Unformatted text preview: atory. Molecular techniques are now being used to identify the
nonculturable organisms in this environment.
Organisms living in the lumen of the large intestine are continuously displaced
downward by peristalsis, desquamation of the surface epithelial cells to which they are
attached and the flow of mucus. When they arrive at the anus, they are expelled. An adult
eliminates about 1013 microorganisms daily.
The time needed for passage of material through the complete gastrointestinal tract is
about one day in humans. During the passage of food, water is absorbed from the digested
material, which actually becomes more concentrated and is converted to feces. In the end,
microorganisms make up about one-third of the weight of fecal matter.
Normal adults expel several hundred milliliters of intestinal gas each day (= flatus)
about half of which is N2 from swallowed air. The remainder is composed of odour
causing volatile chemicals (H2S, NH3, amines, certain fatty acids) resulting from microbial
metabolism. Interestingly only about 1/3 of normal adults have methanogenic archaea in
their intestine, so not all human flatus contains methane. FOOD-306 The genitourinary tract
In both males and females, he upper genitourinary tract (kidneys, ureters, bladder) is
sterile, In males, only near the opening of the urethra to the environment are
microbes normally found in the genitourinary tract.This is not the case in females.
Because of its large surface area and mucous secretions, the vagina has a large and complex
normal flora. The vagina is an acidic environment (pH ~ 4). In contrast to stomach acidity
stomach which is generated by the production of HCl by the body itself, low pH of
vaginal fluids is due to fermentative lactic acid production by aerotolerant Lactobacillus
sp. lining the walls of the vagina. This acid pH helps to inhibit growth of other
(pathogenic) microorganisms that could potentially cause vaginal infections. The presence
of Lactobacillus also helps to prevent infections in another way. Because it is present in
large numbers the organism forms a biofilm (coating) over the surface of the vaginal wall
which helps to prevent pathogenic bacteria from finding space to attach to the wall. There
are an estimated 109 bacteria in an average vagina a large proportion of which are
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This note was uploaded on 10/25/2013 for the course MICB 201 taught by Professor Davidturner during the Fall '12 term at UBC.
- Fall '12