfusion. Herein, we report the design and synthesis of a dual-modal magneto-fluorescent nanosensor (MFnS) by integrating magnetic relaxation and fluorescence modalities for the wide-range detection of blood-borne pathogens. In this study, functional MFnS are designed to specifically detect Staphylococcus epidermidis and Escherichia coli, two of the predominant bacterial contaminants of PCs. Specific interaction between the target pathogen and functional MFnS resulted in the change of water proton's magnetic relaxation time (T2 MR), indicative of sensitive detection of the target bacteria from low to high colony forming unit (CFU). In addition, the acquired MR signal of MFnS further facilitated the quantitative assessment of the slow and fast growth kinetics of target pathogens. Moreover, the presence of fluorescence modality in MFnS allowed for the detection of multi-contaminants. The bacterial detection was also performed in complex media including whole blood and platelet concentrates, which further demonstrated for it's robust detection sensitivity. Overall, our study indicated that the designer MFnS will have potential for the wide-range detection of blood-borne pathogens, and features desirable qualities including timeliness, sensitivity and, specificity.

Detection and counting of a submicrometer particle in liquid flow by self-mixing microchip Yb:YAG laser velocimetry

We observed intermittent modulation by scattered light from a single submicrometer particle moving in the flow channel using a self-mixing microchip Yb:YAG laser Doppler velocimeter (LDV) under lateral beam access. The Doppler-shift frequency chirping (i.e., velocity change) was identified in accordance with a particle passage through the beam focus. Single particle counting, which obeys the Poisson distribution, was performed successfully over a long period of time. The experimental results have been reproduced by a numerical simulation. The LDV signal was increased over 20 dB for a 202-nm particle without chirping by collinear beam access with the laser beam axis aligned along the flow direction.

Bench Test for the Detection of Bacterial Contamination in Platelet Concentrates Using Rapid and Cultural Detection Methods with a Standardized Proficiency Panel

BACKGROUND

The most frequent infectious complication in transfusion therapy in developed countries is related to the bacterial contamination of platelet concentrates (PCs). Rapid and cultural screening methods for bacterial detection in platelets are available, but external performance evaluation, especially of rapid methods, has been difficult to realize so far. Here we summarize the results of three individual collaborative trials using an external quality assessment program (EQAP) for the application of current rapid and cultural screening methods.

METHODS

Three different modules were available for the detection of bacterial contamination: module 1: rapid methods, module 2: culture methods, module 3: bacterial identification methods. The sample set-up included up to six different bacterial strains, 1-2 negative samples and 4-6 positive samples with stabilized bacterial cell counts (approximately 10(3)/10(4)/10(5) CFU/ml). Time schedule for testing was limited (module 1: 6 h, module 2 and 3: 7 days).

RESULTS

Samples of module 1 were analyzed with two different rapid methods (BactiFlow, NAT). The results of the three individual collaborative trials showed that all participants detected the negative samples with both assays correctly. Samples spiked with 10(4) to 10(5) CFU/ml of bacteria obtained positive results with both rapid screening methods, whereas samples spiked with only 10(3) CFU/ml disclosed a lower number of correctly identified positive results by NAT (86.6-93.8% sensitivity) compared to BactiFlow (100% sensitivity). The results for modules 2 and 3 revealed a 100% diagnostic sensitivity and specificity in all three collaborative trials.

CONCLUSION

This proficiency panel facilitates the verification of the analytical sensitivity of rapid and cultural bacterial detection systems under controlled routine conditions. The concept of samples provided in this EQAP has three main advantages: i) samples can be examined by both rapid and culture methods, ii) the provided material is matrix-equivalent, and iii) the sample material is ready-to-use.

Propagation capacity of bacterial contaminants in platelet concentrates using a luciferase reporter system

INTRODUCTION

Currently the use of molecular tools and techniques of Genetic Engineering in the study of microbial behavior in blood components has replaced the employment of classical methods of microbiology. This work focuses on the use of a novel lux reporter system for monitoring the contaminating propagation capacity of bacteria present in platelet concentrates under standard storage conditions in the blood bank.

METHODS

A miniTn5 promotor probe carrying the lux operon from Photorhabdus luminiscens (pUTminiTn5luxCDABEKm2) was used to construct four bacterial bioluminescent mutants: Escherichia coli, Salmonella typhi, Proteus mirabilis and Pseudomonas aeruginosa. Luminescent mutants were used for contamination tests with 20 CFU in platelet concentrates bags and were stored under standard storage conditions in the blood bank (100 rpm at 22 °C). The measurements of luminous activity and optical density were used to monitor bacterial proliferation during 7 days (168 h).

RESULTS

During the exponential growth phase (log) of bacterial strains, a lineal correlation between luminous activity vs biomass was observed (R(2) = 0.985, 0.976, 0.981) for E. coli::Tn5luxCDABEKm2, P. mirabilis::Tn5luxCDABEKm2 and P. auriginosa::Tn5luxCDABEKm2, respectively. The above indicates that metabolic activity (production of ATP) is directly related to biomass in this phase of microbial growth. While conducting experiments, the inability to propagate S. typhi::Tn5luxCDABEKm2 was detected. We can speculate that platelet concentrates contain specific components that prevent the propagation of S. typhi.

CONCLUSION

The use of luxCDABE system for the quantification of luminous activity is a rapid and sensitive alternative to study the propagation and auto-sterilization of bacterial contaminants in platelet concentrates.