Some bacteriophages or phages (viruses that infect bacteria) are capable of destroying antibiotic-resistant bacteria and are consequently used in therapy (phagotherapy). Originally, they were administered as standardized cocktails of several phages, sometimes up to 12 or 15. This method has been abandoned due to the risk of developing resistance. Instead, treatment is now tailored to the individual patient. The bacterium responsible for the infection is collected and a technician observes, in a culture medium, which phages are active against it. The whole process takes 16 to 24 hours. Occasionally, a phage is erroneously considered inactive if the bacterial debris (lysis plaques) is too small.

The new lensless imaging technique developed by the researchers overcomes these drawbacks. It can locate lysis plaques of any size and count them to determine the "infectious titer of the phage", i.e. the equivalent of the concentration for an antibiotic. During tests conducted by the Irig-Leti research collaboration at the Lausanne University Hospital in Switzerland, the activity of anti-Staphylococcus aureus phages could be determined in three hours, and their infectious titer was determined in just over eight hours.

The lysis plaques are observed using a lensless imaging system with a large area (24 x 36 mm²). It incorporates an algorithm for identifying the optical signature of the lysis plaques and for counting them.

The researchers at the Irig, the CEA-Leti, the Laboratoire des Technologies de la Microélectronique (CNRS) and the Lausanne University Hospital are continuing this work by developing, with the Hospices Civils de Lyon and the support of the ANR, a proof-of-concept demonstrator that will include (among other things) an interface usable by biologists.