Which of the following bacteria is commonly associated with UTIs?

Escherichia coli is the most common bacterium associated with urinary tract infections (UTIs). E. coli is part of the normal flora of the gastrointestinal tract, but it can cause infections when it enters the urinary system. This bacterium has specific virulence factors, such as adhesins that enable it to adhere to the uroepithelium and evade the host's immune response, making it particularly adept at causing UTIs.

The other bacteria listed are associated with different types of infections or conditions. For example, Streptococcus pneumoniae is primarily known for causing respiratory infections such as pneumonia and meningitis. Clostridium difficile is associated with antibiotic-associated diarrhea and colitis. Mycobacterium tuberculosis is the causative agent of tuberculosis, primarily affecting the lungs but also capable of causing extrapulmonary infections. Therefore, E. coli stands out as the predominant pathogen related to UTIs due to its prevalence and specific adaptations for infecting the urinary tract.