Infections, particularly those due to drug-resistant pathogens, significantly increase morbidity and mortality as well as cost of treatment and length of hospital stays. Staphylococcus aureus, a highly human-adapted organism, is the most common pathogen causing nosocomial infections. Among S. aureus, especially methicillin-resistant S. aureus (MRSA) causes problems in therapy and infection control. Understanding the mechanisms of infections is as important as the development of rapid tools for diagnosis. Within the Photonics4Life project "From Infection to Detection" these two goals are addressed. Modern optical technologies, such as multi-focus quantitative digital holographic microscopy (DHM) phase contrast, holographic optical tweezers (HOT) and Raman spectroscopy have been employed to analyse the cell morphology, cell dynamics and cellular refractive index of endothelial cells before and after incubation with S. aureus (or with model bacteria for HOT and DHM analysis). Individual bacteria inside the cells have been visualized and defined infection scenarios at the single cell level could be created. Finally, optical techniques were evaluated for further sub-typing of S. aureus strains and compared to the established spa typing method.