A nurse is caring for a 3-year-old client who has been diagnosed with acute cystitis and is prescribed cephalexin. Which of the following pathogens should the nurse identity as the most common bacterial cause of UTIs?

A. Escherichia coli: E. coli is the most common bacterial pathogen responsible for urinary tract infections in children and adults. It originates from the gastrointestinal tract and can colonize the urethra, ascending to the bladder and causing cystitis. Understanding this helps guide appropriate antibiotic selection, such as cephalexin. B. Klebsiella: Klebsiella species can cause UTIs but are less common than E. coli, typically occurring in children with structural abnormalities of the urinary tract or those with frequent hospitalizations. C. Enterococcus: Enterococcus can be a cause of UTIs, especially in hospitalized patients or those with catheterization, but it is not the primary pathogen in otherwise healthy children with acute cystitis. D. Pseudomonas aeruginosa: Pseudomonas is an uncommon cause of UTIs in healthy pediatric clients. It is more often associated with complicated UTIs or immunocompromised patients.