MacConkey Broth w/ Neutral Red
MacConkey Broth w/ Neutral Red M007S
MacConkey Broth w/ Neutral Red is used for selective enrichment and enumeration of coliforms.
Composition**
Ingredients Gms / Litre
Peptic digest of animal tissue 20.000
Lactose 10.000
Bile salts 5.000
Sodium chloride 5.000
Neutral red 0.070
Final pH ( at 25°C) 7.5±0.2
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 40.07 grams in 1000 ml distilled water. Heat if necessary to dissolve the medium completely. Distribute into test
tubes with inverted Durham tubes and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool the tubes before
inoculation.
Principle And Interpretation
MacConkey Broth is the earliest selective and differential medium for cultivation of enteric microorganisms from a variety of
clinical specimens (4,5). Subsequently MacConkey Broth have been recommended for use in microbiological examination of
foodstuffs (6) and for direct inoculation of water samples for coliform counts (7). This medium is also accepted by the Standard
Methods for the Examination of Milk and Dairy Products (8) and pharmaceutical preparations (9).
MacConkey Broth w/ Neutral Red is recommended by BIS under the specification IS:5887 (Part I) 1976 for Detection of
Bacteria responsible for food poisoning Part I : for Isolation, Identification and Enumeration of Escherichia coli . This culture
media is considered as a standard medium for the primary isolation as well as presumptive identification of coliaerogenes group
in food and water which contains neutral red as an indicator (1-3).
Bile salt inhibits most species of gram positive bacteria. Gram-negative bacteria usually grow well on the medium and are
differentiated by their ability to ferment lactose. Lactose fermenting strains grow as red. 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 typically do not alter appearance
of the medium.
Quality Control
Appearance
Pale yellow to pink coloured homogeneous free flowing powder
Colour and Clarity of prepared medium
Red clear solution without any precipitate
Reaction
Reaction of 4.0% w/v aqueous solution at 25°C. pH : 7.5±0.2
pH
7.30-7.70
Cultural Response
Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.
Cultural Response
Organism Inoculum
(CFU)
Growth Acid Gas
Cultural Response
Enterobacter aerogenes
ATCC 13048
50-100 luxuriant positive
reaction
positive
reaction
Escherichia coli ATCC
25922
50-100 luxuriant positive
reaction
positive
reaction
Salmonella Choleraesuis
ATCC 12011
50-100 fair to good negative
reaction
negative
reaction
Staphylococcus aureus
ATCC 25923
=10³ inhibited - -
Storage and Shelf Life
Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.
