Urinary Tract Infections (UTIs) and Proteus Mirabilis
Proteus mirabilis and UTIs
Proteus mirabilis is a rod-shaped bacterium that lives in the large intestine of many people. It's often harmless and forms a normal part of the gut flora, the useful community of microbes that shares our body with us. Under certain conditions, however, the bacterium can escape from the intestine and cause a urinary tract infection.
Bacteria are routinely shed in the feces. The feces leaves the intestine through an opening called the anus. In women, bacteria may pass from the anus to the nearby urethral opening. Once the microbes enter the urethra they may cause a urinary tract infection, or UTI.
Proteus infections are commonly associated with the formation of stones. The bacterium causes solid crystals to form in urine. Crystals join together to make stones. Small stones may leave the body on their own. Large ones may become trapped in the urinary tract and obstruct urine flow. They may also be very painful.
The Urinary Tract
Structure and Function of the Urinary System
Produces urine by filtering blood and then changing the filtrate's composition by adding and removing substances
Each kidney contains around a million tiny filtering tubes called nephrons.
Drains urine from the kidneys
The renal pelvis is also called the pyelum.
Transports urine from the renal pelvis to the urinary bladder
Stores urine temporarily and then sends it to the urethra
Stretch receptors in the bladder lining "tell" the brain that the bladder is full.
Transports urine from the urinary bladder to the outside world
In a male the urethra transports sperm as well, although not at the same time as urine.
Causes of UTIs and Some Prevention Tips
In women, the anus is behind and close to the urethral opening. It's easy for bacteria to move from the anus to the urethra, which is why hygiene and careful toilet habits are so important. Health experts recommend that women wipe from front to back after defecation to reduce the chance of bacterial entry into the urethra. Bacteria can also enter the urethra from the opening to the reproductive tract, which is located between the anus and the urethral opening.
Women have a far higher incidence of UTIs than men, not only because of the location of their urethral opening but also because their urethra is shorter. A female's urethra is about one and a half inches in length while a male's is about eight inches long. In a female, the bacteria don't have far to travel to reach the urinary bladder and the rest of the urinary tract.
If some bacterial cells do manage to enter the urethra, the flow of urine may be able to flush them away. Urinating when necessary instead of retaining urine is one method used to reduce the chance of a UTI, as is drinking an adequate amount of water. Infections may develop if a large number of bacteria enter the urinary tract. In addition, people with structural abnormalities in the tract that tend to trap fluid are more likely to develop a UTI. In men, an enlarged prostate gland may exert pressure on the urinary tract and prevent adequate fluid flow, increasing the risk of an infection.
Catheters and Urinary Tract Infections
People who have a catheter in the urethra have an increased risk of a UTI. A catheter is a medical device that drains urine from the body. It's a flexible tube that is placed in the urethra, positioned over the urethral opening or connected to the bladder to drain urine from the body. The urine enters a drainage bag. The catheter may be inserted temporarily or may be left in place (an indwelling catheter).
A catheter may be used in situations where it's difficult for a person to urinate normally. Two of these conditions are urinary incontinence and urinary retention. In urinary incontinence a person is unable to stop the release of urine from the bladder, while in urinary retention a person finds it difficult to release urine. A catheter is also used when there is spinal cord damage which prevents the normal process of urination or when a person is temporarily incapacitated in hospital.
Catheters are very useful devices. Unfortunately, the catheter surface may become coated with a film of bacteria that is hard to remove and becomes a continuous source of infection.
Possible Symptoms of a Urinary Tract Infection
A person may have no symptoms of a urinary tract infection. However, there may be unpleasant symptoms, such as:
- a strong and frequent urge to urinate
- a burning pain during urination
- pain or pressure in the lower abdomen
- cloudy urine
- blood in the urine
- strong-smelling urine
- a low-grade fever
If the infection spreads to the kidneys, a person may experience additional symptoms. These include a high fever, shaking and chills, back pain, nausea and vomiting.
Anyone with symptoms of a urinary tract infection should visit a doctor. An untreated infection may have serious consequences. These include kidney damage or failure and infection and inflammation in the bloodstream, which is known as sepsis.
Treatment and Prevention of UTIs in Women
Proteus mirabilis is an interesting, single-celled bacterium that exists in two different forms. These forms are known as swimmer cells and swarmer cells. Swimmer cells are rod-shaped and have eight to ten thin, whip-like extensions called flagella. The flagella enable the bacterium to move through a liquid. Each cell is one or two micrometers in length. A micrometer (µm) is a millionth of a meter or a thousandth of a millimeter.
When the swimmer cells settle on a surface their structure changes. They become much longer - up to eighty µm in length - and develop many more flagella. The flagella are very thin and may not be visible in photos or videos. The cells are now known as swarmer cells. The swarmer cells form an arrangement called a raft. In the raft, the flagella of neighboring cells become interwoven. The bacteria in the raft coordinate their movements and the raft as a whole moves rapidly over a surface, acting almost like a multicellular creature.
Swarming Proteus mirabilis
Bacteria and Urinary Tract Infections
Proteus UTIs are rare in people with normal urinary tracts, although they do occur. Escherichia coli urinary tract infections are far more frequent in this group of people. Proteus mirabilis infections are more common in people with structural abnormalities in their urinary tract that trap urine or in people who have a urinary catheter inserted in their body for a long period of time.
Proteus exhibits interesting behavior that may harm its host.
- The bacterium contains an endotoxin in its cell wall. The toxin causes an inflammatory response in the host when it's released.
- Fimbriae on the cell wall of the bacterium help it to adhere to the urinary tract lining and other surfaces.
- The bacterium can form stationary films on top of surfaces, including urinary catheters. Bacteria in films (biofilms) are harder to eradicate than free-living bacteria because they secrete a slime that protects their bodies.
- Proteus triggers the formation of mineral stones and crusts in the urinary tract of its host.
More Information About UTIs in Men and Women
Proteus mirabilis and Urinary Stones
Most people infected by Proteus mirabilis have stones in their urinary tract. Proteus releases an enzyme called urease. Urease acts on urea, a waste substance in urine. It converts the urea into ammonia, a basic (alkaline) substance that causes the pH to rise. The increased pH triggers calcium phosphate in urine to become solid and form apatite crystals. It also triggers magnesium ammonium phospate to soldify, forming struvite crystals.
Crystals aggregate to form stones, which may block the flow of urine. Bacteria of multiple species may enter crevices in the stones and become difficult to eradicate with antibiotics. The crystals may also form crusts on the inside and outside of catheters. Crusts inside a catheter can interfere with urine flow.
Stones not only act as a reservoir for bacteria but also increase the chance of an infection spreading up the urinary tract to the urinary bladder. Bacteria may enter the pelvis of the kidneys and even the kidneys themselves, where they form new stones. Cystitis (infection and inflammation of the urinary bladder) and pyelonephritis (infection of the renal pelvis and kidneys) are common in people who have stones in the urinary tract.
Treatment of a UTI
Antibiotics are generally used to treat urinary tract infections. Catheters may be removed, at least until the infection has been cured. Once a person is better, a new catheter may be inserted if this is absolutely necessary. Stones may be broken up by a process called shockwave lithotripsy. Surgery may be necessary to remove large stones, however.
In the future, a vaccine may be created to prevent a Proteus mirabilis infection in the urinary tract. A vaccine would be very helpful, since the infection is common in certain groups of people and is sometimes challenging to treat.
References and Further Reading
Questions & Answers
© 2013 Linda Crampton