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.