Bacterial Diseases of the Urinary System


Bacterial Diseases of the Urinary System

  • Urinary system infections are most frequently initiated by an inflammation of the urethra, or urethritis.
  • Infection of the urinary bladder is called cystitis, and infection of the ureters is ureteritis.
  • The most significant danger from lower urinary tract infections is that they may move up the ureters and affect the kidneys, causing pyelonephritis.
  • Occasionally the kidneys are affected by systemic bacterial diseases, such as leptospirosis.
  • The pathogens causing these diseases are found in excreted urine.
  • Bacterial infections of the urinary system are caused by different microbes that enter the system from external sources.
  • In the United States there are about 7 million urinary tract infections each year.
  • Approx 900,000 cases are of nosocomial origin infection, and probably 90% of these are associated with urinary catheters.
  • Because of the proximity of the anus to the urinary opening, intestinal bacteria predominate in urinary tract infections.
  • Most infections of the urinary tract are caused by different strain Escherichia coli.
  • Infections by Pseudomonas, because of their natural resistance to antibiotics, are especially troublesome.




  • Cystitis is a common inflammation of the urinary bladder in females.
  • Symptoms often include dysuria (difficult, painful, urgent urination) and pyuria.
  • The female urethra is less than 2 inches long, and microorganisms traverse it readily.
  • It is also closer than the male urethra to the anal opening and its contaminating intestinal bacteria.
  • These considerations are reflected in the fact that the rate of urinary tract infections in women is eight times that of men.
  • In either gender, most cases are due to infection by E. coli, which can be identified by cultivation on differential media such as MacConkey’s agar: (Interestingly, daily ingestion of cranberry juice prevents E. coli from adhering to epithelial cells) .



  • As a general rule, a urine sample with more than 100 colony forming units (CFUs) per milliliter of potential pathogens (such as coliforms) from a female patient with cystitis is considered significant.
  • The diagnosis also include a positive urine test for leukocyte esterase (LE), an enzyme produced by neutrophils which indicates an active infection.
  • Trimethoprim-sulfamethoxazole usually clears cases of cystitis quickly.
  • Fluoroquinolone antibiotics or ampicillin are often successful if drug resistance is encountered.


  • In 25% of untreated cases, cystitis may progress to pyelonephritis, an inflammation of  kidneys.
  • Symptoms are fever and flank or back pain.
  • In females, it is a complication of lower urinary tract infections.
  • The causative agent is about 75% of the cases in E. coli.
  • Pyelonephritis generally results in bacteremia; blood cultures and a Gram stain of the urine for bacteria are useful for diagnosis.
  • A urine sample more than 10,000 CFUs/ml and a positive LE test indicate pyelonephritis.
  • If pyelonephritis becomes chronic, scar tissue forms in the kidneys and severely impairs their function.
  • Because pyelonephritis is a potentially life – threatening condition, treatment usually begins with intravenous, extendedterm administration of a broad-spectrum antibiotic, such as asecond- or third-generation cephalosporin.


  • Leptospirosis is primarily a disease of domestic or wild animals, but it can be passed to humans and sometimes causes severe kidney or liver disease.
  • The causative agent is the spirochete Leptospira interrogalls.
  • Leptospira has a characteristic shape: an exceedingly fine spiral, only about 0.1 μm in diameter.
  • Animals infected with the spirochete shed the bacteria in their urine for extended periods.
  • Humans become infected by contact with urine contaminated soil or water or sometimes with tissue of animals.

  • People whose occupations expose them to animals or animal products are most at risk.
  • Usually the pathogen enters through minor abrasions in the skin or mucous membranes.
  • When ingested, it enters through the mucosa of the upper digestive system.
  • In the United States, dogs and rats are the most common sources.
  • Domestic dogs have a sizable rate of infection; even when immunized, they may continue to shed leptospira.


  • After an incubation period of 1 to 2 weeks, headaches, muscular aches, chills, and fever abruptly appear.
  • Several days later, the acute symptoms disappear, and the temperature returns to normal.
  • A few days later, however, a second episode of fever may occur. In a small number of cases the kidneys and liver become seriously infected (Weil’s disease); kidney failure is the most common cause of death.


  • Most cases of leptospirosis are diagnosed by a serological test that is complicated and usually done by central reference laboratories.
  • However, a number of rapid serological tests are available for a preliminary diagnosis.
  • Also, a diagnosis can be made by sampling blood, urine, or other fluids for the organism or its DNA.


  • Doxycyline (a tetracycline) is the antibiotic for treatment; however, administration of antibiotics in later stages is often unsatisfactory.

Bacterial Diseases of the Urinary System


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