To diagnose illness caused by E. coli infection, your doctor sends a sample of your stool to a laboratory to test for the presence of E. coli bacteria. The bacteria may be cultured to confirm the diagnosis and identify specific toxins, such as those produced by E.

Coli will appear pink in color. The absence of this (of purple color) is indicative of Gram-positive bacteria and the absence of Gram-negative E.

coli can be identified by fluorescence in the UV. MacConkey-Sorbitol Agar is a growth media, which is used for the selective detection and differentiation of Escherichia coli in water samples.

E coli are rod-shaped bacteria, distinguished from most other coliforms by their ability to ferment lactose at 44°C, and by their growth characteristics on certain media.

coli) | Microbe Notes….Biochemical Test of Escherichia coli (E. coli)

Escherichia coli is capable of fermenting glucose as are Proteus mirabilis (far right) and Shigella dysenteriae (far left). Pseudomonas aeruginosa (center) is a nonfermenter.

E. coli are facultative anaerobic, Gram-negative bacilli that will ferment lactose to produce hydrogen sulfide. Up to 10% of isolates have historically been reported to be slow or non-lactose fermenting, though clinical differences are unknown.

Coli had only one means of utilizing lactose, and that when this genetic activity was shut off, these bacteria would not be able to survive on lactose. Coli has an alternative means of processing lactose. In particular, the genes used by these bacteria to process carbon disulfides can also be used to process lactose.

Altogether, MacConkey agar only grows gram-negative bacteria, and those bacteria will appear differently based on their lactose fermenting ability as well as the rate of fermentation and the presence of a capsule or not.

On EMB if E. coli is grown it will give a distinctive metallic green sheen (due to the metachromatic properties of the dyes, E. coli movement using flagella, and strong acid end-products of fermentation). Some species of Citrobacter and Enterobacter will also react this way to EMB.

Of the five general groups of bacteria that comprise the total coliforms, only E. coli is generally not found growing and reproducing in the environment. Consequently, E. coli is considered to be the species of coliform bacteria that is the best indicator of fecal pollution and the possible presence of pathogens.

Result Interpretation on MacConkey Agar Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter appearance of the medium.

Result Interpretation on MacConkey Agar

Blood agar is an enriched, bacterial growth medium. Fastidious organisms, such as streptococci, do not grow well on ordinary growth media. Blood agar is a type of growth medium (trypticase soy agar enriched with 5% sheep blood) that encourages the growth of bacteria, such as streptococci, that otherwise wouldn’t grow.

Media used for Salmonella identification are those used for identification of all Enterobacteriaceae. Most Salmonella strains are motile with peritrichous flagella, however, nonmotile variants may occur occasionally. Most strains grow on nutrient agar as smooth colonies, 2-4 mm in diameter.

coli on Nutrient Agar (NA) 1. They appear large, circular, low convex, grayish, white, moist, smooth, and opaque.

Blood agar – Colonies are moist and 2-3mm in diameter. CLED agar – Salmonella species are lactose non fermenters (some serotypes e.g. Salmonella Arizonae and Salmonella Indiana may ferment lactose).

Blood Agar is used to grow a wide range of pathogens particularly those that are more difficult to grow such as Haemophilus influenzae, Streptococcus pneumoniae and Neisseria species. It is also required to detect and differentiate haemolytic bacteria, especially Streptococcus species.

DNA sequencing – to identify bacteria, moulds and yeasts. Riboprinter analysis – for bacterial identification and characterisation. Repeat–based polymerase chain reaction – for assessing the similarity of microorganisms. Rapid pathogen confirmation by polymerase chain reaction.

There are three types of hemolysis, designated alpha, beta and gamma. Alpha hemolysis is a greenish discoloration that surrounds a bacterial colony growing on the agar. This type of hemolysis represents a partial decomposition of the hemoglobin of the red blood cells.

Do all bacteria that grow on blood agar break down the blood? No, the only thing that grows on blood agar is the bacteria because it breaks down RBCs. Blood agar is a differential medium because all the bacteria will grow on it due to the nutrients and iron.

Red blood cells without (left and middle) and with (right) hemolysis. If as little as 0.5% of the red blood cells are hemolyzed, the released hemoglobin will cause the serum or plasma to appear pale red or cherry red in color.

This is referred to as α-hemolysis (alpha hemolysis). The greenish color is caused by the presence of biliverdin, which is a by-product of the breakdown of hemoglobin. If the organism does not produce hemolysins and does not break down the blood cells, no clearing will occur.

Blood agar is useful as a primary isolation medium because it supports the growth of about any bacteria. It is nonselective and is used for primary isolation purposes for aerobic and anaerobic cultures in lab.