Skip to main content

MacConkey Agar

By
MacConkey Agar


MacConkey agar is a selective and differential media used for the isolation and differentiation of non-fastidious gram-negative rods, particularly members of the family Enterobacteriaceae .

Composition



MacConkey agar is used for the isolation of gram-negative enteric bacteria and the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. Pancreatic digest of gelatin and peptones (meat and casein) provide the essential nutrients, vitamins and nitrogenous factors required for growth of microorganisms. Lactose monohydrate is the fermentable source of carbohydrate. The selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria. Sodium chloride maintains the osmotic balance in the medium. Neutral red is a pH indicator that turns red at a pH below 6.8 and is colorless at any pH greater than 6.8. Agar is the solidifying agent.

Uses of MacConkey Agar
1.    MacConkey agar is used for the isolation of gram-negative enteric bacteria.
2.    It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria.
3.    It is used for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens.
Preparation 
1.    Suspend 49.53 grams of dehydrated medium in 1000 ml purified/distilled water.
2.    Heat to boiling to dissolve the medium completely.
3.    Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. 
4.    Cool to 45-50°C.
5.    Mix well before pouring into sterile Petri plates.
Prepare culture
The specimen streaking on macconkey agar.Incubation 37c 18-24h

Image result for mannitol salt agar strin
Result Interpretation

Lactose fermenting strains grow as red or pink and may be surrounded by a zone of acid precipitated bile. The red colour is due to production of acid from lactose, absorption of neutral red and a subsequent colour change of the dye when the pH of medium falls below 6.8.

Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature.

References
http://www.time2026end.com/

Labels:

Comments

Post a Comment

Popular posts from this blog

Triple Sugar Iron Test

By
The Triple Sugar Iron (TSI) Test  To determine the ability of an organism to ferment glucose, lactose, and sucrose, and their ability to produce hydrogen sulfide. Principle The Triple Sugar Iron (TSI) test is a microbiological test named for its ability to test a microorganism’s ability to ferment sugars and to produce hydrogen sulfide. An agar slant of a special medium with multiple sugars constituting a pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose, as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate is used for carrying out the test.  . Due to the building of acid during fermentation, the pH falls. The acid base indicator Phenol red. is incorporated for detecting carbohydrate fermentation that is indicated by the change in color of the carbohydrate medium from orange red to yellow in the pres...
Post a Comment
Read more

Simmons Citrate Agar biochemistry test for Enterobacteriaceae

By
Simmons Citrate Agar Simmons Citrate Agar  is an agar medium used for the differentiation of Enterobacteriaceae based on the utilization of citrate as the sole source of carbon.  Ingredients per liter of deionized water: Principle of Simmons Citrate Agar Uses of Simmons Citrate Agar 1.     It is used for the differentiation of Gram-negative bacteria on the basis of citrate utilization. 2.     Simmons Citrate Agar may be used to differentiate citrate-positive  Salmonella enteritidis  and members of  Salmonella  subgenus II, III and IV from the citrate-negative  Salmonella typhi, Salmonella paratyphi  A,  Salmonella pullorum  and  Salmonella gallinarum . 3.     Simmons Citrate Agar is primarily used to aid in the identification of Enterobacteriaceae. Uses include: Escherichia coli ...
Post a Comment
Read more

Simmons Citrate Test

By
Simmons Citrate Reaction It  used to differentiate among the Gram-Negative bacilli in the family Enterobacteriaceae. Principle  Citrate agar is used to test an organism’s ability to utilize citrate as a source of energy. The medium contains  citrate  as the sole  carbon source  and  inorganic ammonium salts (NH4H2PO4)  as the sole source of  nitrogen . Bacteria that can grow on this medium produce an enzyme,  citrate-permease , capable of converting  citrate  to  pyruvate .  Pyruvate  can then enter the organism’s metabolic cycle for the production of  energy . Growth is indicative of utilization of citrate, an intermediate metabolite in the  Krebs cycle . When the bacteria metabolize  citrate , the  ammonium salts  are broken down to  ammonia , which increases  alkalinity . The shift in pH turns the...
Post a Comment
Read more