The development of antibiotic resistances in common pathogens is an increasing challenge for therapy of infections and especially severe complications like sepsis. To prevent administration of broad-spectrum and potentially non-effective antibiotics, the susceptibility spectrum of the pathogens underlying the infection has to be determined. Current phenotypic standard methods for antibiotic susceptibility testing (AST) require the isolation of pathogens from the patient and the subsequent culturing in the presence of antibiotics leading to results only after a delay of 24-72 h. Since the early initialization of an effective antibiotic therapy is crucial for patients outcome in severe infections, faster methods of AST are urgently needed. A huge number of different assay systems is currently tested for their practicability for fast detection of antibiotic resistance profiles. They can be divided into genotypic ones which detect the presence of certain genes or gene products associated with resistances, and phenotypic assays which determine the effect of antibiotics on the pathogens. In this minireview we summarize current developments in fast phenotypic tests that use photonic approaches and critically discuss their current status and steps that are still required to bring these assays into clinical practice.