Fitness Cost and Compensatory Evolution in Levofloxacin-Resistant Mycobacterium aurum.

We isolated spontaneous levofloxacin-resistant strains of Mycobacterium aurum to study the fitness cost and compensatory evolution of fluoroquinolone resistance in mycobacteria. Five of six mutant strains with substantial growth defects showed restored fitness after being serially passaged for 18 growth cycles, along with increased cellular ATP level. Whole genome sequencing identified putative compensatory mutations in glgC gene which restored the fitness of the resistant strains, presumably by altering the bacterial energy metabolism.