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Proteeae Infections

By Larry M. Bush, MD, Affiliate Professor of Clinical Biomedical Sciences; Affiliate Associate Professor of Medicine, Charles E. Schmidt College of Medicine, Florida Atlantic University; University of Miami-Miller School of Medicine ; Maria T. Perez, MD, Associate Pathologist, Department of Pathology and Laboratory Medicine, Wellington Regional Medical Center, West Palm Beach

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The Proteeae are normal fecal flora that often cause infection in patients whose normal flora have been disturbed by antibiotic therapy.

The Proteeae constitute at least 3 genera of gram-negative organisms:

  • Proteus: P. mirabilis, P. vulgaris, and P. myxofaciens

  • Morganella: M. morganii

  • Providencia: P. rettgeri, P. alcalifaciens, and P. stuartii

However, P. mirabilis causes most human infections. These organisms are normal fecal flora and are present in soil and water. They are often present in superficial wounds, draining ears, and sputum, particularly in patients whose normal flora has been eradicated by antibiotic therapy. They may cause bacteremia and deep-seated infections, particularly in the ears and mastoid sinuses, peritoneal cavity, and urinary tract of patients with chronic UTIs or with renal or bladder stones; Proteus organisms produce urease, which hydrolyzes urea, leading to alkaline urine and the formation of struvite (magnesium ammonium phosphate) stones.

P. mirabilis is often sensitive to ampicillin, carbenicillin, ticarcillin, piperacillin, cephalosporins, fluoroquinolones, and aminoglycosides and resistant to tetracyclines. Multidrug-resistant P. mirabilis is an emerging problem.

Indole-positive species (P. vulgaris, M. morganii, P. rettgeri) tend to be more resistant but generally are sensitive to fluoroquinolones, carbapenems, piperacillin/tazobactam, 3rd-generation cephalosporins, and cefixime.