Urinary Tract Infections - Medical Microbiology

Urinary Tract Infections

The urinary system is composed of organs that regulate the chemical composition and the volume of the blood excrete mostly nitrogenous wastes products and water. The urinary system consists of two kidneys, two ureters, a single urinary bladder and a single urethra. Wastes are removed from the blood as it circulates through the kidneys (Figure 12.15).

Infections of the kidney, ureter and bladder constitute Urinary Tract Infections (UTI). When infection occur in the kidney and ureter it is called upper urinary tract infections and bladder downwards is called lower urinary tract infections. Urinary tract infection is common in females than males. The urinary system normally contains few microbes but it is subjected to opportunistic infections that can be quite troublesome. Almost all such infections are caused by bacteria although occasional infections by pathogens such as parasites, protozoa and fungi also occured. Microorganisms invloved in UTI are listed in Table 12.7.

Predisposing Factors for UTI

Urinary tract infection is common in females than in males. The urethra in females are shorter and wider and is less effective in preventing the bacteria entering the bladder. 

Sexual intercourse is a predisposing factor in females. High incidence is seen in pregnant women due to hormonal changes and impairment of urine flow due to pressure on urinary tract.

Urinary Tract Infection caused by Escherichia coli

Escherichia coli is the predominant cause of UTI.

It is a normal flora of the gut and can cause extra intestinal infections (UTI, Wound infection.) UTI (it can also be involved in other infections like wound infection peritonitis) UTI is common in married women (b) elderly men with prostate enlargement.

Pathogenesis of cystitis in woman

Bladder infections can result from the downward migration of organisms from an infected kidney. But majority arise by ascent of pathogens from the rectum and vagina to the urethra meatus and bladder, leading to cystitis. If left untreated, the infection can further ascend to involve the kidneys (pyelonephritis) (Figure 12.16).

The rectum and vagina function as the reservoir of bacteria for sporadic infections

In men, the longer urethra is believed to protect against ascending infections.

When Escherichia.coli (and other Gram Negative rods) causes UTI, usually the number of organisms in freshly passed urine is more than 100,000 organisms/ml.

This is called “significant bacteriuria”. Counts less than this is associated with contaminants from urethra or externalia. Infection of urinary tract are listed in Table 12.8.