Which bacteria is primarily responsible for causing pyelonephritis?

Pyelonephritis, which is an infection of the kidney, is primarily caused by Escherichia coli (E. coli). This bacterium is part of the normal flora of the gastrointestinal tract, but certain strains can ascend from the bladder into the kidneys, leading to pyelonephritis. This condition is characterized by symptoms such as fever, flank pain, and dysuria, and it often occurs due to a urinary tract infection (UTI) that is not adequately treated.

E. coli’s virulence factors, such as fimbriae, facilitate its adherence to the uroepithelium, which can lead to infection and inflammation of the renal parenchyma. Understanding the role of E. coli in pyelonephritis is essential for effective diagnosis and treatment, as antibiotics commonly target this bacterium specifically in clinical practice.

The other options, while associated with various infections, do not have the same strong link to pyelonephritis as E. coli does. Therefore, this makes E. coli the correct and most relevant choice in the context of causing pyelonephritis.