Final answer:
The causative agent most likely associated with acute pyelonephritis with bacteremic spread from a distant location, particularly in the case of a hospital-acquired infection that is resistant to antibiotics like carbapenems, is Klebsiella pneumoniae.
Step-by-step explanation:
The causative agent associated with acute pyelonephritis that spreads bacteremically from a distant location can be several types of bacteria. In the scenario where the infection is hospital-acquired, as indicated by recent surgery, and is resistant to commonly used antibiotics including carbapenems, the most relevant pathogen known to cause this condition would be Klebsiella pneumoniae. Gram-negative bacteria such as Escherichia coli are the most common cause of urinary tract infections; however, the case pointing towards a post-surgical, hospital-acquired infection resistant to multiple drugs, including carbapenems, aligns with the profile of Klebsiella pneumoniae. This bacterium is an opportunistic, capsulated, gram-negative rod known for causing infections in the urinary tract that can become severe and resistant to treatment, as documented in similar clinical cases.