Metabolic Regulation of Quiescence and Antibiotic Tolerance in Uropathogenic Escherichia coli.

Urinary tract infections (UTIs) pose a global public health threat. Uropathogenic Escherichia coli (UPEC) cause the majority of UTIs and a quarter of infections are recurrent within six months. This may be attributed to UPEC entering a non-proliferative, or quiescent state that allows some cell populations to evade the host immune response and survive exposure to antibiotics, thus causing reinfection upon cessation of antibiotic treatment. A significant proportion of UPEC isolates, including the classic endemic UPEC lineage CFT073, are unable to proliferate at low cell density in vitro with glucose as the sole carbon source, but proliferate robustly at high cell density. Quiescence at low cell density is inhibited by external cues, such as peptidoglycan fragments, L-Lysine, L-Methionine, and succinate, which induce proliferation of quiescent cells and lead to a rapid increase in cell number. Here, we show that quiescent CFT073 cells are tolerant to antibiotics in vitro; however, proliferative cells are susceptible to antibiotics. Furthermore, we show that succinate fails to induce proliferation of cells deleted for sucCD, which encode enzymes that interconvert succinate and succinyl-CoA in the tricarboxylic acid cycle. This suggests that succinyl-CoA is limiting in the cell during quiescence and that quiescent cells may have lower metabolic activity. We demonstrate that increased levels of SucAB, which synthesize succinyl-CoA from alpha ketoglutarate, prevent quiescence and induce proliferation. These results are consistent with a model in which quiescent UPEC cells exhibit reduced metabolism with limited succinyl-CoA, and this underlies the antibiotic tolerance exhibited during UPEC quiescence in vitro.