Proteus mirabilis is a type of bacterium commonly found in natural environments like soil and water, and it resides within the human gut. This microorganism is a Gram-negative, rod-shaped bacterium, meaning it has a specific cell wall structure and an elongated, cylindrical form. While often part of the normal bacterial community, Proteus mirabilis can act as an opportunistic pathogen, causing infections when conditions are favorable. It is particularly recognized for its involvement in urinary tract infections.
Unique Features and Natural Environment
Proteus mirabilis possesses several distinctive biological characteristics. One notable feature is its remarkable “swarming motility,” a specialized form of movement where groups of these flagellated bacteria migrate coordinately across solid surfaces. This swarming allows the bacterium to spread rapidly, forming distinctive patterns on laboratory growth media and facilitating its movement across surfaces like medical devices. The bacterium differentiates into elongated swarm cells with numerous flagella, enabling this multicellular migration.
Another characteristic of Proteus mirabilis is its ability to produce urease, an enzyme that breaks down urea. This enzymatic activity is significant because it alters the local environment, particularly in the urinary tract, by increasing the pH. Its optimal growth temperature (34-37°C) makes the human body an ideal host. Proteus mirabilis is widely distributed in soil and water, and it is also a common inhabitant of the gastrointestinal tract in both humans and animals.
Infections and Health Impact
Proteus mirabilis is a common cause of urinary tract infections (UTIs), especially in individuals with catheters or underlying urinary tract issues. In otherwise healthy women, it accounts for 1% to 2% of all UTIs, but this percentage can rise significantly to 20% to 45% in complicated UTIs, such as those associated with catheterization. Its urease activity plays a substantial role in these infections, leading to the hydrolysis of urea into ammonia, which increases urine alkalinity. This alkaline environment promotes the precipitation of magnesium and calcium, resulting in the formation of struvite kidney stones.
These kidney stones can obstruct urinary flow, provide a protective niche for bacteria, and contribute to recurrent infections. Symptoms of UTIs caused by Proteus mirabilis can include painful urination (dysuria), frequent urination, cloudy urine, and lower abdominal or back pain. If the infection progresses to the kidneys (pyelonephritis), symptoms can become more severe, potentially including fever, chills, flank pain, and nausea. In severe cases, Proteus mirabilis infections can also lead to bacteremia, where the bacteria enter the bloodstream, causing systemic symptoms like fever, chills, and low blood pressure, which can progress to sepsis. Beyond UTIs, Proteus mirabilis can also cause wound infections, presenting with pus discharge, redness, and swelling.
Diagnosis and Management
Diagnosing Proteus mirabilis infections typically involves laboratory tests to identify the bacterium. Urine cultures are a common method for urinary tract infections, where urine is cultured to isolate and identify bacteria. Doctors look for characteristic signs, such as the bacterium’s distinctive swarming motility and its inability to ferment lactose, which help differentiate it from other bacteria. Additionally, a persistently alkaline urine sample can suggest a Proteus mirabilis infection due to its urease activity.
Treatment for Proteus mirabilis infections generally involves antibiotics, chosen based on infection severity and bacterial susceptibility. For uncomplicated urinary tract infections, oral antibiotics like trimethoprim-sulfamethoxazole or fluoroquinolones may be prescribed for a few days. More severe or complicated infections, such as pyelonephritis, might require intravenous antibiotics initially, followed by a longer course of oral medication. However, antibiotic resistance is a growing concern, as Proteus mirabilis strains can develop resistance to various antibiotics.
Susceptibility testing is crucial to determine effective antibiotics. Proper antibiotic use, guided by these tests, is important to ensure effective treatment and to help slow the development of further resistance. Preventive measures for recurrent infections often focus on minimizing risk factors, such as avoiding prolonged catheterization and maintaining good hygiene. For patients with kidney stones caused by Proteus mirabilis, complete stone removal may be necessary alongside antibiotic therapy to prevent recurrent infections and complications.