Which organism is most commonly responsible for urinary tract infections in pregnant women?

Escherichia coli is the organism most commonly responsible for urinary tract infections (UTIs) in pregnant women. This is largely due to its prevalence in the gastrointestinal tract, where it is a normal inhabitant. The anatomical and physiological changes that occur during pregnancy, such as hormonal changes that cause urinary stasis, can increase the risk of infections.

E. coli is known for its ability to adhere to the uroepithelial cells and its virulence factors, making it particularly adept at colonizing the urinary tract. This means it can easily establish an infection, which is why it is the predominant pathogen in UTI cases among pregnant women.

Other organisms like Klebsiella pneumoniae and Proteus can also cause UTIs, but they are less frequently the causative agents compared to E. coli. Additionally, while gram-positive cocci can also be involved in urinary infections, especially in certain genitourinary conditions, they are not as commonly implicated as E. coli in the context of pregnant women.