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With the rise of antibiotic resistance, phage therapy is seen as a promising alternative to cure infection to multiresistant bacteria strains. However, phage susceptibility tests currently carried out are time-consuming and are not compliant with the automated environment of hospital laboratories. In this work, we present a method for phage susceptibility testing through optical density measurement with the use of a lensless imaging technique. Fluid assays containing bacteria and phages are loaded in the wells of a 5mm-thick custom-made microfluidic card. The card is put on a 3.3 cm2 CMOS imaging sensor taken from a CANON dslr camera. It is illuminated by a screen paired with a 560 nm spectral filter to provide a homogeneous monochromatic lighting over the whole sensor area. Thanks to the large imaging area of the CMOS sensor, it is possible to simultaneously monitor the level of light transmitted through the well of the microfluidic card and hence to compute the optical density of a dozen sample without the need of mechanical elements. We thus monitor the decay or increase of optical density to determine respectively the lysis or growth of the bacteria under test. This method provides a reliable result of optical phage susceptibility testing in less than 4 hours. The prototype shown here is compact, inexpensive (<1 k€) and is compliant with automated environment of hospital laboratories. Moreover, it is versatile and can be used for other application such as lysis plaque imaging to provide a fast measurement of a viral titer of a bacteriophage suspension.
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