The emergence and spread of multidrug resistant bacteria is a global threat to human health. The problem is aggravated as a result of unnecessary and incorrect use of broad-spectrum antibiotics. One way to assure correct antibiotic use and reduce the development of antibiotic resistance is to assay the susceptibility profile of the infection before treatment is initiated. However, the current methods for Antibiotics Susceptibility Testing (AST) are too slow to be used for routine screening. Here we present a fast AST test, FASTest, that captures bacterial cells in individual nanofluidics channels and monitor their response to different antibiotics based on direct imaging. By averaging the growth rate over a few hundred cells we can determine the susceptibility to several antibiotics in less than 30 min even at cell densities as low as 104 CFU/mL of sample. This is a time scale and concentration that makes the FASTest practically useful for guiding the primary antibiotic treatment of several types of infections.