MACCONKEY AGAR (WITHOUT SALT)
Code: CM0507
A differential medium on which swarming of Proteus species is suppressed. Recommended for urine examination.
Typical Formula* | gm/litre |
Peptone | 20.0 |
Lactose | 10.0 |
Bile salts | 5.0 |
Neutral red | 0.075 |
Agar | 12.0 |
pH 7.4 ± 0.2 @ 25°C | |
* Adjusted as required to meet performance standards
Directions
Suspend 47g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes. Mix well before pouring. Dry the surface of the gel before inoculation.
Description
This medium has the same formulation as MacConkey Agar (CM0007) except that it does not contain added salt and therefore provides a `low electrolyte medium’ on which most Proteus species do not spread. For this reason the medium has found particular favour for use in the examination of urine so that overgrowth of other organisms is prevented.
Colonial Characteristics
After 24 hours at 35-37°C typical colonies are as follows:
Organism | Colour | Remarks |
Escherichia coli | red | non-mucoid |
Aerobacter aerogenes | pink | mucoid |
Enterococcus species | red | minute, round |
Staphylococcus species | pale pink | opaque |
Pseudomonas aeruginosa | green/brown | fluorescent growth |
Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared plates of medium at 2-8°C.
Appearance
Dehydrated medium: Straw pink coloured powder
Prepared medium: Dark red coloured gel
Quality control
Positive controls: | Expected results |
| Enterococcus faecalis ATCC® 29212 * | Good growth; red-coloured colonies |
| Staphylococcus aureus ATCC® 25923 * | Good growth; pale-pink coloured colonies |
Negative control: | |
Uninoculated medium | No change |