Genera Proteus, Providencia & Morganella
These three genera belong to the Enterobacteriaceae family and are part of the PPM group of opportunistic pathogens.
General Characteristics
- Gram-negative rods
- Facultative anaerobes, oxidase-negative, catalase-positive
- Non-spore forming, motile (except Morganella, which is weakly motile)
- Urease positive (important for diagnosis, especially for Proteus)
- Lactose non-fermenters (colorless on MacConkey agar)
- Found in intestinal tract of humans and animals — opportunistic pathogens
- Often involved in nosocomial (hospital-acquired) infections, especially in immunocompromised patients
- Phenylalanine deaminase positive (all 3) → unique to PPM group
Proteus (mainly P. mirabilis and P. vulgaris)
Morphology & Colony Appearance
- Swarming motility → Concentric ring colonies on agar
- H2S production → black precipitate in media like TSI
- Characteristic fishy odor
Pathogenesis
- Urease enzyme splits urea into ammonia and CO₂ → alkalizes urine → predisposes to struvite stones (kidney stones)
- Increases pH → promotes crystallization of ions
- Can adhere to uroepithelium and invade tissues
Virulence Factors of Proteus:
Diseases Caused by Proteus
- Urinary Tract Infections (UTIs) — most common diseaae.
- Pyelonephritis
- Wound infections (especially in burns)
- Septicemia
- Otitis media
- Nosocomial infections
Diagnosis
- Culture: Swarming on blood agar, H2S positive on TSI/KIA
- Urease test: Strongly positive
- Phenylalanine deaminase test: Positive
Treatment
- P. mirabilis: usually sensitive to ampicillin, cephalosporins
- P. vulgaris: more resistant → often requires aminoglycosides or fluoroquinolones
- Avoid tetracyclines (ineffective)
- Restrict urinary catheter use to prevent infection