(AB) MacConkey Broth, 500 grams

MacConkey Broth is a formulation recommended by the World Health Organization and is a modification of a formula developed by MacConkey. The broth medium is used for the presumptive determination of the presence of coliforms in water, milk and other sanitary materials. Presence of lactose- fermenting bacteria is detected by the change of color of the medium (from purple to yellow) after inoculation and incubation. The original formula used litmus as an indicator of acid reaction. Later investigations utilized neutral red as an indicator but was found to be inhibitory towards Esherichia coli. Bromcresol purple is now used since it is less inhibitory and gives distinct acid reactions. MacConkey Broth was formulated to support the growth of enteric bacteria and detect the presence of lactose fermenting bacteria. Bile (Oxgall) is incorporated into to the medium to inhibit gram-positive bacteria. Lactose is the fermentable carbohydrate and the fermentation reaction which gives an acid reaction is detected by the change in color of bromcresol purple from purple to yellow. MacConkey Broth is used to detect the presence of gram-negative, lactose-fermenting enteric bacteria in samples of water, milk and other materials of sanitary importance. (Alpha Biosciences # M13-111-500gm)

Use: MacConkey Broth is used to detect the presence of gram-negative, lactose-fermenting enteric bacteria in samples of water, milk and other materials of sanitary importance.

Description: MacConkey Broth is a formulation recommended by the World Health Organization and is a modification of a formula developed by MacConkey. The broth medium is used for the presumptive determination of the presence of coliforms in water, milk and other sanitary materials. Presence of lactose- fermenting bacteria is detected by the change of color of the medium (from purple to yellow) after inoculation and incubation. The original formula used litmus as an indicator of acid reaction. Later investigations utilized neutral red as an indicator but was found to be inhibitory towards Esherichia coli. Bromcresol purple is now used since it is less inhibitory and gives distinct acid reactions. MacConkey Broth was formulated to support the growth of enteric bacteria and detect the presence of lactose fermenting bacteria. Bile (Oxgall) is incorporated into to the medium to inhibit gram-positive bacteria. Lactose is the fermentable carbohydrate and the fermentation reaction which gives an acid reaction is detected by the change in color of bromcresol purple from purple to yellow.

Formula* per Liter:

• Pancreatic Digest of Gelatin......... 20.0g
• Lactose ..........................................10.0g
• Oxgall ................................................5.0g
• Bromcresol Purple ......................... 1.5g

Final pH: 7.3 ± 0.2 at 25.0°C

* Grams per liter may be adj. or formula supplemented to obtain desired performance

Preparation: Mix 35 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. Dispense into test tubes containing Durham tubes. Autoclave at 121.0°C for 15 minutes.

Quality Control Specifications:

1. The powder is homogeneous, free flowing and light pinkish-beige.
2. Visually the prepared medium is clear to slightly hazy and medium to dark pinkish purple.
3. Expected cultural response after 18-24 hours at 35.0°C.

Organism                                                                                    Result

Enterobacter aerogenes ATCC 13048                           Growth, Yellow, Gas +

Escherichia coli ATCC 25922                                         Growth, Yellow, Gas +

Salmonella typhimurium ATCC 14028                            Growth, Purple ,Gas -

Enterococcus faecalis ATCC 29212                                   Growth Inhibited

Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light pinkish-beige color.