Photophysical characterization and fluorescence imaging of Helicobacter pylori endogenous porphyrins

Helicobacter pylori (Hp) is among the most common infective agents in humans and is responsible for several gastric infections; moreover, its antibiotic resistance is raising new challenges. Antimicrobial photodynamic therapy (PDT) is a promising technique based on the use of non-toxic photosensitizers that, under the effect of a selected visible light, can generate cytotoxic reactive oxygen species; PDT is particularly effective when the target microorganism presents endogenous photosensitizers. It has been shown that the photosensitizers protoporphyrin IX and coproporphyrin I are endogenously produced in Hp, making it a suitable target for PDT. Aiming at the production of an ingestible LED-based robotic pill for intragastric PDT able to perform in situ irradiation without the use of endoscopic devices, the effectiveness of Hp photokilling in models has to be determined. We studied the distribution of porphyrins within bacteria suspensions and biofilms and adapted a protocol for porphyrins extraction from bacteria to characterize the spectroscopic features of the extracts. Project: "CapsuLight - Design of an ingestible robotic pill based on LED sources for the treatment of gastrointestinal disorders" (CUP B52I14005760002) financed by Regione Toscana Bando FAS Salute 2014 (Italy). P-809 Biomechanical studies with ultrasound in cell biology V. Bentivegna1, F. Stewart1, S. Cochran2, I. N¨athke1 1Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, UK; 2School of Engineering, University of Glasgow, Glasgow, UK During tissue development and cancer progression, cells undergo mechanical changes and respond differently to physical cues from their environment. Usually measuring physical properties of biological samples relies on direct physical contact with the sample. We propose ultrasound as a versatile tool for imaging and also exerting forces on cells that does not require direct contact. Using a 40 MHz microultrasound transducer, we compared radiofrequency signals with optical images of 3D tissue structures. This revealed that the size of spherical structures correlates with the ultrasound RF signal. Ultrasound overestimates the size of hollow cysts by 33%, while no such offset was observed in solid spheroids. Early results also suggest that microultrasound can reveal mechanical properties. At lower frequencies (~ 4 MHz) and higher intensities, ultrasound can compress cell layers via acoustic radiation pressure and without the need to directly contact the sample. This allowed investigating how cells react to external mechanical forces. Developing this approach further will permit comparison of mechanical properties of tissue at different stages of cancer progression and increase our understanding of how mechanical forces direct