GLUL and bacterial urinary tract infection: Three mutants pertaining to Category 2 were used for validation: glutamine synthetase (glnA, ~3-fold defect in bladder and kidney colonization), the bifunctional polymyxin resistance protein previously identified by STM in the ascending UTI model (arnA, ~3-fold defect), and phospholipase A (pldA, ~2-fold defect).