The flora of the major body systems

The female reproductive and urinary tract

The female reproductive tract is another organ system in which the normal microbial flora is developmentally and age related.  As the infant passes through the birth canal she picks up microorganisms representative of the adult reproductive tract.  The pH of the infant of about one month of age is about 7.0 and the microbial flora is quite diverse with no single organism being dominant.  Among the most common organisms isolated areStaphylococcus epidermidis, and coryneform bacteria and secies of the genera Peptostreptococcus, Bacteroides, Clostridium and Eubacterium(Wilson, 2005).  After puberty the lining of the vagina begins to secrete glycogen, a polysaccharide that favors the colonization and growth of lactobacilli. The Lactobacilli are typically the dominant but far from the only organisms present in the vagina these include the Lactobacilli, Staphylococci, Coryneform bacteria Candida, Streptococcus spp. Gardnerellavaginalis, Ureaplasma spp., Bacteroides, Veillonella spp., Bifidobacterium spp., and Clostridium.  Wilson reports that among 5000 isolates from a population of 54 healthy adult women, ninety-four species representing forty genera were found (2005).

Protective mechanisms of the proximal reproductive tract

The fermentation of glucose derived from the enzymatic hydrolysis of glycogen and fermentation of the resultant glucose by Lactobacillus results in a lowering of the vaginal pH.  This inturn is believed to protect women from colonization by many other potentially pathogenic bacteria.  This protection diminishes after menopause when glycogen secretion and the microbial flora return to prepubescent levels.

The reproductive tract is also unusual in that the distal portions (vagina, cervix) are heavily colonized with a variety of microorganisms while the proximal portions (uterus, fallopian tubes, and ovaries), under normal conditions, remain sterile. This suggests the presence of a microbial barrier system that effectively prevents microbes from invading more protected areas.  The dividing line lies at the uterus at a point where endogenous defense mechanisms both innate and acquired are sufficient to prevent invasion of these privileged areas.

This partition between colonized and sterile regions of the body is a biological necessity.  Microbial invasion of the fallopian tubes is often accompanied by scaring that can cause reproductive sterility, and colonization of the normally sterile uterus can result in death of the egg, a failure of the fertilized egg to implant in the uterine lining or infectious abortion of the developing embryo.

The urinary bladder

The urinary bladder in a healthy female is generally sterile. The resident flora is confined to the distal one third of the urethra connecting the bladder with the vagina.   Being in direct contact with the vagina it is not surprising that the resident flora of the urethra closely resembles that organ.   Some of these organisms are lactobacilli, coagulase negative staphylococci, coryneform bacteria, viridans group streptococci certain anaerobes like Bacteroides spp. Gram positive anaerobic cocci, and various representatives of the cell wall deficient Mollicutes.The maintenance of this population in its normal location in the lower third of the urethra is brought about by a variety of mechanisms including desquamation, which carries away surface associated bacterial populations, by the flow of urine which removes poorly attached bacteria from the surface of the urethra.  The urethra also secretes mucus, which prevents bacteria from adhering directly to the urethral epithelium.
The relatively low pH of urine and its high osmolarity may also inhibit the growth of microorganisms.

The kidneys secrete a protein called uromodulin, which is secreted in the urine and contains receptor sites for the adhesins of certain enterobacteria, especially the pili of Escherichia coli a common opportunistic pathogen of the urinary tract.  The binding of E. coli to this protein prevents adhesion to the uroepithelium itself.  The protein with attached bacteria also may bind to white blood cells increasing the efficiency of phagocytosis.

The disturbance and redistribution of the normal microbial population during sexual intercourse is another challenge that must be met by the female reproductive tract.  The common infection of the urinary tract called honeymoon cystitis(HC) is typically a consequence of frequent and prolonged sexual intercourse.  Although this infection can occur at any time once a female becomes sexually active it frequently occurs on the honeymoon. Technically a urethritis, HC is characterized by pain or a burning feeling during urination and cloudy and often blood tinged urine.  The most common microorganism associated with HC is E. coli, an inhabitant of the gut.  The close approximation of the anus and the vaginal opening makes occasional cross contamination a virtual certainty.  E. coli contamination of the vagina combined with the forceful redistribution of microorganisms during intercourse makes infection of the urethra quite common.