Proteus mirabilis

Proteus mirabilis is a gram-negative facultatively anaerobic bacterium characterized by swarming motility and urease activity. Proteus mirabilis causes 90% of infections of the genus Proteus, which can be considered community-acquired infections.

Occurrence
Proteus mirabilis is part of the normal gastrointestinal flora. It is also found in soil, water, plants, human and animal faeces. Proteus is found in many ecological habitats, including long-term health care facilities and hospitals.

Microbiological characteristics
Proteus mirabilis belongs to the group of enterobacteria. It is a small Gram-negative facultatively anaerobic bacillus. It is characterised by swarming growth on the Endo agar, the ability to ferment maltose, and the inability to ferment lactose. It has the ability to elongate, and when in contact with solid surfaces, it secretes polysaccharides, thus becoming very mobile and spreading to various surfaces, such as medical devices.

Virulence factors
The flagellum of P. mirabilis is critical for its motility and helps the organism colonize. The flagellum is also associated with the bacterium's ability to form a biofilm, aiding in resistance to the host defense and selected antibiotics. P. mirabilis also relies on its pili for attachment to avoid flushing from the urinary tract.

Important to P. mirabilis is urease, responsible for raising the pH and subsequent thriving of the bacteria. There are endotoxins, responsible for the induction of inflammatory reactions, and hemolysin, which forms pores.

Diseases
Most often, infections occur when bacteria move into the urethra and bladder. Although the bacterium Proteus mirabilis is known to cause urinary tract infections, most of these infections are caused by E. coli. Urinary tract infections caused by P. mirabilis are usually found in patients with long-term catheterization. The bacteria moves around and forms encrustations on urinary catheters. The encrustations cause blockage of the catheter.

Symptoms for urethritis are mild, including urinary frequency and pyuria (presence of white blood cells in urine examination). Symptoms of cystitis (bladder infection) include back pain, urgency, hematuria (presence of red blood cells in the urine), suprapubic pain, frequent urination, and pyuria.

Pyelonephritis (infection of the renal glands) can occur when bacteria migrates from the lower urinary tract to the upper urinary tract. Not all patients have symptoms associated with urethritis and cystitis. Pyelonephritis is associated with nausea and vomiting.

The Proteus mirabilis bacteria can enter the bloodstream through a wound (e.g. when the wound comes into contact with an infected surface), causing inflammatory reaction, which can cause sepsis and systemic inflammatory response syndrome (SIRS). SIRS has a mortality rate of 20-50%.

P. mirabilis can also, although less frequently, colonize lungs. This results from interaction with infected hospital equipment (air conditioning) and causes pneumonia. Symptoms of pneumonia are fever, chills, chest pain, murmurs, and cough.

Infection with P. mirabilis may also result in prostatitis, which is characterized by fever and chills. The bacteria may also be the cause of neonatal sepsis and meningitis.

Therapy
The antibiotics of choice for P. mirabilis are usually cephalosporins of 1st and 2nd generation. The bacteria generally manifests high sensitivity to various antibiotics, though furantoin and tetracyclines are the ones it's resistant to.

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