Final answer:
The most common organism causing bladder infections is the bacterium Escherichia coli (E. coli), which is typically treated with antibiotics.
Step-by-step explanation:
The organism most commonly responsible for bladder infections is a type of bacteria called Escherichia coli (E. coli). These infections, which are a type of urinary tract infection (UTI), are significantly more common in females due to anatomical differences, such as the shorter urethra and its proximity to the anus which facilitates the transfer of bacteria from the GI tract to the bladder. Gram-negative bacteria like E. coli are the most typical culprits, although other bacteria can also be responsible. UTIs, and thus bladder infections, are treated with antibiotics.