Use of a fluidic device

A method of determining a response of a microorganism to a test substance, said method comprising:

• providing a culture of said microorganism in a three-dimensional, 3D, culture matrix arranged in a culture chamber of a fluidic device having a first fluid channel flanking a first end portion of said culture chamber and a second fluid channel flanking a second, different end portion of said culture chamber;
• connecting an input of said first fluid channel to a first fluid flow comprising said test substance at a first concentration;
• connecting an input of said second fluid channel to a second fluid flow lacking said test substance or comprising said test substance at a second concentration that is lower than said first concentration to form a concentration gradient of said test substance over at least a portion of said 3D culture matrix;
• and
• determining a response of said microorganism to said test substance based on a position, relative to said first end portion and/or said second, different end portion, of any border zone in said 3D culture matrix between a first response zone in which said microorganism shows a first response to said test substance and a second response zone in which said microorganism shows a second, different response to said test substance.

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

• a fluidic device comprising:
• a culture chamber configured to house a culture of said microorganism in a three-dimensional, 3D, culture matrix;
• a first fluid channel flanking a first end portion of said culture chamber;
• and
• a second fluid channel flanking a second, different end portion of said culture chamber;
• a first fluid reservoir comprising a first fluid comprising said test substance at a first concentration, said first fluid reservoir is configured to be connected to an input of said first fluid channel;
• a second fluid reservoir comprising a second fluid lacking said test substance or comprising said test substance at a second concentration that is lower than said first concentration, said second fluid reservoir is configured to be connected to an input of said second fluid channel to form a concentration gradient of said test substance over at least a portion of said 3D culture matrix;
• and
• a computer-based system configured to i) take at least one image of said 3D culture matrix, ii) process said at least one image to identify a position, relative to said first end portion and/or said second, different end portion, of any border zone in said 3D culture matrix between a first response zone in which said microorganism shows a first response to said test substance and a second response zone in which said microorganism shows a second, different response to said test substance, and ii) determine a response of said microorganism to said test substance based on said position of said any border zone.