Escherichia coli is the most common cause of urinary tract infections (UTIs) in pregnancy due to its presence as a predominant facultative anaerobic gram-negative rod in the gastrointestinal tract. The proximity of the anus to the urethra facilitates ascending infection. During pregnancy, physiological changes like urinary stasis and decreased ureteral peristalsis increase susceptibility to E. coli colonization. Additionally, pregnancy-induced immunological changes impair the host’s ability to clear these bacteria effectively. The ability of E. coli to adhere to uroepithelial cells via fimbriae promotes colonization and persistent infection. Understanding this pathophysiology is crucial for targeted antibiotic therapy and preventing complications such as pyelonephritis.

Reference: Harrison’s Principles of Internal Medicine, Jameson et al., 20th Edition.