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Vesico-ureteric reflux

outflow obstruction is a major factor and may be due to bladder neck stenosis, urethral stricture or prostatic enlargement. The particular susceptibility of women is due partly to the short urethra and its proximity to the bowel.

The virulence of an organism is related to its ability to adhere to epithelial cells. Less virulent organisms may be pathogenic when the kidney is not normal, e.g. with vesico-ureteric reflux. The epithelial cell receptors for the majority of uropatho-genic E. coli strains are glycolipids of the globo-series, which interact with adhesins on the bacterial surface. The adhesins are filamentous appendages called fimbriae. The two main types are distinguished by whether their binding to red cells is inhibited by mannose or not. The receptor glycolipids are antigens in the P blood group system with the phenotype PI as the major binding sites. E. coli express both O and K antigens and the pathogenic strains are associated with relatively few serotypes of these two families.

There are a number of host defense mechanisms against UTIs. The bladder luminal surface is covered with a glycoprotein mucin layer. Disruption of this layer allows bacteria to colonize the epithelium. Bacterial washout by the normal urine flow and bladder emptying is a major defense mechanism. Urinary antibodies (immunoglobulin G (IgG) and secretory IgA) are formed against the O and K serotypes, and with pyelonephritis a systemic antibody response to O antigens occurs.

Clinical infection Acute pyelonephritis

This is associated with fever, malaise, loin pain (which may be bilateral) and bacteruria and leukocy-turia. There may also be symptoms of cystitis. In nor mal kidneys the organisms are E. coli, coagulase-positive Staphylococcus, Streptococcus faecalis and Klebsiella. The presence of other gram-negative organisms (Pseudomonas, Proteus) would suggest pre-existing disease or a stone.

Other acute parenchymal infections

Rarely, septicemia may lead to microabscess formation in the kidney (usually Staph, aureus). Occasionally, with very severe infection, or particularly associated with diabetes, there may be necrosis of the renal papillae (papillary necrosis). Rarely subacute or chronic infections may develop, particularly associated with pre-existing abnormalities of the kidney, and the abscess may extend to form a mass (renal carbuncle) or point through the capsule of the kidney to form a perinephric abscess.

Chronic pyelonephritis

Vesico-ureteric reflux with or without infection may cause scarring of the kidney, and the scarring varies with the degree of reflux. Much of the scarring may have occurred in the fetal or neonatal period, although further scarring in childhood is associated with UTI. In later life progressive damage and renal failure may occur in the absence of both UTIs and reflux and the term reflux nephropathy is now preferred for such cases, rather than the former term chronic pyelonephritis. Ureteric reflux is now recognized as a common inherited disease (autosomal dominant).

Other chronic infections

Complete obstruction may lead to severe infection in the renal pelvis (pyonephrosis) and loss of the kidney. Tuberculosis may involve the renal parenchyma, and this is generally associated with a ureteritis and cystitis. Obstruction with stone disease may be associated with a chronic granulomatous pyelonephritis (xantho-granulomatous pyelonephritis). Malakoplakia is a rare chronic infection of the renal substance which may simulate a renal tumor. It is associated with an inability of macrophages to kill E. coli successfully.

Cystitis

Cystitis is associated with frequency and urgency of micturition and painful micturition (dysuria). Bacterial infection is usually due to E. coli. Chronic cystitis with pyuria but cultures that arc reported as 'sterile' is highly suggestive of tuberculous infection. In some women recurrent symptoms of cystitis occur in the absence of significant bacteruria and pyuria (acute urethral syndrome). The cause is unknown but may be due to fastidious organisms (such as Gard-nerella vaginalis) or organisms that are considered as part of the normal urethral flora.

Urethritis

Urethritis is associated with dysuria and a urethral discharge. Infection from Neisseria gonorrhoeae should be considered; nongonoccal infections (nonspecific urethritis) include Chlamydia trachomatis and Ureaplasma urealyticum.

See also: Chlamydia, infection and immunity; Escherichia coli, infection and immunity; Klebsiella, infec tion and immunity; Neisseria, infection and immunity; Staphylococcus, infection and immunity; Streptococcus, infection and immunity; Urinary tract infections.

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