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.