Use of a fluidic device

A system for determining a response of a microorganism to a test substance, the system comprising:

• a fluidic device comprising:
• a culture chamber configured to house a culture of the microorganism in a three dimensional (3D) culture matrix;
• a first fluid channel flanking a first end portion of the culture chamber;
• and
• a second fluid channel flanking a second, different end portion of the culture chamber;
• a first fluid reservoir comprising a first fluid comprising the test substance at a first concentration, the first fluid reservoir is configured to be connected to an input of the first fluid channel;
• a second fluid reservoir comprising a second fluid lacking the test substance or comprising the test substance at a second concentration that is lower than the first concentration, the second fluid reservoir is configured to be connected to an input of the second fluid channel to form a concentration gradient of the test substance over at least a portion of the 3D culture matrix;
• and
• a computer-based system configured to i) take at least one image of the 3D culture matrix, ii) process the at least one image to identify a position, relative to the first end portion and/or the second, different end portion, of any border zone in the 3D culture matrix between a growth zone of growing microorganism and a non-growth zone lacking growth of the microorganism, wherein the growth of the microorganism in the growth zone is not inhibited by the test substance, iii) process the at least one image to identify a width of the any border zone, iv) determine a minimal inhibitory concentration (MIC) of the microorganism to the test substance based on the position of the any border zone by correlating the position to a concentration or a concentration range of the test substance based on gradient information defining concentration versus position in the 3D culture matrix for the concentration gradient, and v) determine a resistance of the microorganism to the test substance based on the width of the any border zone.