What Is Urinary Tract Infection?


What Is Urinary Tract Infection?

MICROBIAL DISEASES species, and is usually found in only small numbers in the bower. anatomic regions proximal to the cardia of the stomach and distal to the ileocecal valve, recent studies have demonstrated organisms in the jejunum and almost always in the ileum; Moderate changes in the diet do not affect the ratio of predominant bacteria in the feces, but antimicrobial therapy has a strong selective effect and is the single most important reason for the increasing emergence in human infection of these heretofore unusual Urinary organisms.

All the micro-organisms of the gastrointestinal tract are potentially pathogenic under conditions of altered host resistance. The major diagnostic problem is to differentiate superficial colonization from actual tissue invasion. Endotoxins. The gram-negative bacteria of the gastrointestinal tract produce disease by the invasion of tissue and by the release of a pharmacologically active lipopolysaCcharide from the cell wall, known as endotoxin. EndOtoxins from a wide variety of unrelated species behave quite similarly, regardless of the inherent pathogenicity of .the micro-organism from which they are de-rived or their antigenic structure. In the intact micro-organism, they exist as corn-, plexes of lipid, polysaccharide, and protein.

The biologic activity seems to be a property of the lipid and carbohydrate portions. When inoculated intravenously, the endotOXins cause fever, leukopenia, circulatory collapse; capillary hemorrhages, necrosis of tumors, and the Shwartzman phenomenon. Noteworthy is the remarkable tolerance that develops after repeated injections of endotoxin. For example, the first intravenous injection in a man of as little as 0.01 ml. of typhoid vaccine will give rise to a violent response, with chill and high fever; yet after 10 to 14 daily injections of increasing quantities, the subject can accept 25 ml. or more without symptoms and with only a slight rise in temperature. This state of tolerance is not obviously dependent on specific antibodies; it ex-tends to endotoxins of unrelated bacterial strains.

The clinical-features of graM-negative bacteremia (vide infra)'resemble the reaction of laboratory animals or man to intravenous injection of purified endotoxic preparations, and may well represent a direct “pharmacologic” response to bacterial. endotoxin. In .other ‘types of infectious proCesS, there is reason to doubt that such phenomena as fever, leukocytosis, and leukopenia are direct effects of endotoxin liberation:

The phenomenon of endotoxin. tolerance may explain the remarkable tendency-of the symptoms of pyelonephritiS to subside spontaneously. By contrast, endotoxin tolerance is not a feature of experimental typhoid fever; ‘but, rather, volunteers infected with this organism have been Shown' to be hypersensitive to its effects. ElidotOxin tolerance is currently under intensive study because of the presumed important pathologic effect of this substance. Tolerance may be due to enhanced removal by the reticuloendothelial system, enzymatic -degradation, cellular desensitization, a common immunologic factor, or combinations of these. Antibodies.

Antibodies reacting with most Enterobacteriaceae can be demonstrated in sera of normal animals and man, probably .because of the continual production of antigen in the gastrointestinal tract. Antibodies to the 0 or somatic antigens of E. coli have been most extensively studied. Very low titers are present in human newborns, presumably because they are mostly of the high molecular weight IgM variety, and do not readily pass the placenta. Human colostrum is rich in 0 antibodies, but this is not absorbed during breastfeeding.

Colonization of the digestive tract, however, is soon accompanied by the appearance of a wide variety of antibodies in serum, which contains virtually all the E. coli 0 antibodies by one year of age. Serologic response to the specific 0 antigens of the invading strain of E. coli can be demonstrated in acute pyelonephritis. It is likely that the great susceptibility of the new-born to overwhelming gram-negative bacterial sepsis is related to a lack of maternal antibodies. As a rule, most strains are susceptible to opsonization and lysis by the combined effects of antibody and complement. Some strains, however, seem insusceptible to lysis in vitro. Nonetheless, this system may be of great importance in preventing strains from invading and persisting in the blood. 

Signs of inflammation of the bladder (cystitis) or kidneys (pyelonephritis). Infections of the structures of the urinary tract are usually accompanied by colonization of the urine which bathes the kidney, ureter, ‘bladder, and urethra. Thus, bacteriuria is the most common denominator of ‘urinary tract infections. Bacteriuria may be absent, however, when the infected focus is not contiguous with the urine as in early lesions of hematogenous pyelonephritis when there is marked obstruction of the affected portion of the tractor when it is masked by antimicrobial

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