Which microorganisms are commonly isolated in acute pyelonephritis (kidney infection)?

Updated: Jul 01, 2021
  • Author: Tibor Fulop, MD, PhD, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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As noted above, UPEC account for most uncomplicated pyelonephritis cases and a significant portion of complicated pyelonephritis cases. The following microorganisms are also commonly isolated:

  • Staphylococcus saprophyticus
  • Klebsiella pneumoniae
  • Proteus mirabilis
  • Enterococci
  • S aureus
  • Pseudomonas aeruginosa
  • Enterobacter species

This is the same spectrum of organisms cultured in cystitis. In 10-15% of symptomatic cystitis cases, cultures using routine methods remain negative, although the symptoms typically respond to antibiotic therapy. In some cases, cultures using selective media have grown Gardnerella vaginalis, Mycoplasma hominis, and Ureaplasma urealyticum. These data cannot be extended to acute pyelonephritis, but they do illustrate the difficulties in isolating the causative organism.

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