The present invention relates to a novel bioactivity testing structure for single cell tracking using a gelling agent and a bioactivity testing system including the testing structure. The present invention also relates to bioactivity testing, drug susceptibility testing, antibiotic screening, and diagnostic methods using the testing structure. The bioactivity testing structure of the present invention enables very rapid and simple drug susceptibility testing of bacteria, particularly Mycobacterium tuberculosis, drug screening, and bacterial diagnosis. Particularly, the use of the testing structure enables DST and diagnosis of bacteria only by pretreatment without the need to concentrate human sputum samples irrespective of inoculum effect, ensuring rapid, accurate, and simple testing compared to conventional tuberculosis diagnosis or DST systems. In addition, the testing structure of the present invention simultaneously enables the diagnosis and drug susceptibility testing of tuberculosis. Therefore, the present invention provides an effective alternative to the prior art.