Recommended for selective isolation and differentiation of E.coli and other enteric bacteria from pharmaceutical products in accordance with the microbial limit testing by harmonized methodology of USP/EP/BP/JP.
Ingredients Gms / Litre
Gelatin peptone # 17.000
HMC peptone ## 3.000
Lactose monohydrate 10.000
Sodium chloride 5.000
Bile salts 1.500
Neutral red 0.030
Crystal violet 0.001
pH after sterilization ( at 25°C) 7.1±0.2
**Formula adjusted, standardized to suit performance parameters
# Pancreatic digest of gelatin
## Peptones (meat and casein)
Suspend 49.53 grams (the equivalent weight of dehydrated medium per litre) in 1000 ml purified/distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes or as per validated cycle. Cool to 45-50°C. Mix well before pouring into sterile Petri plates. The surface of the medium should be dry when inoculated.
Principle And Interpretation
MacConkey Agar is the earliest selective and differential medium for cultivation of coliform organisms (8,9). Subsequently MacConkey Agar and Broth have been recommended for use in microbiological examination of foodstuffs (10) and for direct plating / inoculation of water samples for coliform counts (1). This medium is also accepted by the Standard Methods for the Examination of Milk and Dairy Products (12). It is recommended in pharmaceutical preparations and is in accordance with the harmonized method of USP/EP/BP/JP (11,2,3,6).
Gelatin peptone and HMC peptone 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.
After enrichment of Escherichia coli in MacConkey Broth (MH083), it is then subcultured on MacConkey Agar. Gramnegative bacteria usually grow well on the medium and are differentiated by their ability to ferment lactose. 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.
Type of specimen
Pharmaceutical samples, Food and dairy samples, Water samples.