SDHB and bacterial urinary tract infection: To confirm that the fitness advantage of the sdhBfrdA double mutant strain was due to the loss of FRD, the frdABCD operon was expressed in the sdhBfrdA double mutant strain and the fitness advantage was lost and, moreover, complementation produced a fitness defect during UTI in the bladder and kidneys (P = 0.002 and P = 0.0117, respectively) (Fig 3D) reminiscent of the fitness defect observed in the sdhB single mutant.