Growth Requirements of E. coli

In growing a bacteria there must be consideration of factors that helps the cell grow, or synthesize. Growth factors that include all the nutrients required by the organism to be cultivated, and such factors as pH, temperature and aeration. Agar,is a good medium where microbes are capable to grow in them, this is an extract form marine alga.

First factor to consider is its nutrients,A very good medium includes the exact and accurate qualities and amount of concentrations in every component f the medium, to make the bacteria adapt to its new environment. Otherwise, it is much cheaper and simpler to use natural materials such as yeast extract, protein digest, or similar substances. A factor to consider is the Hydrogen Ion Concentration (pH)A, where it is very important to determine the optimum range they can grow in. Most organisms grow best at a pH of 6.0-8.0, although some forms have optima as low as pH 3.0 and others have optima as high as pH 10.5. Another factor is temperature, microorganisms vary on the range of the temperature they are capable to grow in with such as psychrophilic forms grows best at low temperature( 15-20 C) mesophilic forms grow best at 30-37 C; and most thermophilic forms grow best at 50-60C. Proper aeration & ionic Strength & Osmotic Pressure are also factors affecting the growth of bacteria.

Escherichia coli occurs in enormous numbers in normal feces and is widely distributed in the intestinal canal of animals and humans. Ordinarily it does no harm.

Extensive studies of bacteria in the feces of infants with diarrhea indicate that many cases of infant diarrhea are due to certain particular kinds of Escherichia coli. These pathogenic E. coli can be distinguished from less harmful varieties by immunologic studies of their antigenic nature. 14 enteropathogenic E. coli serotypes are generally recognized. In a study by Rantz it is pointed out that in patients with urinary infections, about 45% of these infections were acquired in the hospital as the result of catheterization.

Since Escherichia coli is always present in feces, and since other species of Escherichiae tribe frequently accompany it and closely resemble it, this tribe is frequently referred to as "the coliform group." They are easily cultivated and recognized and usually remain alive in foods and water for considerable periods of time. The coliform group is therefore commonly sought after in bacteriologic examinations of water, milk, and food as evidence of fecal pollution, rather than Salmonella or Shigella.

Enterotoxic E. coli

Some strains of E. coli produce two kinds of soluble endotoxin, one heat-labile and antigenic, that acts somewhat like cholera toxin, causing severe diarrhea in humans. These enterotoxic strains should be considered as a distinct group of enteropathogenic E. coli; they differ serologically from the common H and O varieties that do not produce any soluble exotoxin.

Since the coliforms rapidly ferment lactose with the production of acid and gas, measured portions of the suspected water are put into broth containing lactose. If gas is present after 24 to 48 hours, it is not necessarily due to coliform species. Several other organisms also produce gas from lactose. Plates or tubes of selective medium are therefore inoculated from the lactose-broth tubes showing gas. After incubation, colonies resembling those of the cloriform group are selected for pure-culture study and are subjected to simple biochemical tests that easily identify them.

source:  Revised by Robert Fuerst, PhD. (1978). Frobisher and Fuerst's Microbiology in health and disease. (14th ed.). West Washington Square, Philadelphia: W.D. Saunders Company.

source :Brock,Thomas D. Biology of microorganisms.6th ed. Englewood Cliffs, N.J.