Abstract Background A strategic way to gain a deeper understanding of how infection occurs is to characterize the mechanisms of pathogen binding and uptake. To accomplish this, we have focused our efforts on developing approaches that enable real-time monitoring of the initial stages of pathogen binding and the dynamics of the corresponding cellular response, including how membrane receptors are recruited to the binding sites. Past efforts have relied largely on widefield fluorescence imaging to track receptor recruitment and pathogen uptake. Methods In this work, we have applied holotomography (HT) to probe pathogen binding using 3D refractive index (RI) reconstruction and spatial–temporal bacteria tracking. While promising, we also report on the challenges encountered in developing a multimodal correlative HT-fluorescence approach for real-time visualization of pathogen uptake and engagement. Results We report here on an imaging platform that integrates HT with multicolor fluorescence microscopy. The system can reconstruct quantitative RI volumes and perform single particle and pathogen tracking. We applied this system to monitor the interaction of Neisseria gonorrhoeae bacteria with live CEACAM-expressing HeLa cells, coupling HT with simultaneous two-channel highly inclined laminated optical sheet (HILO) fluorescence imaging to track the dynamics and spatial distribution of membrane receptors and bacteria within the same field of view. Simultaneous acquisition and co-registration of the phase and fluorescence channels resulted in a multicolor, temporally synchronized dataset of pathogen binding and receptor engagement, portending video-rate three-dimensional tracking of pathogen binding and uptake. Conclusions The coupled platform we have developed has enabled direct volumetric imaging of the dynamics of pathogen binding and concomitant recruitment of membrane receptors on live cells. The platform closes a critical gap between optically sectioned fluorescence and label-free 3D phase imaging and can be adapted to other receptor–ligand systems that would benefit from correlated structural and functional insights.
Yu et al. (Thu,) studied this question.