P79

Tuberculosis remains a highly prevalent disease and a significant contributor to worldwide mortality. The fight against TB requires surveillance of the population of the strains circulating worldwide. Currently, there is little knowledge of the characteristics of M. tuberculosis that cause it to be involved in outbreaks.This study aimed to answer if the relative fitness of M. tuberculosis strains might affect tuberculosis transmission. We identified six pairs of high- and low-transmission M. tuberculosis strains and transformed them with selective plasmids. Two bacterial strains, each representative of high- and low-transmission groups, were placed in one culture in a 1:1 ratio of colony-forming units. Culture samples were plated on selective media on days 0 and 7 to assess the ratio of colony-forming units. Next, the strains' relative competitive fitness (W) was calculated. The median relative fitness of high-transmission to low-transmission strains of M. tuberculosis was -0.23 (IQR -1.47-0.32). These results suggest that bacterial fitness might not be associated with increased tuberculosis transmission. Our results require further confirmation with a larger sample of M. tuberculosis strains.