AEMCA Practice Exam

What is the most common bacterial cause of a urinary tract infection?

1. Staphylococcus aureus

2. Escherichia coli

3. Streptococcus pneumoniae

4. Proteus mirabilis

The correct answer is: Escherichia coli

Escherichia coli (E. coli) is recognized as the most common bacterial cause of urinary tract infections (UTIs). This organism is a normal inhabitant of the gastrointestinal tract, which can enter the urinary system typically due to poor hygiene or anatomical factors. About 80-90% of uncomplicated UTIs are caused by E. coli. Its ability to adhere to the uroepithelial cells enhances its virulence, allowing it to colonize and multiply within the urinary tract. While the other bacteria listed can cause UTIs, they are not as prevalent as E. coli. Staphylococcus aureus and Streptococcus pneumoniae are more often associated with skin infections and respiratory infections, respectively, rather than being primary causes of UTIs. Proteus mirabilis can cause UTIs, especially in patients with long-term urinary catheters or structural abnormalities but is significantly less common than E. coli in general community-acquired urinary tract infections. Thus, the prevalence and pathogenicity of E. coli make it the leading bacterial culprit in urinary tract infections.