Proteus mirabilis is a gram-negative bacteria, which is a part of the normal flora of the gut. It is also abundantly in soil in water. It is most associated with UTIs, but can also lead to septicemia, pneumonia and wound infections in hospitalized patients.
This bacterium is rod-shaped, or a bacillus. It is also notable that proteus mirabilis is facultatively anaerobic.
Proteus mirabilis is oxidase negative, meaning this bacterium does not contain cytochrome c oxidase. It cannot use oxygen for energy production, and leads to a colorless reagent when tested.
This bacteria has the ability to produce urease, which hydrolizes urea in the body to ammonia. In a urinary tract infection, this means that the urine becomes more alkaline. In the lab, these bacteria produce a very distinct, fishy odor.
These bacteria are able to be easily diagnosed on agar, as they show characteristic "swarming motility."
This bacterium cannot utilize lactose, and does not ferment when exposed to it. Rather, in the MacConkey agar in which this trait is tested for, Proteus mirabilis uses peptone instead of lactose, forming ammonia, which in turn raises the pH of the agar. This causes Proteus grow as white/colorless colonies on MacConkey agar.
These bacteria are a normal part of the gut's flora, but can infect the urinary tract. These urease producing bacteria, when causing a UTI, lead to alkalinized urine, which can then cause kidney stones (often staghorn calculi).
These bacteria can alkalinize the urine, leading to formation of crystals, such as struvite, which is also called magnesium ammonium phosphate. Struvite crystals are characteristic of this infection, and often grow into large staghorn calculi, which cause renal obstruction and renal failure.
Staghorn calculi are upper urinary tract stones that involve the renal pelvis and extend into at least two of the calyces. All types of urinary stones can potential form staghorn calculi, but the majority of them are composed of struvite-carbonate-apatite.
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