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A 3D-printed device for reproducible imaging of 96-well broth microdilution plates

K Dewaele(1) L Hardy(1) B C de Jong(1) L Rigouts(1,2)

1:Institute of Tropical Medicine Antwerp; 2:University of Antwerp

Broth microdilution (BMD) assays are gaining entrance for drug-susceptibility testing in Mycobacterium tuberculosis. Interpretation of these assays has limited reproducibility between observers, especially for ambiguous phenotypes (e.g. pinpoint growth). To support reproducible MIC determination, we created a 3D-printed photographic device with a tray for generic 96-well plates. It houses a single-board Linux computer, two cameras (one for each plate halve), and light sources for tangential and trans-illumination. We developed a graphical user interface for image acquisition and minimal inhibitory concentration determination (MIC). Compared to the Thermo Fisher Vizion, a proprietary system for read-out of Sensititre BMD assays, our device has several assets. It has a four times higher pixel density, allowing differentiation of smaller colony features. It provides both darkfield and brightfield images in a single acquisition cycle, while Vizion is limited to either of both. Using a semi-transparent mirror, our device enables manual plate inspection in addition to imaging, both in standardised lighting conditions. At 400 euros, our device costs a fraction of the price of Vizion. Compared to Vizion, our device suffers more from perspective artifacts in U-bottom plates with a limited volume (50 µL), and from lid condensation artifacts. Our device’s performance is yet to be compared to the BIOMIC V3 (Giles Scientific), another recently introduced commercial plate imager. A comparative study of MIC accuracy and reproducibility, using manual plate read-out as a reference, is ongoing. Future iterations of this device will focus on improving perspective and lighting artifacts, as well as implementing automated MIC determination algorithms.

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