Infections of the Urinary System

Published on 02/03/2015 by admin

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Last modified 02/03/2015

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Infections of the Urinary System



As far back as 3000 bce, the Chinese recognized infections and diseases involving the urinary tract and developed an extensive list of herbal remedies. One of the most comprehensive ancient documents dealing with urinary tract infections and potential cures was the Ebers papyrus written in Egypt at about 1550 bce. This document identified the illness and potential herbal cures but did not offer any attempts to explain the actual causes of these infections. In ancient Greece, Hippocrates (460–375 bce) offered an explanation for urinary tract infections that involved an imbalance in the four humors of the body. He noted the presence of sand in urine that came from the consumption of contaminated water by the individual, which eventually led to the formation of stones, blocking the elimination of urine. This blockage caused the imbalance in the humors and the resultant disease. It was not until the mid-nineteenth century that Pasteur documented that microorganisms were responsible for the contamination of urine associated with urinary tract infections. Treatments at this time primarily involved the use of chemicals that altered the pH of the urinary bladder and the lower urinary tract. The development of antibiotics in the twentieth century resulted in modern regimens for effective treatment of urinary tract infections.


The urinary system consists of the kidneys, ureters, urinary bladder, and urethra (Figure 15.1). The kidneys are the central organ of the system and are responsible for filtering wastes from the blood as well as for removing any excess liquid, thus forming urine. The functional units in the kidneys are the nephrons (Figure 15.2) and in addition to their filtering capacity they also keep a stable balance of minerals, salts, and other substances to maintain the homeostasis (the maintenance of a relatively stable environment of the body) of the blood. Furthermore, the kidneys produce erythropoietin, the hormone that aids in the formation of red blood cells. The ureters are narrow tubes that carry the urine from the kidneys to the urinary bladder, which stores the urine for later expulsion from the body. The urine stored in the urinary bladder is emptied through the urethra, whose length varies between male and female. The male urethra is longer than the female and the opening is located on the penis. Normally urine is sterile, free of any microorganisms; however, an infection can occur when infectious organisms, usually bacteria from the gastrointestinal tract, gain access to the opening of the urethra and multiply. The urinary tract is one of the most common sites of bacterial infection, particularly in females.

Urinary Tract Infections (UTIs)

There are a number of organisms that can be responsible for a urinary tract infection (UTI) infection but the most common is Escherichia coli, a gram-negative, facultatively anaerobic rod that can thrive in a relatively wide range of pH. The infection may remain localized in the urethra, but the organisms can also travel up the urethra and infect the urinary bladder. When a urinary bladder infection is not treated, it may spread to the kidneys. In a small number of cases, UTIs have been caused by organisms that originated in oral/gum infections. In these cases the organisms traveled through the bloodstream to the kidneys, where they gave rise to a kidney infection. In healthy individuals the urinary system is designed to prevent urine from backing up from the urinary bladder to the ureters and kidneys, and the flow of urine from the bladder typically helps wash away any microorganisms. The prostate gland in men also produces slightly acidic secretions that tend to slow bacterial growth. These structural and chemical mechanisms, along with the actions of a healthy immune system, are normally effective at preventing UTIs. The type of infection is typically defined by the organ or structure where the infection is located.

Organisms that cause UTIs may be sexually transmitted and the infections usually remain limited to the urethra and the organs of the reproductive system. Not all individuals with a UTI show easily recognizable symptoms, but most cases include the following:

Other symptoms may vary among individuals and depend on the specific type of infection. These symptoms may include the following:

Urinary tract infections are identified by the specific location or organ being affected by the microorganisms. The most common infections are urethritis, cystitis, pyelonephritis, leptospirosis, and glomerulonephritis.

Diagnosis of UTIs

Typically the detection/diagnosis process occurs in two stages. The first stage involves gathering a sample of urine for evaluation and the second stage involves testing the antibiotic sensitivity of any microorganisms that may be present. The collection of urine involves a procedure called a “clean catch,” wherein the patient thoroughly washes the genital area and then collects a midstream sample in a sterile container. The sample can then be both cultured for microbial growth as well as examined microscopically to determine the presence of microbes, pus, or blood. Typically the urine sample is streaked on a blood agar plate, using a special pattern to provide a semiquantitative analysis of the sample (Figure 15.3). If microbial growth occurs on the growth medium, the organisms can be tested with various antibiotics to identify the most effective one against a specific pathogen. This step is called a sensitivity test. The general term for the presence of bacteria in the urine is bacteriuria.

Risk Factors for UTIs

The risk factors for UTIs vary from individual to individual and from situation to situation; however, there appear to be certain factors that are common in many patients. The following groups exhibit unique risk factors: