E.coli Metabolism Products on Different Culture Mediums

E. coli typically produces positive tests for indole, lysine decarboxylase, and mannitol fermentation and produces gas from glucose. an isolate from urine can be quickly identified as E. coli by its hemolysis on blood agar typical colonial morphology with an iridescent "sheen" on different media such as EMB agar, and a positive spot indole test.


Lactose fermented rapidly E. coli: Metallic sheen on different media: motile: flat: nonvicous growth


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Source: Brooks, G., Butch, J., & Ornston, N. (1991). Jawetz,Melnick and Adel Berg's Medical Microbiology (19th ed.). United States of America: Appleton and Lange.

Morpholigical Description of E.coli

Escherichia coli is quickly identified in urine by the process of hemolysis that occurs in blood agar.  It is determined in a differential media such as EMB having a morphological feature of an iridescent “sheen”. It gives positive test for indole, lysine decarboxylase, and manitol fermentation and produces gas from glucose.

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. 

All About E.coli

Organism: E-coli

Habitat (reservoir) –normal bowel flora of humans and others animals may also inhabit female genital tract.

Mode of transmission

-          Varies with the type of infection. For non-gastrointestinal infection, organism may be endogenous or ma spread person to person, esp. in the hospital setting ; for gastrointestinal infection, transmission ode varies with the type of E-coli and may involve fecal-oral spread bet. Humans via contaminated food or water or consumption of undercooked beef or milk colonized cattle

Virulence Factor:

Several,including endotoxin , capsule production and pili that mediate attachment to host cells.

Colunial appearance ofen beta hemolytic on blood agar, but most other genera are non- hemolytic.

Colonial appearance and characteristic :

  Mac – LF; flat, dry, pink colonies with a surrounding darker pink area of precipitated bite salts.

HE- yellow

XLD- yellow  

Bacterial and Archaeal Cells Reproduce Asexually

The interval time between successive binary fission of a cells of population of cells I kwon the generation time (double time) . Under optimal condition , some species have a very fast generation time; for others, it is to much slower.

The generation time is useful in determining the amount of time that passes before disease symptom appear in an infected individual; faster division times often mean shooter incubation period for a disease. For example, suppose you eat an undercooked hamburger contaminated with pathogens E.coli 057:H7, which has one of the shortest generation times – just 20 minutes under optimal conditions.

*The number of E. coli cells progress from 1 cell to 2 million cells in a mere 7 hours.  The J-shaped growth curve gets steeper as the hours pass.  Only a depletion of food, build up of waste, or some other limitation will halt the progress of the curve.

Gas producing bacteria. The Genus  aerobacter . The organism belonging to this group are of intestinal and soil origin: Escherichia coli, motile ad without capsule: and Aer. Aerogenes, nin-motle and frequenty  capsulated when grown in milk. And they do not produce spores an and are gram-negative, differing in this latter respect from the other  lactic bacteria. These organism grow readily on ordinary cultured media. The colonies on agar or gelatin plates are easily differentiated from those of the preceding group because they are much larger and inclined to be slimy. The optimum growth temperature is above blood heat, but the organism grow well at lower temperature. In the presence of suitable carbohydrates these organism can developed under anaerobic conditions, but when deprived of sugars they are aerobic.

Presumptive Method. Advantage is taken of certain of the physiological characters of E. coli to differentiate it from the other organism. The media commonly used lactose broth and lactose bile in fermentation tubes. When various amount of water to be examined are inoculated into fermentation tube containing lactose broth kept at blood heat for twenty four hours, gas will be produce on those tubes in which E. coli is present.  It seems safe to infer that E. coli I not present if the gas is not produced in any tubes inoculated. The reverse, however, that E, coli must necessarily be present whenever gas is not produced, does not hold gold for there are other organisms which can ferment lactose with the production of acid gas. The test is more definite when a 2 percent of solution of lactose bile substituted for the lactose broth in tubes. The bile inhibits the growth of the most organism not of intestinal origin. Gas production, under these conditions, therefore in the large proportion cases means that this organism is not present. These tests are termed presumptive tests, because while they enable one to recognized waters which are suspicious, they do not certainly identify the organism responsible for the gas in the suspicious cases.  This permits one, in the words, to divide waters tested into two groups and those which are certainly good and those which are suspect.  The latter require further examination.

The presumptive test is made by inoculation of varying dilutions of the water being assayed into a series of fermentation tubes of lactose broth.  In cases in which detection of coliform organisms in a considerable amount of water, such as fifty or hundred milliliter quantities, is attempted large tubes or bottles must be used in which have been placed amount of double or quadruple strength lactose broth so that upon dilution by the addition of within approximately twenty-four hours at 35 degree -37 degree C is presumptive evidence that coliform organisms were present in forty eight hours but not in twenty hours, the results is classified as doubtful, and a confirmed or completed test is carried through.  If no gas is produced, it is assumed that no coliform bacteria were present in the inoculums.  All cases of doubtful reaction, and preferably positive presumptive reactions as well, should be tested further by use of confirmation test.  A confirmation may be made by transfer of a loop of the broth to any one or more of several media.  It may be streaked on the surface of Endo agar or on eosin methylene blue agar in plates, or inoculated into a tube of brilliant green lactose bile.  If colonies typical of Escherichia coli are produced on the agar or if gas is produced in the brilliant green lactose bile, the presence of coliform organism is confirmed.  If typical colonies only are produced, transfers of such colonies should be made and pure cultures grown on agar slant and in lactose broth.  If the organism belongs to the coliform group stained preparation will show it to be rod-shaped, gram-negative and without spores and gas should be produced in lactose broth.

Identification of Escherichia coli.  Many methods have been devised for the differentiation of the colon bacillus either directly from water or from lactose broth or lactose bile tubes discussed above.  When water containing E coli is plated on agar containing 1 percent lactose and sufficient litmus solution to color it blue, and is then incubated for twenty four hours at blood heat, the lactose fermenting colonies will be found to be surrounded by a red zone.