Novel system rapidly detects low levels of bacteria in blood [PreClinical]

1. The Integrated Comprehensive Droplet Digital Detection (IC 3D) system combined three distinct technologies to detect down to single-cell levels of blood bacterial infection.

2. Within 4 hours, the IC 3D provided quantitative measurements of infection level with high sensitivity and specificity.

Evidence Rating Level: 2 (Good)

Study Rundown: Bacterial infection of the blood can lead to sepsis, a severe body-wide immune response with high mortality rates. Early diagnosis of infection is key to effective treatment and improved patient survival rates. This proof-of-concept study demonstrated the ability of the IC 3D to rapidly detect specific types of bacteria in the blood at low levels. The IC 3D employed DNA-based probes called DNAzymes to detect bacteria; furthermore, the analyzed blood was separated into droplets, which allowed the reaction between DNAzymes and a bacterium in an individual droplet to quickly occur. In clinical blood samples, the IC 3D identified the target E. coli bacteria and not other bacteria strains or normal blood components. The IC 3D system confirmed the presence or absence of target bacteria within an hour, and longer analysis times yielded quantitative measurements of bacteria numbers. These measurements were accurate across a wide range of bacteria levels, down to single-digit numbers of bacteria cells in the blood samples.

The detection system developed in this study had a number of strengths when compared to current detection technologies. In addition to short analysis times and a low limit of detection, the IC 3D measured bacteria in blood without requiring sample preprocessing. The current system design is limited by its ability to detect only one type of bacteria (e.g. E. coli) per analysis. The researchers behind the IC 3D are currently developing a multiple-wavelength detection system that would allow for simultaneous analysis of multiple bacteria types, which should aid in clinically relevant, broad diagnoses. With further development, the IC 3D should provide early detection of bacterial infection in the blood and improve patient outcomes.

Click to read the study in Nature Communications

Relevant Reading: Fluorogenic DNAzyme Probes as Bacterial Indicators

In-Depth [in vitro study]: Three technologies comprised the IC 3D system. First, the underlying molecular reaction for E. coli detection was based on DNAzyme sensors. DNAzymes were designed to specifically target E. coli and emit fluorescence upon binding with bacterial cell components. Second, a microfluidic device was used to separate and dilute the blood sample into millions of droplets containing blood + DNAzymes + bacteria lysis buffer that were suspended in an oil carrier fluid. The speed of the DNAzyme reaction was increased when enzymes and bacteria were contained within the picoliter-sized droplets. Third, a three-dimensional particle counter was used to rapidly identify fluorescent droplets.

Blood samples spiked with E. coli in the range of 1 to 10,000 bacterial cells per milliliter were tested with the IC 3D. The number of detected cells closely matched the original number of spiked cells. These samples were compared to clinical isolates of various non-E. coli bacterial strains in a single-blinded experiment, yielding a false-positive rate of zero and a false negative rate of 0.5%. In blood samples with 1 bacterial cell per milliliter, the IC 3D detected a mean reading of 0.77 cells. Across the full range of bacterial concentrations tested, a binary result confirming the presence or absence of bacteria was produced in approximately 45 minutes, and full quantification of bacteria cell numbers was completed within 4 hours.

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