Proteus mirabilis

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Proteus mirabilis is a Gram-negative, facultatively anaerobic bacterium. It shows swarming motility, and urease activity. P. mirabilis causes 90% of all 'Proteus' infections. It belongs to the Tribe Proteae.

Diagnosis

An alkaline urine sample is a possible sign of P. mirabilis.

P. mirabilis can be diagnosed in the lab due to characteristic swarming motility, and inability to metabolize lactose (on a MacConkey agar plate, for example.) Also P. mirabilis produces a very distinct odour.

Disease

This rod shaped bacterium has the ability to produce high levels of urease. Urease hydrolyzes urea to ammonia (NH₃) and thus makes the urine more alkaline. If left untreated, the increased alkalinity can lead to the formation of crystals of struvite, calcium carbonate, and/or apatite. The bacteria can be found throughout the stones, and these bacteria lurking in the stones can reinitiate infection after antibiotic treatment. Once the stones develop, over time they may grow large enough to cause obstruction and renal failure. Proteus can also cause wound infections, septicemia and pneumonias, mostly in hospitalized patients.

Treatment

P. mirabilis is generally susceptible to most antibiotics apart from tetracycline, however 10%–20% of P. mirabilis strains are also resistant to first generation cephalosporins and ampicillins.

Characteristics

P. mirabilis can utilize urea and citrate. It can produce hydrogen sulfide gas, and forms clear films on growth media. It is motile, possessing peritrichous flagella, and is known for its swarming ability. It is commonly found in the intestinal tract of humans. P. mirabilis is not pathogenic in guinea pigs or chickens. Noteworthy is the ability of this species to inhibit growth of unrelated strains resulting in a macroscopically visible line of reduced bacterial growth where two swarming strains intersect. This line is named Dienes line after its discoverer Louis Dienes.

The micro-organism tests:

Indole negative and Nitrogen Reductase positive (no gas bubble produced)
Methyl Red positive and Vogues-Proskauer negative
Catalase positive and Cytochrome Oxidase negative
Phenylalanine Deaminase positive

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