Which organism causes most urinary tract infections (UTIs)?

Choice A rationale Pseudomonas aeruginosa is a gram negative rod that often causes healthcare associated infections, particularly in patients with indwelling catheters or those who are immunocompromised. While it is a significant pathogen in complex urinary tract infections, it is not the most common cause in the general population. It is known for its antibiotic resistance and biofilm formation, making it difficult to treat. However, its prevalence is much lower than other enteric bacteria in simple community acquired cases. Choice B rationale Escherichia coli is part of the normal flora of the gastrointestinal tract and is responsible for approximately 80 percent to 90 percent of community acquired urinary tract infections. Its proximity to the urethra allows for easy migration and colonization of the urinary tract. This organism possesses specific virulence factors, such as fimbriae, which allow it to adhere strongly to the bladder wall epithelium. This adherence prevents the bacteria from being washed away during urination, leading to localized infection. Choice C rationale Klebsiella pneumoniae is another gram negative bacterium found in the intestinal tract that can cause urinary tract infections, especially in hospital settings. It is often associated with more complicated cases or infections in patients with underlying health conditions like diabetes. While it is a common uropathogen, its frequency does not match that of Escherichia coli. Klebsiella infections are concerning due to the increasing prevalence of multidrug resistant strains, such as those producing carbapenemase, which complicate standard treatment. Choice D rationale Proteus mirabilis is frequently associated with urinary tract infections in patients with long term urinary catheters or structural abnormalities of the urinary tract. It produces urease, an enzyme that increases urine pH and can lead to the formation of struvite kidney stones. Although it is a well known cause of persistent and complicated infections, it remains less common than Escherichia coli. Its ability to swarm across surfaces allows it to migrate up catheters, but it remains a secondary cause.