MacConkey Agar is employed for the cultivation of enteric bacteria and in differentiation of lactose fermenters and nonfermenters. The medium contains bile salts to inhibit non-intestinal bacteria and lactose with neutral red indicator to distinguish the lactose-fermenting coliforms from the lactose-non-fermenting Salmonella and dysentery groups (1). MUG MacConkey Agar is based on the modification of MacConkey medium as per Trepeta and Edberg (2). It is used for the selective isolation and detection of lactose fermenting coliform organisms by a fluorogenic procedure. MUG MacConkey Agar helps to detect the presence of an enzyme ß-glucuronidase and thereby rapidly identifying Escherichia coli in mixed clinical specimens (3).
Peptic digest of animal tissue provides essential nitrogen compounds for the growth of coliforms. Lactose is the fermentable carbohydrates source. Bile salts and crystal violet inhibit the growth of gram-positive bacteria.
Neutral red is the pH indicator. MUG is cleaved by the enzyme ß-glucuronidase to release an end product 4-methylumbelliferone which produces a visible greenish-blue fluorescence under long wave ultra-violet light (366nm). The plates are exposed to ammonia fumes to increase fluorescence as suggested by Freir and Hartman (5).
The medium can be directly inoculated with the test specimen by streaking.
Storage and Shelf-life:
Store below 30°C in tightly closed container and prepared medium below 2-8°C. Use before expiry period on the label.
Reference:
1. Cruickshank R., Duguid J. P., Marmion B. P., Swain R. H. A., 1975, Medical Microbiology, Churchill Livingstone
2. Trepeta R. W. and Edberg S. C., 1984, J. Clin. Microbiol., 19 (2) :172.
3. MacFaddin J. F., 1985, Media for Isolation-Cultivation-Identification Maintenance of Medical Bacteria, Vol. I, Williams and Wilkins, Baltimore.
4. Maddocks J. L. and Greenan M. J. (1975) J. Clin. Pathol. 28. 686-687.
5. Freir T. A. and Hartman P. A. (1987) Appl. Env. Microbiol. 53. 1246-1250.