Which organism is the most common cause of urinary tract infection?

Which organism is the most common cause of urinary tract infection?

• A. Staphylococcus aureus
• B. Escherichia coli
• C. Pseudomonas aeruginosa
• D. Klebsiella pneumoniae

Answer: (B)

In urinary tract infections, the most frequent pathogen is a gut bacterium that ascends into the urinary tract. Escherichia coli, particularly uropathogenic strains with adhesins that help them attach to the bladder lining, is by far the most common cause. Its ability to colonize the periurethral region, adhere to uroepithelium, and ascend into the bladder explains why it leads to cystitis and can progress to upper tract infection. E. coli accounts for the majority of community-acquired UTIs, estimated around 70–80%. The other organisms listed—Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae—can cause UTIs but are much less common overall, often associated with specific settings like hospitalization, catheter use, or particular risk factors rather than representing the leading cause.

In urinary tract infections, the most frequent pathogen is a gut bacterium that ascends into the urinary tract. Escherichia coli, particularly uropathogenic strains with adhesins that help them attach to the bladder lining, is by far the most common cause. Its ability to colonize the periurethral region, adhere to uroepithelium, and ascend into the bladder explains why it leads to cystitis and can progress to upper tract infection. E. coli accounts for the majority of community-acquired UTIs, estimated around 70–80%. The other organisms listed—Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae—can cause UTIs but are much less common overall, often associated with specific settings like hospitalization, catheter use, or particular risk factors rather than representing the leading cause.